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I have a 1999 Chevy s10 with a 4.3 v6. It has 159,000miles and started missing several months ago. When it first started missing it would only do it occasionally on the highway with light load (65mph on flat ground) but it is now getting worse. With the engine warm it does it under light loads and also when the rpms are high but not under a load (like running them up on flat ground and not shifting right away). The one morning this week I jumped in it and drove cold (30-35
degrees) because I didnt have time to warm it up like normal. The only time it didnt miss was under medium load otherwise it bucked like i was riding a bull and got better as it warmed up.Now for the wierd part, it has not had a SES light on at all for this issue. It starts up right now when you hit the key (indicating to me atleast that its pretty much in time). I was having a fuel issue several weeks ago but when i tore it apart i coulding find anything leaking, so i replace the FPR just incase. I also resealed the intake manifold as it was leaking coolant and oil. While i had the distributor pulled i didnt notice much if any play although it did have quite a bit of thrust play (not sure if that is normal) The contacts on the cap looked a little wore but not extreme.
I replaced all 6 spark plugs a week ago with Ac Delco Iridiums but that didnt help, i have the wires that have yet to be installed. Neither have been replaced since ive owned the truck and ive put over 50,000 so reguardless they are pretty whooped. I didnt mess with the cap or rotor to this date yet because they were replaced about 45,000mi ago (however im not sure how long they typically last. I did purchase a cap and rotor and will see if that helps the issue.I know my fuel pressure is a little low @ 55psi but when its warm it runs awesome under load, no misfiring at all. Which doesnt mean it still cant be fuel.
Any insite would be greatly appriciated! I wasn’t worried too much about this problem but lately it has been acting up more and more…. the last thing i need is to be sitting on the side of the road in the winter.
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Your fuel pressure…is that running, or key on, engine off? Vortecs are very sensitive to fuel pressure. My 5.7 would not start without priming (dumping fuel into the throttle body) at 51-53 PSI. If I recall correctly, spec is around 60.
Have you checked for vacuum leaks? You would think that would trigger a P0174 or P0171 code, though
From what little experience I have, it sounds like fire from your description.
Fuel pressure with key on is 57psi and at idle it is 53psi. Im just afraid if i go buy a new fuel pump the problem wont be resolved. I have sunken alot of money into this truck over the last year and fuel pumps for these are expensive.
I have a freind who owns a sonoma and he replaced his fuel pump due to the sender not reading anymore. I wonder if i could take the sending unit off mine and some how rig it up to his pump and save some money? I would however have to hook it up and make sure that it makes the 60-66psi i need or im not going to gain anything. Atleast if i could make something work for $30-40 it would be less of a loss if the fuel pump wasnt the whole issue.
I have not checked for vaccum leaks but I will once I get a chance. Any other ideas as to what may be the issue?
sounds like your on your way,a good basic tune up plugs cap&rotor and wires,if you still have a miss start checking for a vacuume leak as a vac leak ccam mimmick a ignition missfire.
I have had some vortec engines that missfire on anything except acDELCO parts ,my two 5.7 vans wont fire right without delco cap&rotors in them…good luck!You might try looking for just a pump motor, not the whole pump module. I replaced just the motor in my Neon pump module for $22 and it came with 2 new fuel strainers to filter the gas before it came into the pump motor from the tank. Just a thought, kinda like what you are proposing with the purchase of your friend’s old pump assembly.
Replace your fuel filter if you haven’t already. It may not solve the problem but chances are it needs to be done anyways, and they are very inexpensive.
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