1988 chevy c3500 5.7l 350 sm465 4 speed manual
Recently had a miss when vehicle warmed up but fixed it after replacing dist/rotor/
button/ig. coil/pickup coil/wires/spark plugs/IACV/TPS/fuel pump/fuel filter. But hidden
under all that is a new or exisiting problem I didn't know about. Truck runs fine cold/
warm and shifts thro all gears and has plenty of power. Just at 60+mph it sounds like it
wants to go into OD but doesn't and there is no power then till u let off gas and let it get
back down to ~60mph. Please help, thanks.
Low fuel pressure? Test your fuel pressure at idle and under load. The regulator in the TB may need attention. Note: The ICM in the dist is usually what I go to first. It likely would not cause this issue but just keep it in mind as everything else is new it's prob next.
Yea when I replaced the distributor it came with a new ICM and pickup coil already on it. I did rebuild the TBI alrdy. Forgot to mention this. Was tired at the time. It only happens at 60mph+. Its driving me nuts. I'll check fuel pressure to make sure its where it should be but I had just replaced the fuel pump because it had died the one day and wouldnt start up so I tried the fuel pressure and had none. Just seems its one thing after another lol. Slowly getting it sorted out. The truck had sat for ~6 years before I got it. Ran good for a week then all these little problems popped up.
The regulators cause problems occasionally. I think jegs is the one that has a decent aftermarket rebuild kit that lets you adjust the pressure if interested. I think the target is between 11 and 13 psi. When you rebuilt it did you check replace the injectors? The 4.3 through 7.4 use the same throttle body and injector body size, the different displacements have injectors with larger flow rates. If you replaced the injectors they may be to small leaning you out at load. If the pressure is good and the injectors or correct I'd be stumped for now. If you've invested that much into the truck you must like it? I would recommend getting a scanner to read live values. We are pretty limited on hand-helds due to being GM OBD1. I use a ALDL to usb cable and my laptop. Got it on ebay for 70.00 and can talk to most OBD1 vehicles with free software on the internet. You would be able to see all sensor inputs, ECM outputs and codes. Works with most GM OBD1 ECM/PCM's.
Pretty sure I need a new fuel pump again.... pretty sure it will solve my issue. Just put a new one in and it only has like ~150 miles on it..... sad...
Ok. Got a new fuel pump... dropped tank and pulled the other new fuel pump out and noticed my fuel sock was alittle aged, to put it mildly, and had some tears starting. Here the inside of the fuel sock was shedding pieces off and they got stuck in the fuel pumps screen choking the gas flow. Ran on down to auto parts store and replaced it and now all seems fine. Now I need to put some more miles on her to see if everything is all cleared up. And for ur earlier post, I do love this truck and need it for towing/hauling but nothing too serious. I need to replace manifold gaskets, clutch and some other odds and ends... nothing too serious. Thanks for the help :D
Glad to here you got it running good again.
Now I have 3 codes, 13, 32, 42. I would think 42 is my most pressing one. IC error, from what I read it hooks up to the ICM and it might be grounding out somewhere. I tested the EGR, by pressing the diaphragm in and holding finger over the hole to see if it leaked or not. Might need a new one I don't know why its throwing that code. And as for the 02 sensor open I don't know if it has to do with the exhaust manifold leaking or if one of the sensors needs replaced.
The codes don't always mean that the exact part or sensors is bad, it just means that the ECM is not seeing a value that it should for a certain input. 42? your new parts may not be playing nicely. You can check new dist assembly that you installed to make sure everything is good. The plugs from the coil and wire-harness and the pick-up. Ensure that the ICM has plenty of heat sink component between it and the baseplate. As for the other two codes they are most likely caused by the O2 alone. A '88 should only have one single wire sensor, check to see that the wire didn't get broke or melt to the exhaust. This is why I like seeing the live values as the engine is running, I don't even look at the codes unless I can't see the issue live! You can trend the inputs looking for spikes or weird values.
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