95 GT running rough

Discussion in '1994 - 1995 Specific Tech' started by 1slow95, Aug 27, 2011.

  1. I just installed a mostly stock engine in my car and can't seem to track down this problem. At part throttle the car feels bogged down, sputters, and sometimes backfires. If I put the throttle down about 85% it will sputter, backfire, then take off and run normal. WOT seems to be ok, although maybe a bit under powered. I cleaned the MAF and installed new O2 sensors but it didn't help.

    Mods are a ported lower intake, shorty headers, o/r h pipe, cam installed at 112 ICL, new timing chain and lifters, EGR delete, all smog stuff deleted, a/c delete.

    I had a vacuum leak at my oil separator that I'm not sure I got fixed. I suppose that would be the next place to look :shrug:

    Plugs, cap, and rotor are supposed to be new. They all looked fine so I reused them. Plug wires are good. New fuel filter. Fuel pressure set at just under 40 psi. Timing is around 12°.
  2. I think I tracked it down to the EGR delete. Tried it with the EGR sensor thing unplugged, plunger halfway, all the way out, and all the way in. It runs terrible with it unplugged and best with it halfway. So now I need to decide between buying new headers and EGR stuff, or just getting a chip to tune it out. Or I could go back to my AEM, but that would be a bit overkill :).
  3. You replied to yourself but I was going to tell you about the EGR plunger. Had the same issue, there was thread a few years back on this and everyone did the half way in trick. Had mine laying on the top of the tranny backside of the intake. Worked like a charm.
  4. Well what I found was that the ecu still thinks the egr is there and functioning if you set it with the plunger halfway. It looks like the ecu pulls fuel at part throttle because of the exhaust gas coming in from the egr... So with no egr the engine will go lean and backfire, which is exactly what's happening to me. I also remember my car doing the same exact thing when I first installed the 420w, and it stopped doing it right after I installed my mail order tune. I always thought it was just because the car was not tuned, but I guess it was the egr delete.

    Im going to hook up my aem tonight and do some tuning just to make sure it's not a mechanical problem. Then I'm thinking I'll go with the moates F3 and jaybird so I can disable the egr and make a few tweaks to the tune.
  5. Well it's definitely in the tune. Installed the AEM, loaded the base tune, and tweaked it slightly to set the idle. First test drive and it's running much better. The low end power and throttle response is 100x better. I don't have wideband installed so I couldn't really do any tuning. I could tell it's running rich, plus the stock O2's were pegged rich.

    Do you think it would be worth it for the Quarterhorse over the F3 chip and burner? If I had more mods I would definitely go with the QH, but I only plan on disabling the EGR, tip-in retard, and maybe tweaking the timing a little. Price difference is about $100, and the main functionality diff is the QH has data logging and live tuning.
  6. mine has some hesitation problems that I was attributing to the MAF, but even with it cleaned it still kinda hesitates when I floor it. I have my EGR deleted with a plate, all vacuum lines deleted and the header capped. Could this be my problem as well? I might try and plug the EGR sensor in and tape it halfway like I've see posted a few times.
  7. Mike, were you logging a hard-fault EGR code?
  8. I kinda forgot to check the codes. I'll get the stock ECU reinstalled and pull the codes.

    Mark, it's my understanding that if you delete the EGR but don't disable it in the ECU it will cause a lean condition. In my case, half to 3/4 throttle acceleration would stutter, pop, and hesitate. Going WOT would hesitate for a second then run normal. EGR is not active at WOT, so that pretty much confirms it for me.
  9. well I taped up the old EGR sensor and I'm gonna see if that helps. I've heard 50/50 on those little things you get from Ebay that supposedly gets rid of the EGR CE light. I'm going to get a tune but right now with it N/A I'll deal with it. I can go about 300 miles on a tank of gas on the highway which is good I think.
  10. Well I drove 150 miles just now on the interstate and no CE light! The motor seems to run smoother and has way more get up and go!
  11. Mike, this is why I'm asking. AFAIK, if you DO (did) have a hard EGR fault, the EEC shuts off the EGR function in the EEC (because it knows there's an issue) and the car should run ok.
  12. Checked the codes:
    334, 172, 177

    It's odd that 172 and 177 happened together...Bank 1 lean, Bank 2 rich. The car was running very rich with the AEM so I'm guessing that did something to the O2's. Hopefully it will clear up after driving it a couple times. This is the first time the CE light has come on since I installed the engine, and the only change was running it with the AEM for a short time yesterday.
  13. Got my Moates QH today and did some tuning. Disabled the EGR and that made no difference. So then I forced it into continuous open loop and it ran right. The only difference between OL and CL is that the ECU is adjusting A/F based on readings from the O2's in CL? Since I replaced the O2's, the only thing I can think of is it's a problem with the wiring where I extended the wires when I had LT's... Any other suggestions?
  14. The thing with one bank being lean and one rich was weird anyways. I guess I'd double check the wiring and output of each O2, as you suggested Mike.
    Forcing the OL with the LT's is probably not a bad idea anyhow.
  15. I don't have LT's now, but I did on my last engine.

    I just thought of something and I feel like an idiot. Does the ECU adjust bank 1 and 2 separate? Because now that I think about I'm pretty sure I have the O2's plugged in backwards. I'll swap those when I get a chance and report back.
  16. Well apparently my brain was completely fried by the time I installed the O2's. They were connected backwards and the car now runs great with them correctly plugged in.
  17. so are you now thinking or wondering if your problems with the big motor were related to the O2 wiring problem? i didn't read the whole thread, so if you answered it already, sorry
  18. Nah, it was partly O2 related when I had the stock ECU installed. Mainly because the adaptive learning would cause problems after a while I think. The AEM ran off a single wideband, which I had installed in bank 2 but plugged into bank 1. That's why I plugged the stock O2's in wrong. I had them tied up under the car backwards and was too exhausted at that point to notice.