Cold start fuel problem.

Discussion in 'Performance & Fuel' started by 00J, Nov 23, 2012.

  1. 00J

    00J New Member

    2000 Jimmy, 4.3L

    ignition coil, dis. cap, rotor button, plugs and wires are all less than 6 months old. I started having problems starting early mornings when frost hits. I just put in a new starter and battery. I feel it's a fuel issue, but scan is only showing P0453 (high tank pressure) and occasionally P0452 (low tank pressure). Both are EVAP errors indicating to me that the pressure in the fuel tank is inconsistent. I've recently been hearing a gurgling noise under the fuel plenum, and need to cycle the key numerous times to build up pressure in the system before it will start. Then once it fires up the gurgling noise stops. Even if I turn it off and start cycling the key again, the noise wont come back until it sits for a while (at least very faint). Once its been running, it will start up time and time again until it sits overnight again. it idles a little rough, but no misfires are indicated on the scan. I'm thinking that possibly it's a problem with the fuel pressure regulator not holding the pressure and causing the fuel to trace back into the tank. My question is, is it possible that it could be my fuel pump itself, and any idea why the regulator would only fail on cold mornings? It seems I can try to start at 5 degrees and it wont start (Cranks fine), I can come back to it an hour later at 7 degrees and it fires right up first try without even cycling the key. Could the bad regulator have fowled my plugs that fast that the cold weather is causing them not to fire? With winter coming I'm hoping to wrap up this issue this week and any insight would be appreciated. thanks.
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    My first thought, rather than regulator, would be the check valve in the fuel pump allowing fuel to leak back into the tank. In any case, I'd probably start by putting a fuel pressure gauge on it to see how long it takes for the pressure to build up and then monitor the pressure to see how quickly it drops off when the pump shuts off.
  3. 00J

    00J New Member

    Thanks for the input, I picked up a pressure gauge and seems the fuel pressure sets at 62 on cranking, and holds eventually dropping down to about 45-50psi after 10 minutes or so. Pressure seems fine in my opinion. I may still have fuel issues (burning rich) but its not whats preventing startup. I haven't even checked my ignition system until today because it was replaced so recently, but I'm not getting spark from my coil (unless I'm testing it wrong) I unplugged the coil at dist. and ground a test light and placed the probe at the tip of the coil wire while a friend cranked and no spark . I've tried doing some tests and couldn't get any voltage readings at all with the switch on from the module or coil. I checked fuses and they seem ok, the switch itself should be fine since the pump is kicking in, and I've been told the ignition mod, and pump run off the same fuse. Any input on properly diagnosing ignition modules? I have noticed however if I put upward pressure on the key while cranking, and push it in with some force that my lights will come on during crank and it will struggle to start, I've gotten it going twice by doing this, but as soon as I turn it off its back to no start. It's just a pain attempting this because its killing my battery, and I need to keep recharging it taking time from trying to diagnose the problem. Possibly ECM or CKP sensor?
  4. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    If it is holding 62 psi while cranking, it probably isn't a fuel issue.

    When I burned through the wire to my CKP, I got a CKP code from the computer. Where you don't seem to be getting any kind of CKP code, I'm not sure I would suspect a CKP.

    Putting upward pressure on the key might suggest a fault in the ignition switch, but then one would not expect the fuel pump to run.

    I haven't had to diagnose the ICM on mine. On other systems I've played with, it has usually been enough to check the ICM for power and ground (because it usually ended up being a fault in the ICM power and ground circuits rather than the ICM itself).

    ECM is always a possibility, but they can be the hardest to diagnose, because you usually do it by process of elimination (when everything else has proven good, then the ECM is the last possibility).

    I wish I had a good suggestion, but I'm really not seeing anything that suggests anything to me. Anyone else have ideas?
  5. 00J

    00J New Member

    Good news is i got spark back the coils firing again and i hear the timing on the 4.3s are pretty well tamper proof as long as the belt doesn't break. i haven't totally crossed of a fuel problem even with good pressure as i think there's a problem with the injectors. the gurgling sound under the plenum is consistent and i noticed after sitting for a few hours the pressure dropped as low as 20-30psi. Not sure if this is normal but after putting the key to "on" it immediately shot back up to 62. Maybe they aren't opening due to a computer error. Ill find some time Monday and pull the plenum off and see what's happening unfortunately i work all weekend so i don't see it happening sooner, but ill have to pull each injector out to see if they're firing.

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