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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: Scaryfastatx on April 03, 2024, 09:22:46 pm
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Hey all, before I start tearing into the fuel system. I'm having a head scratcher
Truck details, 305, dualjet M2ME, TH350, 4.11 gears
My truck had been running like a champ, then all of the sudden started getting some random hesitation mostly during higher speed cruising usually between 2k and 3k rpm
I lift and most of the time it comes back but refuses to go faster, in a few cases it's died at idle. It will start right back up with some throttle input so pretty sure it's a lean hesitation.
I noticed the vacuum pull off died so relaxed that and it was back to normal until it reached 3k. Next day got worse. I adjusted the carb according to a manual I found online for a 78 dualjet.
Started and idle was perfect, at no load and heavy throttle it was fine, but again higher speed cruise it stumbles
It's a brand new carter mechanical fuel pump, new carb filter, added an inline filter on the frame rail where the girl lines go across the bed.
Carb has not been rebuilt
Any common stuff on these to look for first?
I was gonna start with plugging the return line, then check the filters and then the check valve in the fuel inlet
Thanks!
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Steady speed cruising, acceleration at that rpm? What do the plugs look like?
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Sounds like ignition.
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Steady speed cruising, acceleration at that rpm? What do the plugs look like?
From a stand still it pulls hard up to the speed limit, but then starts sputtering
But I'll adjust the carb to limp home and the point where it sputters move around
I'm gonna pull the plugs this weekend to check them
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Sounds like ignition.
Think so? Like the module starting to give up?
I have a coil from my old Pontiac I'll swap it and see
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What year? HEI? Points?
How long has it been since you replaced the ignition components?
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What year? HEI? Points?
How long has it been since you replaced the ignition components?
It's an 81 and has HEI, it has new plugs, wires and cap and rotor but the rest I have no idea been a while
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So your Pontiac coil is HEI too.
Well, give it a shot.
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Well tried everything, cracked open the carb cleaned it all out, rebuild it and set the float up a little
New filter, swapped ignition
Still lean hesitation and it's getting worse
Today I capped the return line and it's starting up and idling with the choke much better
Starting to think my brand new Carter fuel pump is the culprit
Who makes a decent pump not made of Chinesium?
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None of the names we've grown up with, we gave it all away. :(
Delphi is about the closest thing to quality....
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None of the names we've grown up with, we gave it all away. :(
Delphi is about the closest thing to quality....
Sheesh, all in the name of corporate profits
I'm gonna pull the trigger on the Delphi one and see how it goes
I went for a little cruise with my kiddos just now and it starts up and idles much better with the return line plugged
If I accelerate hard from a stop it runs strong until like 30mph then stumbles. I let off for a bit and runs good again
If I accelerate normal it will go up until 50 then hesitate
Pretty sure it's the pump not giving the flow rate needed for the carb
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Or the rubber at the tank end is split, and sucking air, or soft and sucking shut. The amount of ethanol in todays gas is high, and not very rubber friendly.
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Or the rubber at the tank end is split, and sucking air, or soft and sucking shut. The amount of ethanol in todays gas is high, and not very rubber friendly.
I actually replaced all the hoses when I replaced the tank.
I used the stuff rated for alcohol
BUT I actually found a gas station here that sells ethanol free, so that's all the truck and my other old cars get
It's a dollar more per gallon but worth it not to be tearing into the carbs all the time
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I remember the days of changing out ignition points and the condenser. Long gone!
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I remember the days of changing out ignition points and the condenser. Long gone!
I still have a 1966 Gem, stock points/condenser combo. Still use my dwell meter... ::)
I know I know, In time I'm going to upgrade to HEI or MSD.
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Or the rubber at the tank end is split, and sucking air, or soft and sucking shut. The amount of ethanol in todays gas is high, and not very rubber friendly.
I actually replaced all the hoses when I replaced the tank.
I used the stuff rated for alcohol
BUT I actually found a gas station here that sells ethanol free, so that's all the truck and my other old cars get
It's a dollar more per gallon but worth it not to be tearing into the carbs all the time
I'm jealous! ;)
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I was shocked to find it to be honest. But all the Quick Trip gas stations here have it now. So I get ethanol free for my truck and the lawn mower haha
I'm jealous! ;)
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So today worked on the truck more still haven't found the problem, getting really frustrated
I'm thinking maybe it's the vacuum lines
(https://i.imgur.com/AfRUXJN.jpeg)
So I pulled everything and wanted to rerun them with new lines
My big question is, where does the vacuum advance hook up? The ports aren't labeled on my diagram
I had it originally hooked up to the port on the base plate, but read on another form for G vans where the guy had a dualjet and his distributor was connected to port B
(https://i.imgur.com/bMUNLWN.jpeg)
Thanks
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So obvious question: Is smog compliance still part of your truck's existence?
If yes, then keep digging.
If no, then apply direct manifold vacuum.
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So obvious question: Is smog compliance still part of your truck's existence?
If yes, then keep digging.
If no, then apply direct manifold vacuum.
It's not smog compliant, it's older than 25 years so they don't make us test them anymore for inspection
So is the port I need to connect to the lower passenger side one?
(https://i.imgur.com/UwoneXh.jpg)
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My understanding is that all ports on a carb are metered except the EGR.
Direct manifold vacuum bypasses that.
Look for, or create a port that goes directly into the intake manifold.
If you have an automatic transmission that has a vacuum operated modulator, that would be a good source to tap into.
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Well I got some time today, and put my vacuum gauge on the ports
Port B is full manifold vacuum and port on the bottom passenger side is ported
Fingers crossed that does the trick
(https://i.imgur.com/UwoneXh.jpg)
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Well, I don't know what else to check
On vacuum port B it felt a lot better with the full manifold vacuum
But got it out on a more open road that I could get some speed and it's still cutting out
Usually at higher speed
If I downshift and get to the rpm where it's stumbling it seems fine
Also if I go really light on the throttle up to speed sometimes it will go faster and maintain the speed
But it's intermittent and will also stumble sometimes
But if I go heavier on the acceleration it stumbles quicker
Other times it stumbles at really low speed
I'm really confused and frustrated
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Have you inspected the spark plug electrodes and checked the ceramics for cracks or carbon tracks? Check the spark plug wires for hard spots especially where they route near metal edges and the exhaust manifolds. Use a bright flashlight to look up inside the spark plug boots and the distributor boots for black soot or green discoloration. Inspect the cap & rotor for black carbon tracks and cracks.
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Have you inspected the spark plug electrodes and checked the ceramics for cracks or carbon tracks? Check the spark plug wires for hard spots especially where they route near metal edges and the exhaust manifolds. Use a bright flashlight to look up inside the spark plug boots and the distributor boots for black soot or green discoloration. Inspect the cap & rotor for black carbon tracks and cracks.
I'll check it out
The plugs and wires are basically brand new
I thought for sure it was either fuel or timing but seems like those are fine
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I think I may have cracked the case!
I was reading through the service manual about engine cut out at higher speed and it had a procedure to do pump down on the fuel lines to see if it is sucking air
So I have a fuel filter in line where the lines cross the bed and go onto the frame rail
I pulled it and did a pump down and it read ~14in Hg
(https://i.imgur.com/miLv3b6.jpeg)
I then was going to lower the tank to tie my vacuum gage in when I saw this (fairly new yikes)
(https://i.imgur.com/TMdUp8W.jpeg)
Once I dropped the tank completely looks like there was some minor leakage on the fuel feed line, so definitely was sucking air
(https://i.imgur.com/EWSg8IN.jpeg)
(https://i.imgur.com/Nb0OODU.jpeg)
So I put my lines back on and pumped down and it's looking great
Think I may have cracked the case
(https://i.imgur.com/BOVqgYS.jpeg)
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Todays rubber is doo-doo.... :(
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So when will we know Mr. Scary??? Great detective work BTW. ;D
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WELP!
that was not the problem. I ordered some clear gas approved tygon tubing and a tee fitting, gonna check for bubbles, flow and pump down
Also thinking to swap to an old Edelbrock carb I have just to do a comparison and see if maybe something is wrong with the carb that the rebuild didn't fix (power valve?)
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https://youtu.be/hCZ_xpEzpoM?si=hVvwvJLpUs1R86FU
https://youtu.be/S5igtSmeQI8?si=a9ofp4CSbUAeODge
Brand new Delphi pump has a bad return valve
So frustrating
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If you've validated your fuel volume and that there is not a feed issue, replace the ignition control module.
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If you've validated your fuel volume and that there is not a feed issue, replace the ignition control module.
It's a brand new GM module in the hei, the rest of the ignition is new as well
Pretty sure the pump plus the leak at the tank was the cause of my issues. Gonna get the Delphi warrantied and throw the old Carter I had back on there and see what it's pressure looks like
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So the seller on amazon refused to warranty the Delphi pump, Amazon told me to call Delphi, they told me to email them and I got a 1 line reply, warranty through reseller, we dont deal directly with consumers.... GREAT JOB amazon! well fool me once
I got a new lifetime warranty pump from Orielly and slapped it on, and fuel pressure is now pretty constant, jumps between 6-8psi, revving it up drops to 4 but never below
no bubbles in the line
but took it for a ride and it would not stay running for long
I was thinking and thinking about it, and had an idea to check the power piston, maybe the spring is too weak and the rods are staying down in the jets
so I pulled the carb today and the spring is stretched out and the seal is super worn
https://imgur.com/QY1z28p
(https://i.imgur.com/kvs8rfr.jpeg)
(https://i.imgur.com/TRmgvIt.jpeg)
(https://i.imgur.com/y0vKOqe.jpeg)
gonna address that, then maybe see if tweaking the APT setting
fingers crossed!
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Good luck bro!
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With the new spring in the power piston, it still is dying
So after thinking a while it popped in my head to check the float level before and after it dying
In the driveway is idling and revving like a champ
So here is the float level at idle
(https://i.imgur.com/SReRjYf.jpeg)
~4.8cm (~1.88in) from float to top of the air horn, pushing down I can feel the float bob and smell the gas
So drive it around and after just a bit it dies
Here's the float level Dead on the side of the road but cranking
(https://i.imgur.com/R9ye4yV.jpeg)
~5.3cm (~2.08in) from float to air horn
So definitely a fuel supply issue still going on
Right now I have 3 filters
1) long filter in the carb
2) aftermarket chrome filter on the frame rail
3) sock in the tank
I'm gonna pull the filter on the frame since it's the easiest to get to, see what that does
Then move to the filter on the carb
Then finally drop the tank and check the sock
It's a brand new tank and sock gonna be so pissed off it's the sock
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I'd start with the one in the carb....what are the odds that it's upside-down, and the check ball is having it's way with your sanity?
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I'd start with the one in the carb....what are the odds that it's upside-down, and the check ball is having it's way with your sanity?
Yeah good idea
I've noticed that these new filters get rusty really fast, even with ethanol free
Wonder if that's blocking the filter too
Gotta love old vehicles!
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Isn't the check valve/ball at the entrance of the fuel inlet?
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Isn't the check valve/ball at the entrance of the fuel inlet?
yep, it has the little plastic plunger type check valve in the middle of the filter body
(https://quadrajetparts.com/images/thumbs/150_150/GHP-Q2253CV-w500.gif)
my gut is saying its the sock in the tank.... which Im kicking myself for not looking at it when I had it dropped earlier to replace the lines.... LIVE AND LEARN
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Isn't the check valve/ball at the entrance of the fuel inlet?
I've seen it installed upside-down about 10% of the time.
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With that many filters, I'd delete the carb filter and see what happens. If still choking, delete the inline. Of course, if still choking, you will be left changing your sock, like out moms told us long ago... ::)
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Ive been working on other projects, but finally got back to the truck this morning. I decided to cut open the filter to see whats going on. I dont know why I hadnt thought of it in the past, just always checked the check valve plunger to see if it would go into the filter body.
But yikes, I am really glad I checked it out
(https://i.imgur.com/ymDj55G.jpeg)
(https://i.imgur.com/vZsmzi6.jpeg)
new filter is supposed to be here today.
Im guessing there is a lot of trash in the lines, all my fuel hoses are new, new tank, new sender, new pump.
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Now, aren't you glad the filter did its job? :)
Before the incorporation of check valves, you could simply blow through the filter to determine if it was plugged.
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Now, aren't you glad the filter did its job? :)
Before the incorporation of check valves, you could simply blow through the filter to determine if it was plugged.
haha yep, that is exactly what I thought, I just rebuilt the carb, wouldnt have been fun cleaning out all the trash again.
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It would be prudent to disconnect all of the lines and blow them out from the tank forward.
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Found the source of all the trash in the carb filter.... drumroll
It was my Mr. Gasket chrome in line filter
(https://i.imgur.com/yNvpvcn.jpeg)
looks like the glue holding the filter media to the canister and the end cap didnt like gas, it completely came apart and the filter media was rattling around inside the canister
(https://i.imgur.com/w5rKGkx.jpeg)
(https://i.imgur.com/6ldDdAC.jpeg)
(https://i.imgur.com/Z10MJd3.jpeg)
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The ethanol gas is just nasty when it sits for any length of time.... >:(