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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: OldsFan on May 05, 2014, 09:01:49 pm
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My carb's float went bad (filled with gas), so I pulled the carb apart and rebuilt it. I have a 17085226 Q-Jet (non-computer). It isn't my first time rebuilding a Q-Jet, so no big deal, I thought. :)
Put the freshly rebuilt carb back on the engine and it starts up, runs and idles fine. I adjusted the idle mix, etc. etc. I drove it around a little bit and everything seemed fine. I didn't run it hard and part-throttle acceleration was and is fine.
Today, I took it out to setup the secondary air doors and found a problem, though. If I just stab the throttle hard, it falls on its face for a second or two and then gets up and goes. I put a vac gauge on it and it hits and holds zero vac during that stumble. I figured it was that the spring for the air doors was just too loose.
But here's where it gets strange:
It has the same stumble in neutral. If I just punch it in neutral, it actually stumbles (but for a shorter time). I pulled the air cleaner and watched as I cranked open the throttle with my hand. I don't even see the secondary doors moving but it still stumbles!!! :-\
What could cause this? Could it be the accelerator pump shot being wrong or not enough? Any other ideas?
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There are a large number of potential causes for stumble on acceleration. Since the carb was just rebuilt, initial thoughts are low float level, inadequate accelerator pump shot, sticky power piston, warped fuel bowl cover. Engine bog can also be caused by inadequate ignition timing, or a sloppy timing chain.
Consider this question carefully: When you romp on the throttle, is the bog instantaneous with throttle motion... or does the engine begin to accelerate for 1/2 to 3/4 second and then bog?
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I had a similar problem a couple of months ago. I installed a cheap carb kit in a quadrajet and is ran good for a day and then developed the same stumble on acceleration. It turned out that the rubber seal on the accelerator pump swelled up and came off of the piston. Apparently this is becoming a common problem with todays fuels. I ended up doing a search and found www.cliffshighperformance.com/ He claims the materials in his kit are resistant to this issue. I installed the kit and it has ran smooth ever since. It is worth removing the top and taking a look.
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Just a quick tip! If you remove the roll pin from the accelerator pump arm, just enough to remove the arm, the top comes off a lot easier.
Seeing that you have done your fair share of Q-Jet builds I'm sure you know this, but I thought I'd mention it for readers not so familiar with them.
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I had a similar problem a couple of months ago. I installed a cheap carb kit in a quadrajet and is ran good for a day and then developed the same stumble on acceleration. It turned out that the rubber seal on the accelerator pump swelled up and came off of the piston. Apparently this is becoming a common problem with todays fuels. I ended up doing a search and found www.cliffshighperformance.com/ He claims the materials in his kit are resistant to this issue. I installed the kit and it has ran smooth ever since. It is worth removing the top and taking a look.
Google: GM 17110591 Viton Pump Kit
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Another couple of possible issues that masquerade as an accelerator pump issue.
- Talking to an old speed shop mechanic, he said that the connectors on the wires from the distributor shaft sensor to the ignition control module can get flaky. When you get on it, and the vacuum advance comes off, the sensor rotates around the shaft and you can lose contact to the ICM. The stumble is similar to an accelerator pump issue. Not likely in your case, because it would have to be a coincidence to happen at the same time you replaced the carb.
- The other ignition timing issue can be too little advance. At low rpm (centrifugal advance not in), you open the throttle (dumping the vacuum, so vacuum advance is not in), and the timing goes way retarded. Again, the stumble is similar to an accelerator pump issue. Again, probably not your issue, but it could be if the distributor isn't clamped down hard and you moved it replacing the carb. You probably should be running 14-18 degrees of base timing (with the vacuum disconnected) if it is an SBC.
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Wow! I thought for sure nobody would bother with my question about my Qjet. You guys have given me EXCELLENT responses and ideas!!
So to answer the questions:
bd - The stumble is IMMEDIATE. There's no beginning of an acceleration, but the engine does not completely stall either (comes close, though). I figured if the pump shot were not working it would just stall out altogether... On the float level, I got a brass float which has the rounded edges so setting the level perfectly was hard. I thought I got it close, but it is worth a second look. I'll also check the accelerator pump... See my note on the timing in response to bd below.
Big Katz - The kit I got was from NAPA and included the new "blue" style accelerator pump seal... BUT, it doesn't say anything about ethanol compatibility. Still, I've used probably 5 Napa kits on other carbs and not had an issue. I'll check this though! Are the NAPA kits generally ok?
BADAZ - Yes, good point. I like to put a flat screwdriver between the roll pin and the housing - leaves a little space making it easier to get it back into place later.
Rich - I have the 5 pin HEI module with the knock-sensor electronic setback. It did still work last time I checked it, but it shouldn't be hard to check again.
Now - the timing is another thing. I set it way back to about 9 degrees BTDC (sticker actually says 6 is stock, :-) ) from about 14 degrees. I did this right after installing the rebuilt carb just to add a measure of "safety" against knock in there until I have everything worked out. Do you think that could really be causing it??? :o
So one other thing came to mind. My carb is an M4MED model with the "D" standing for "Dual Capacity Pump". There's an electrical connection on the top of the carb which pushes down a pin inside. I think when the engine reaches operating temp that switch reduces the pump capacity. I am wondering if that has something to do with it. I am going to try and check that switch as well just with a 9 volt battery or something. For those reading this later - it is the grey connector, not the blue one on Computer Controlled Quadrajets.
There's a great post on M4MED's here: http://forum.73-87chevytrucks.com/smforum/index.php?topic=11916.0 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=11916.0)
Thanks again guys! I really appreciate the suggestions and more are welcome. I'll follow up once I have a few minutes to tear into it again.
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The blue pump diaphragms are Viton and should function fine with enriched fuels.
"Immediate" hesitation with base timing correctly adjusted is generally insufficient fuel delivery. But... you stated the problem began after retarding the timing 5° from where it had been (done at the same time as the carb OH). So....
Things to do:
Return the timing to its pre-hesitation setting to eliminate base timing as a variable - what happens?
Try hovering the carburetor with a gloved hand and a shop towel to enrichen fuel delivery as you rap the throttle - what happens?
The M4MED dual capacity pump functions just as you're thinking, except it energizes before reaching operating temp. Unplug it - what happens?
Finally, with your posting on timing I have to ask: Have you verified timing chain wear and the balancer timing marks?
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Ok, your suggestions led me right to it.
I checked the balancer just recently with a piston stop and there was "almost" no slop that I could detect in the timing chain. The motor only have about 67K miles on it...
Anyhow, looking down the primary barrels with flashlight (at night), I can see that there is very little pump shot. On older Q-Jets I get a solid stream coming out, with this one I am getting just some dribbling down the side of the barrels. :-\
Even after shutting the engine down and rapping the throttle open I just get a little drizzle - that can't be right. The dual pump energized or not doesn't make a difference. It's both sides.
I'll pull the top off the carb this weekend and see what is going on with it. Maybe the umbrella-type pump seal got unseated or something... I'll let you know what I find.
I really appreciate the help on this, though. If nothing else, I finally learned how the dual capacity pump deal functions. :)
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Ok, sorry it took so long but I finally had time to track a few things down.
I am pretty sure I am having an issue with the dual-capacity solenoid. I pulled the carb apart and replaced the accelerator pump. It runs much better, but when cold there is still a stumble. Once it warms up the stumble is gone.
I tested the solenoid itself and it is working (pushes the little plunger down when it gets 12 volts). Also, I checked the electrical switches and it appears it gets power when cold and not once it warms up.
So here's the question... How does that dual capacity system work? Can I take the bottom of it out somehow? I read through my info on the carb, including Ruggle's book, but there's not much coverage on the actual function of that system inside the bowl. Could it be plugged or otherwise defective?
Any help on this appreciated!
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See page 6C1-29 (pg 749) of the 1986 Service Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/X8632_1986_GMC_Light_Duty_Truck_CK_G_P_10_to_30_Service_Manual.pdf) for the M4MED dual capacity pump diagnostic steps. The procedure is pretty straightforward. Energizing the solenoid should decrease the pump shot...
I checked the electrical switches and it appears it gets power when cold and not once it warms up.
You need to figure out why it's energizing when cold instead of when warm. Faulty or incorrect thermal switch, perhaps. Did someone cobble the wiring or modify the circuit?
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Ok, first thank you for that link!!! That does that make it a heck of a lot easier to troubleshoot.
Second, I got that mixed up. The solenoid gets power all the time (key on), but it never grounds. That is, I hooked up a multimeter and checked and even when fully warmed up (180* thermostat open), it only shows about 5 volts between the solenoid connection and the thermal switch contact. I think the thermal switch is bad. When I short it to ground, I can hear the solenoid clicking, so I am going to work on finding a new thermal switch. Fixing that may help some things...
Another question, though - I noticed that if I press it and hold it down for a few seconds, it takes 3-5 seconds or so to come back up. I don't seem to remember that on any other carb I've got. How long should it take the accelerator pump to come back up from being fully depressed and held until it empties??? Should it spring right back or take some time to refill?
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Expand on this...
...even when fully warmed up (180* thermostat open), it only shows about 5 volts between the solenoid connection and the thermal switch contact....
Where are you connecting the voltmeter leads to measure 5 volts? I don't have a reference on the temperature calibration of the sensor. The 180° thermostat maybe too cold.
But, I want you to think about something for a moment. Energizing the solenoid decreases the pump shot. You're experiencing a lean throttle opening, now. What do you suppose will happen when you get the dual-capacity solenoid working?
...Another question, though - I noticed that if I press it and hold it down for a few seconds, it takes 3-5 seconds or so to come back up. ...How long should it take the accelerator pump to come back up from being fully depressed and held until it empties??? Should it spring right back or take some time to refill?
There's a spring under the accelerator pump that should return the pump immediately. You have a pump cup that is sticking in the bore - not good. What pump did you use last (brand & P/N)? Did you replace the pump shaft seal that is staked into the bowl cover (if the M4MED uses one)?
You may need to polish (hone) the accelerator pump bore and use a different cup material. More on that after you respond to this round of banter.
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Hey Rich... Thanks for the responses. So here goes:
Where are you connecting the voltmeter leads to measure 5 volts?
I hooked up one lead (+) to the battery positive. I hooked up the other to the pin coming out of the temp switch on the water neck. I got 5 Volts and a high Ohm reading (don't remember what). I also tried hooking the positive to the lead that goes to the solenoid and kept the negative lead in place (engine on, full temp) and got a slightly lower rating but near 5 Volts. Also, it seems to be 5 volts regardless of temp.
What do you suppose will happen when you get the dual-capacity solenoid working?
Yeah, I know... I was just hoping for some sort of miracle. ;D Either way, I intend to get this working, so I want to make sure I find the right switch to replace it.
You have a pump cup that is sticking in the bore - not good.
Just what I was thinking. The odd thing here is that it moves down smoothly and it comes back up smoothly, just slowly. If I pull upwards on it, it almost feels like I am working against a vacuum - hard to explain, but it pulls back down sorta'... I've never tried to just yank it, so I am talking about gently pulling on it with fingers, no tools.
Did you replace the pump shaft seal that is staked into the bowl cover (if the M4MED uses one)?
It does and yes, I replaced it. :)
What pump did you use last (brand & P/N)?
Napa ECHLIN, part 2-4055 (V12268, Made in USA). I reused the return and duration springs on the new pump because it did not come with one.
You may need to polish (hone) the accelerator pump bore and use a different cup material. More on that after you respond to this round of banter.
How would I polish it? I mean, I need something that will clean up the bore without increasing it or mis-shaping it... Maybe a really fine grit sandpaper? Polishing compound...? Thanks for all the help - I am pretty determined to get this working. ;D
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Where are you connecting the voltmeter leads to measure 5 volts?
I hooked up one lead (+) to the battery positive. I hooked up the other to the pin coming out of the temp switch on the water neck. I got 5 Volts and a high Ohm reading (don't remember what). I also tried hooking the positive to the lead that goes to the solenoid and kept the negative lead in place (engine on, full temp) and got a slightly lower rating but near 5 Volts. Also, it seems to be 5 volts regardless of temp.
With the dual-capacity solenoid connected to, or disconnected from the switch? Ignition on or off? The way you describe it I'm not convinced that the measurement is valid or meaningful.
You have a pump cup that is sticking in the bore - not good.
Just what I was thinking. The odd thing here is that it moves down smoothly and it comes back up smoothly, just slowly. If I pull upwards on it, it almost feels like I am working against a vacuum - hard to explain, but it pulls back down sorta'... I've never tried to just yank it, so I am talking about gently pulling on it with fingers, no tools.
What pump did you use last (brand & P/N)?
Napa ECHLIN, part 2-4055 (V12268, Made in USA). I reused the return and duration springs on the new pump because it did not come with one.
Pick up a GM 1711591 pump kit.
Did you replace the pump shaft seal that is staked into the bowl cover (if the M4MED uses one)?
It does and yes, I replaced it. :)
Lubricate the accelerator pump shaft and seal with a miniscule smear of silicon dielectric grease. But, use it very sparingly so none of the silicon compound drips into the fuel bowl. Even small amounts of silicon will damage O2 sensors, making them ineffective.
You may need to polish (hone) the accelerator pump bore and use a different cup material. More on that after you respond to this round of banter.
How would I polish it? I mean, I need something that will clean up the bore without increasing it or mis-shaping it... Maybe a really fine grit sandpaper? Polishing compound...? Thanks for all the help - I am pretty determined to get this working. ;D
Procure a ~3" long 1/4" bolt. Cut the head off the bolt. Use a hack saw to split the threaded end of the bolt lengthwise ~1.25" (or ~0.25" less than the width of a roll of 120-grit emery). Now you have an arbor. Clamp the arbor in a 1/4" die grinder. Wrap about a 3 - 4" length of emery around the slotted end of the arbor.
Remove the valve and check in the base of the accelerator pump bore. Then, use the makeshift hone just as you would use any hone, moving in and out of the pump bore to create a crosshatch pattern. 120 emery will remove material very gradually and nicely polish the bore.
Clean the bowl and bore with some carburetor cleaner and compressed air. Sparingly lube the pump cup with a light smear of ATF and reassemble. The pump should slide in the bore very smoothly with little resistance.
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Ok, so I pulled the carb and figured a few things out.
1) You're 100% right. The accelerator pump cup seal is getting hung up and causing issues. Take a look at the pics to see what I mean. That's how it came out of the bore, with the cup seal wrapped around the return spring.
2) I compared the original pump and the new one and it looks like they are the same. Measured with a caliper, the inner plastic pieces are a couple thousandths off. The outer seal on the original is obviously much smaller, but also pretty worn out.
I am going to come back on the dual-capacity solenoid stuff. You may be right, but I am thinking of replacing the temp switch just in case. Still, lemme get the carb right first, then we'll troubleshoot that... :)
Pick up a GM 1711591 pump kit.
Is there a good place to get these? Do you think the Napa ones are no good?
Even small amounts of silicon will damage O2 sensors, making them ineffective.
No O2 sensors on my truck. No CCC, just a knock sensor and electronic spark retarder. Still, I get the picture and good you mentioned it. :) Was thinking of putting in a wideband, so it is a good idea either way.
As far as the procedure for polishing up the bore, that sounds great. I think I understand exactly what you are describing. Just one question... You mentioned that I should "Remove the valve and check in the base of the accelerator pump bore." What did you mean by "check in the base" of the bore? Were you talking about removing the check ball that is under the screw next to the pump bore?
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Enriched fuels take their toll on rubber compounds. Some pump cup materials are more prone to swelling than others. From the image you posted, it seems that applies to the Napa pumps.
Typo on the GM part number - it should have read 17110591.
The 17110591 cup is made from Viton and has a distinctive red color. I installed literally hundreds of these before the advent of factory injection to resolve pump cup distortion issues resulting from enriched fuels; and I enjoyed great success. Likewise on burnishing the pump wells. The pump kit "should" be available through any Chevy/GMC dealer or AC Delco retailer. You can Google the P/N as well, with hits on Ebay, etc. Tip: Spray the plastic cone in the kit with WD-40 to make installation onto the plunger assembly easier. Then, install the cup and expander spring together in one step.
I mentioned silicon contamination of O2 sensors, because of your earlier thread on the wideband installation. ;)
Remove the dual-capacity valve below the solenoid and remove the accelerator pump check ball under the screw retainer, because polishing the bore will produce fine abrasive particles that will find their way into the pump passages. That way you can wash and blow the passages clean when your done, prior to reassembly.
If you measure the voltage drop across the DC Temp Switch with the circuit connected and ignition switched on, you should measure the same voltage as that supplied to the solenoid, until the engine heats to temperature and the switch closes. At the point the switch closes, you should measure zero volt drop across the switch. The switch is digital. It's either open or closed. Resistance through the switch should be infinite when cold, switching suddenly to zero as it closes when the engine heats sufficiently.
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Ahhh... The improved part number helps a lot. I was wondering why I couldn't find it googling it before. I'll order one tonight.
I mentioned silicon contamination of O2 sensors, because of your earlier thread on the wideband installation. ;)
Wow. Your memory is better than mine! I barely remember talking about that and once the carb started acting up, just put it out of my mind altogether.
Remove the dual-capacity valve below the solenoid.
Yeah, this is the one thing I haven't figured out how to do. Looks like you could use a pair of screwdrivers to twist it out or maybe needle-nose pliers? I think it is just threaded in there, right?
Oh yeah, are you sure on the 120 grit emery? I picked up some, but it feels pretty rough, like it might tear up the bore. I got some 1200 as well, just in case.
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Remove the dual-capacity valve below the solenoid.
Yeah, this is the one thing I haven't figured out how to do. Looks like you could use a pair of screwdrivers to twist it out or maybe needle-nose pliers? I think it is just threaded in there, right?
There is actually a "special tool" for that - lol (It seems there are special tools for e/g - need to keep the tool companies happy I guess ::)). Get a large screwdriver that will fit the slot then notch it with a file or hack saw for plunger clearance. It just threads in. There are some select dash nut sockets that work, too.
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Oh yeah, are you sure on the 120 grit emery? I picked up some, but it feels pretty rough, like it might tear up the bore. I got some 1200 as well, just in case.
At 20,000 RPM, 120 should work just fine. Remember, it's only a 1/4" arbor. The paper will unwrap and expand outward to polish the bore. You will not be applying pressure to the bore with the arbor. Perhaps, "polish" is the wrong word. You're not trying to create a shiny bore - rather you are breaking any wear marks and smoothing the bore with a very fine crosshatch pattern. The entire process generally takes only about 5 - 10 seconds with the hone to achieve a finished surface. If you are uncomfortable using 120, go finer. But, you're not wet sanding paint - 1200 will take a l-o-n-g time.
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Ok, I understand. I pulled the carb apart tonight and tried to "feel" it with my finger. It isn't rough like sandpaper or anything, but clearly it isn't right. The pump hangs up badly when it is dry. The old one just drops right in there. But I think it is original to the carb, so it may have just shrunken and dried out over the years.
I'm going to let things dry out a bit before I try to burnish the bore. Even a small amount of gas and sparks sounds like a bad idea. :o
I ordered the GM pump you recommended. That'll take a couple days to get here.
In the meantime, two more questions related to this:
-Did they make multiple size accelerator pumps? The original just looks so much smaller than its replacement.
-I noticed that driving around with the carb after the rebuild, it took more cranking to get it to start after sitting than it used to. It isn't a lot more cranking. Let me put it this way - before, if I let the truck sit for 6 hours, it would start instantly with two pumps of the pedal. After the rebuild it was taking more like 5 seconds. Could this be because the accelerator pump was messed up and the pumps of the pedal had basically no effect?
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Ok, I understand. I pulled the carb apart tonight and tried to "feel" it with my finger. It isn't rough like sandpaper or anything, but clearly it isn't right. The pump hangs up badly when it is dry. The old one just drops right in there. But I think it is original to the carb, so it may have just shrunken and dried out over the years.
I'm going to let things dry out a bit before I try to burnish the bore. Even a small amount of gas and sparks sounds like a bad idea. :o
I ordered the GM pump you recommended. That'll take a couple days to get here.
In the meantime, two more questions related to this:
-Did they make multiple size accelerator pumps? The original just looks so much smaller than its replacement.
-I noticed that driving around with the carb after the rebuild, it took more cranking to get it to start after sitting than it used to. It isn't a lot more cranking. Let me put it this way - before, if I let the truck sit for 6 hours, it would start instantly with two pumps of the pedal. After the rebuild it was taking more like 5 seconds. Could this be because the accelerator pump was messed up and the pumps of the pedal had basically no effect?
Bore diameters have been fairly consistent for a long time. However, pumps were manufactured in various lengths. Compare the original pump to the service replacement. Are they the same length? With the duration spring removed, wiggle the upper shaft where it enters the lower plastic cup holder on both pumps and compare the amount of looseness. Are they similar or notably different? If the pumps are different lengths, use the original. If the pumps are the same length, but the newer pump has less 'wiggle,' use the newer pump. The 17110591 pump and expander spring will be slipped onto one of the two plungers.
As to differences in starting, before and after your rebuild... you installed a new float and set the float level (the old one was heavy), you replaced the accelerator pump (the old one was worn undersized, the new one stuck in its bore), you adjusted the idle mixture screws, perhaps you epoxied the various fuel well plugs (you didn't say), nearly all Qjets exhibit warped fuel bowl covers, etc, etc, etc. Is there any wonder that fuel delivery changed?
Remember when you "fit" the new pump (lubricated with ATF or a sparse amount of silicon grease) into the bore, it should slide like silk while providing a positive seal and strong pump shot. And, don't forget to reinstall the ball check, etc, after thoroughly cleaning the passageways.
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Hey Rich - I finally had some time this weekend to do this. It seems to have worked. I was concerned about the 120, so I used 220 grit and just worked it a little longer. It caused a lot of white dust to be spit back out and seems to have cleaned up the bore a lot. I cleaned it thoroughly with Berrymans and let it dry out over night. After that, I just dropped the check ball back into place and screwed it and everything else back down.
Initially, the pump was still coming back up somewhat slowly, but then I put some silicone dielectric grease on it just above the air horn. That made all the difference! I tried it out and there is now no stumble when cold or hot. It actually seems to be a lot smoother than before. The thing that has me concerned is just that the stupid seal is obviously gripping the pump shaft a bit too tightly. I guess I'll have to re-apply the grease now and again. :-\
So, coming back to your other comments...
-Yeah, I ended up keeping the original pump but putting the new seal and garter spring on it. The pumps were very, very similar, but I figured the original had worked for years and seemed "tight" enough after the test you mentioned.
-Starting is also greatly improved. Two pumps and she fires up on the first crank. I am thinking that the pump seal was so bad that it wasn't putting any fuel into the bore and so it was taking a long time to raise the mixture to an appropriate level without it.
-I tried something new on the well plugs this time. I found some epoxy that was listed for being "gasoline resistant" and able to be used to fix fuel tanks. I forget now what it was called, but I'll look it up. I've always used JB-Weld in the past and had good luck with it, but I figured on trying something else out. As long as it stays put, I should be ok... :)
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Congrats!
Regarding the pump shaft seal in the bowl cover, I suspect that it was staked too tightly, causing it to compress slightly - hence expand inward, tightening around the shaft(?).
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Ok, so assuming you are right about the shaft seal... And it is altogether possible -
Do you think I should pull the air horn and replace the seal and try to just drop it back into place? I had a lot of trouble replacing that seal and getting the washer-like backer to stake back into place, so I may have overdone it.
Also, can you tell me how you would test that temp switch for the dual capacity pump shot? I mean, the truck is driveable (and runs quite happily again), but I don't think the temp switch is ever grounding. Because of that, the pump shot does not get reduced when the engine reaches operating temperature.
If you think it doesn't really matter, I'll let it go - but my overall goal is to make it perform as well as it can. To be fair, I am pretty sure this wasn't functioning before my rebuild either. Take a look at the attached pic. The crud in there is (obviously) from when I was tearing it down. Don't worry, that's long gone now! :)
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The accelerator pump shaft seal may relax with use and not require further attention, so I wouldn't pursue the seal unless it continues to bind the pump. For future reference, the pump shaft seal rarely needs to be replaced during an overhaul. Carburetor cleaner doesn't affect the seal and they almost never wear out.
You can check the dual capacity temperature switch with a voltmeter or an ohmmeter. The temp switch is OFF-ON and either open (cold) or closed (warm).
Voltmeter: Measuring the voltage drop across a cold dual capacity temperature switch with the circuit connected and ignition switched ON should register the same voltage as that supplied to the dual capacity solenoid. Once the engine heats to operating temperature and the switch closes, you should measure "zero" volt drop across the switch.
Ohmmeter: Resistance measured through the switch with the switch unplugged from its circuit should be infinite when cold, switching abruptly to "zero" ohms as it closes from engine heat.
As to whether you should "restore function" to the dual capacity pump (DCP), you stated that the engine presently accelerates well with no hesitation when cold or hot. Well, the DCP is designed to decrease the pump shot when warm, which could introduce a warm hesitation. Why not try this simple test. Bring the engine to operating temperature, ground the temp switch wire to energize the solenoid, and then test drive it. Determine what effect the DCP will have on drivability. Then decide for yourself and post the results.