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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: 87_Rado on May 20, 2020, 01:42:55 PM
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How is everyone doing. Been a while since I've posted anything but I'm running into an issue with my 87 with the 350 TBI set up. I'm having trouble with it lacking power in take off and will want to stall on idle and when put into gear. I put a new pump and sending unit in the tank when I first started the project. From my understanding is that the fuel feed should be 3/8, the return should be 5/16 and then then vent. I recently rebuilt the throttle body with all new gaskets and seals and cleaned everything very well. Still no help on the sluggish power and stallling issue. The truck is throwing a code 44 which is a lean code. 02 sensor was replaced maybe a year ago. I checked all around the base gaskets and vacuum lines with carb clean to look for a possible vacuum leak. Still no help. Egr and solenoid replaced not to long ago with all new lines as well. New PCV valve. I've done slot of work to it to try to figure this out. I'm remembering that I sprung a leak in the hard fuel lines coming from the tank that run along the bottom of the cab, in-between the cab and the bed. I replaced it with soft runner line that run to the frame rails but I used all 5/16 lines for Feed, return and vent... Do you guys think this could be my issue!? Will 3/8 on the feed/pressure side make that big of a difference over 5/16? Let me know what you guys think please any little bit of advice or other suggestions would help! Much appreciated in advance 👍🤘
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I think it could make a difference and a kick or blockage can further complicate things. Make sure your tanks are clean of rust and debris (ethanol can mess up the fuel system - it did mine anyhow) , filters clear, and I would install a 3/8 line, some say 1/2 lines.
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Sounds like blockage of some sort.
Remove your doubt by installing correct size lines.
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Thank you guys for the response 👍 I'm going to add the 3/8 FI rated fuel line today and make sure the line is free of any kinks. I just added a new inline filter so I know that is not the cause. I'm really hoping this line does me justice because I've been chasing this issue for quite some time. I'm also going to throw a new NTK 02 sensor In if napa has one. Just to remove the doubt like Johnny popper said. I will check back after the job is done. Any other suggestions is still much appreciated thanks again guys 🤘
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Well I guess it's back to the drawing board fellas. Yet another attempt with no success.. I spent the better have of my day dropping the fuel tank and plumbing in the correct size lines. Pulled the pump, Cleaned the screen, which looked good anyways. Ran fresh fuel lines, 3/8 for feed, 5/16 for return and 1/4 for vent. No blockage or kings anywhere in the line, and put another brand new filter In line. I'm stumped again I took it for a ride and it's made absolutely no difference at all. Any other suggestions fellas? Cap and rotor is new, plugs and wires are new, coil is new. Ignition control module was just replaced. All parts less than two weeks old due to no spark. But the truck is just running like crap and I would love to get this figured out. Any other advice is much appreciated.
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What is the measured fuel pressure? Do you have a scan tool?
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BD, thanks for the responses. I do not have a scan tool. I would like to get one and I spoke with another member about it but I'm not sure of a decent model for a decent price.. I just ordered the guage and adapter from cfm technologies. Going to install that when it comes in to verify fuel pressure. It seems like it runs leans and then adjust the fuel trim to compensate and feels like it's dumping fuel. I'll have to feather the gas at idle and coming to a stop to try and keep it running.
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Other than increasing susceptibility to engine ping, does unplugging the vacuum line from the EGR valve improve the symptoms?
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I have tried unplugging those and it didn't make a difference. I went ahead and replaced the egr and the solenoid and the vacuum lines anyways, just to remove the doubt. Im actually taking a drive right now and I read somewhere on the forum to try and unplug the CTS and MAP sensors and see if that makes a difference and it's seems have to significantly improved my drivability. Haven't had to feather it coming to stops and idle seems to have smoothed out after driving and coming to a stop. Still a little rough on start up but overall it's much better than it was with the sensors plugged in. Any ideas why this may be / what would cause this? I appreciate the quick responses 👍
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Lot's of parts changing and guess work here. You could have low fuel pressure, faulty TPS, yadda yadda. You should get a scan tool and fuel pressure gauge. It would save you time and money!
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Fuel pressure gauge is on order and will be installed as soon as possible. The scan tool I am looking for a recommendation you can still purchase that is decently priced, so if you have an option there let me know. I'm just a diy guy. I've been trying to solve it myself but countless fails has led me to ask for advice on the forum. As I said before the recommendations or suggestions is always helpful and appreciatied thanks again 👍
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87_Rado, when the sensors are disconnected the ECM defaults to a fixed program with limited dynamic input.
I totally agree with Vile. You need a scanner, a DVM, and a fuel pressure gauge to diagnose elusive TBI issues. Typically, the more you spend on a scanner the greater its functionality. If you need to purchase in a hurry your options may be more limited than when there is ample time to be selective with no pressure. As Vile posted elsewhere, there are many options with a broad range of prices and functionality.
I use a Bosch OBD 1300 available from O'Reillys Auto Parts because of its ready availability and OBD 1 and OBD 2 functionality. Other options are available (Innova, Actron, et al). Bear in mind that no single scanner is perfect. And, they become quite pricey as capabilities increase.
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Okay sounds good I will look into the Bosch because I would love to get this figured out once and for all. As of right now I'll be leaving the sensors unplugged because it runs 10x better that way. Fuel pressure gauge is on the way so I will keep you posted on that. What is a dvm?
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Digital Volt Meter
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Ohh okay lol yeah I'm good with a volt meter. I'm fully capable of doing any trouble shooting/testing I just don't have the knowledge of these trucks, as to what to test and why that's all.
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Well if you have a good meter, you can backprobe some sensors and perform tests on them but that scan data is what's going to help you the most.
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I have a good meter but that's exactly what I'm saying. I'm fully able to test them, I just don't know how to perform the test for each specific sensor as far as what values I should be looking for. Volts, resistance etc..
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Dynamic measurements are the best. So backprobing and measuring the voltage is much better than resistance testing the component. Example, how to test the TPS, bottom post http://forum.73-87chevytrucks.com/smforum/index.php?topic=20131.0
You can do the same tests for the MAP sensor using a handheld vacuum pump and so on but again! Get a method of reading scan data. Where do you live? Did you check craigslist and Facebook Marketplace? I'm sure you can find a used OBD1 scanner cheap.
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I'm in Neversink, NY. It's in the hudson valley/Catskills area. And ill check Craigslist now and letgo. I don't have Facebook so I can't do the market place unfortunately. But thank you alot for the response vile. I have learned alot from you, Capt, BD and many other just from hours of reading other post other than mine. I'm definitely gonna get a scanner as soon as I can ive been in need of one for a long time
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Also when I was doing the fuel lines on my truck I removed the fuel switching valve or whatever for the duel tank set up. Because I only have one tank currently. The mounting bracket is broken but if anyone would like this valve they can have it. I'm not sure where to post it but I'm sure there someone out there looking for one
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Alright fellas back again. My fuel pressure gauge and adapter arrived yesterday evening so I'm going to install it this afternoon. What's the ideal fuel pressure that I should be looking for?
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Got the adapter and guage installed. After a little tweaking I'm now leak free and it's showing a constant 8-ish PSI.. What do we think? I thought I was supposed to be closer to 11 if I'm not mistaken, but I'm no expert here.
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Fuel pressure should be ~11 PSI. Temporarily pinch off the fuel return hose and remeasure the fuel pressure. What is it?
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BD, I pinched the return line off and didn't make much of a difference. Maybe a hair closer to 9 but nothing significantly changed. I'm definitely no where near 11. I'm at a steady 8 - 8.5 psi.
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Remove the fuel filter and blow through it. Is there any restriction?
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No restrictions. Brand new lines all the way up..(The correct size this time) and brand new filter. I just spend most of the day last week and I dropped the fuel tank. Re-plumbed all my lines from the tank up and while I had the tank out I removed the pump and sending unit for inspection. The screen seemed fine and I cleaned it anyways since it was out.
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Measure the pump voltage and verify a good ground. If power and ground to the pump are adequate, you have e/g correctly plumbed with no leaks (including inside the tank), and there are no restrictions, replace the pump.
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Inside the tank is all hard lines, they were in good shape from what I can see. Replaced the sending unit about 5 years ago when I bought the truck. And I know I have good ground I just cleaned up the surface before re-attaching when I had the tank out. What voltage am I looking for to the pump? And if a new pump is on the list do you have a recommendation? Thank you for the responses I'd love to get this thing running how it should and get this figured out.
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It's a 12v truck, right? ::)
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9-13 PSI is spec
http://forum.73-87chevytrucks.com/smforum/index.php?topic=37750.0
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Thank you for the response and yes I have 12v at the pump connector behind the cab. I'm thinking It could possibly be the pump because I have done all off the trouble shooting that was explained In that post vile.
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AC Delco EP386
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Thank you, much appreciated. That's just a factory replacement for the tbi pump? I hope this will make a big difference for me. Gonna order it from my local AutoZone or napa tomorrow. It' amazes me how the truck still runs and drives fairly decent at times minus the occasional hard start and stalling from time to time. It's had this problem ever since I bought it. And I replaced the fuel pump right before I put it on the road. I'm wondering if I put the wrong pump in 5 years ago.. Maybe put a carb one in there or something without knowing it. I've just been dealing with the issues but I'm tired of it and want it done right so I guess Ill take a chance at a new pump and have to drop the tank again.
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I believe the EP386 is a factory superseded part number - nothing fancy. You may need to upgrade the original connector, but it is supplied with the pump along with new tank unit o-rings. After you remove the fuel pickup, before disturbing the pump mounting, check the condition of the rubber coupler hose that connects the pump to the steel standpipe. See if it's spongy, split, distorted, or dislodged.
FYI - the EP386 pump does not ship with a new filter sock. I suggest replacing that too: AC Delco TS6. Be sure to recheck the fuel pressure after pump replacement.
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BD thanks again your kindness and patience is much appreciated. I will replace the pump and the sock at the same time and check back. It'll probably be a week or two before I get parts and motivated to drop the tank again. I will definitely keep you posted and hopefully we will have solved the issue. Your quick responses have been very helpful 🤘👍
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Many of the older pumps came with a pulsator which would rupture inside the tank. Make sure you eliminate it if you have one. Just use the hose connection and clamps directly to the feed pipe.
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Ordered the pump and filter sock, it will be in tomorrow morning. Fingers crossed that this will solve my issues. And Vile I will check that when I remove the pump. I'm pretty positive mine just has the rubber hose in-between the pump and hard line but I will check to be sure.
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Well fellas thank you all for the help, the support on this site is awesome. I installed the new fuel pump and sock a few days ago, and I've been driving the truck ever since.. It's like night and day difference. My old pump was reading 8 psi and the new one is pumping a steady 11 - 11.5 👍 The driveability is so much better and check engine light has not come back on. I'm hoping it's a problem solved for good. Thanks again for all your help! P.S I actually just came across another square today in my, neighborhood. 87 just like mine but it's a 3500 1 ton dually. 4 speed 350 truck. Only downside is its 2wd. I made an offer for 2 grand today and he really looked like he would take it and then he said he would do 2500.. so I'm hoping I can bring em down to my mark and score on that one too!
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Sincere thanks for getting back to the forum with results! 8)
So many times it's "radio silence" after a lot of efforts to help out. ???
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Of course man no problem! The advice and efforts to help are so appreciated on my end for anyone to take the time out of there day to even respond to my post. So I feel like you should always respond after a possible solution. After all that's why people try to help anyways, is to make an attempt to solve the problem right? So it's gotta feel good to actually hear back that you help someone. And to me that's is very helpful and much appreciated. Thank you guys all again 🤜🤛👍