? on an old truck

Discussion in 'The Lounge' started by rolland, Feb 11, 2009.

  1. rolland

    rolland Fishing Noob

    I have a 89 1/2 ton GMC with the 4.3 2wd. I barley ever drive it but resently it has got a hesitation in it when I want to give it gas. I stuck some fule injection cleaner in there and it did not seem to help. I am leaning toward it being the fule pump, reason for my conclusion is it runs fine when I start it up and run a few miles but as soon as it heats up good I start to get the delay. To best describe it say im in 4th gear and I hit the gas it putt putt putt... then kicks in. It deffinitly seems like a fule problem not getting to the engen steady. Anyone agree with me or have any other ideas id love to hear em, the fule pump in these are on the top of the fuel tank and not really an easy fix.
  2. before you dive in to the pump.

    A warm engine will run smoother on a lean mixture than a cold engine. If you had a low fuel pressure issue, I'd bet it would be worse before the motor warms.

    Check the mass air flow sensor.

  3. I would change the filter first. Bet its plugged with rust. A bad pump will plug one and its easier than the tank thing. Its a TBI inj so it only needs 10psi on it to run. Pretty tough to plug it enough but...Its more forgiving than the Multi-port that run at 50.
  4. take a flash light ,,with the air cleaner off check the spray pattern of the injectors I will bet one is bad or both
  5. I had a similar problem on a 81 Cougar...turned out to be a plugged catlytic converter...Not cheap to replace......
  6. rolland

    rolland Fishing Noob

    I changed the air filter, never thought of the fuel filter. Ill go check the ports and report what I see in there. It cant be the catelitic coverter, I bypassed that when I put the new engine in it a few years ago. Tks for all the replies so far.
  7. I have a GMC van that is notorious for distributor cap problems. The symptoms are somewhat similar to what you described although it does not usually change when the vehicle is warmed up. What it does is only miss (at least to a noticeable level) at a certain RPM. Above or below that RPM and all is fine. I was told it has to do with the lower voltage output at those low RPM levels causing a weaker spark. I would suggest to at least take a look at the points on the distributor cap and make sure they don't look burnt/corroded. It could be totally unrelated to this but with as many times as I have had to deal with it on mine I know I will never rule it out in the future with any problems incurred.
  8. I Fish

    I Fish I am what I eat.

    I have a 91 S-10, and had an 88 1/2ton that had what sounds like the same problem. Their fix was a new oxygen sensor. I think there is a way to pull the code with a paper clip put into the data link under the dash, I think it's A and B, but I'm not sure. I would ask a mechanic that knows before I would try that. Anyway, after you do, you count the flashes of the "check engine soon" light, and that number corresponds to the problem listed in the manual. I won't be home until this weekend, but I'll see if I can find the manual. That would tell you the trouble code, if it's electrical.
    I've had a couple fuel pumps go out, and it meant the truck didn't run at all. They ran fine when they were shut off, but wouldn't restart.
  9. rolland

    rolland Fishing Noob

    I looked and both injectors seem to be fireing fine, I see the fule hitting the choke even on both sides if its the right PSI I have no idea but they are both squirting fule at an even rate. . The fuel filter looks bad, old, rusted on the outside its deff had some miles on it. Took the air filter asembly off and it still seemed to hestitate when I gave it gas but its tough to tell when not driving it.
  10. When its dry spray the lines down on the filter. They are a pain! 5/8 and 13/16 wrenchs work well. If it looks bad it is bad! It might be droppin fuel press on throttle up. Makes it pop and hesitate. Anything else will kick on a light for a service code and I think it is a and b. Your just grounding the self check. Ya got too start at the begining. Filter first!
  11. Have you ever changed your plugs? I'd replace the fuel filter too if you don't remember when it was done last. It has been recommended before to me to replace them every 2-3 oil changes because the little mesh screen on the sending unit in the tank will wear away. I think yours should be on the drivers side frame rail under the drivers door. That is an easy fix, after you wash off all the gas you're going to spill on your arms. Like said before, I wouldn't change the fuel pump without verifying it is bad...you can test fuel pressure. If there isn't a fuel pressure valve you can always add one up by the intake manifold somewhere. If you have a hard time getting to the pump and sending unit, I've found it easier to remove the bed bolts and prop the bed up with a few 2x4s and save your back the trouble of hunching over the tank. Does your truck have an ECU with a simple throttle body or is it carburated? I had a 92 Chevy with that motor and ended up swapping it out for a new 350 crate motor with a Tuned Port Injection. That truck got-r-dun for lack of a better phrase. Those trucks had a problem with the distributor being located at the back end of the hood, water would drip down when it was raining and would corrode the cap and wires. It would only usually act up when it was raining outside...so it doesn't sound like your problem. But if you haven't checked it out before it would be worth a look while you're in there. If you find it's good, spray the whole distributor with WD-40 and it will make the water bead up and roll off easier. You could use diaelectric grease in the plug wires to keep moisture out also.
    Last edited: Feb 11, 2009
  12. Check the vacc lines going to your map sensor;)
  13. Unplug the vacuum hose from the EGR valve and drive it. If the hesitation is gone you need a new EGR valve. There is an internal bleed in the valve that gets plugged up and allows full vacuum to open it instead of being regulated by exhaust back pressure. The EGR valve is round and gold colored. It sits right behind the throttle body and in front of the

    If that fixes it replace the valve, don't just leave it unplugged. EGR gasses lower cylinder temperatures and emissions, running an engine for an extended period without it can cause detonation and piston damage.

    Hope this helps.

  14. rolland

    rolland Fishing Noob

    found it. The Distributer cap was toast. Coil wire was also bad. Got the parts off my old motor that I had put on there not long before the moter blew and boom, perfect. Thanks a ton everyone went from planing on spending a few 100 bucks on filter/pump/lines to a simple free fix. Looks like im closer to that fish finder then I thought!
  15. ress


    As a start, remember that ethanal blended gas breaks down and draws water. If it has set for some time,2-3 months, the blended gas will be crap. Either drain the tank or, take thefuel hose off at a point where youcan watch it go in a can and turn the engine over. Shouldn't take too much to decide if it's got water. Just a shot, happend to me and that's what we did.
  16. Chalk another one up for the faulty GM distributor cap. I can say I called that one but not because I know more about auto repair than everyone else. It was just because I have been through it enough times myself.:(

    It is always a great feeling when you can save big bucks like that on repairs.