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Thread: TPI Firebird stalling, misfiring

  1. #1
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    TPI Firebird stalling, misfiring

    A week ago last Thursday evening I filled up my T/A's tank from the half way mark. Dropped a buddy off and went home. The next morning I picked up my buddy again and got on the freeway. Just as we got on it started bucking (like it was severely missing) and wouldn't rev at all. She stalled by the time I made it to the shoulder. She fired right back up and felt fine for a minute, but stalled again at least twice on the way back home to get my ZJ.

    After work I stuck my fuel pressure gauge on and it took a few tries to get it to idle. It would run for maybe ten seconds then sputter out. Five or six tries and she fired and idled decently, aside from that slight fluctuation. Even while sputtering and dying the fuel pressure acted just like I'd expect, it didn't do anything funny at all and definitely didn't drop out while it was sputtering. My very first thought was the fuel pump but now I have my doubts. No codes thrown at all, no CES light until the engine died (of course).

    Filters, plugs, leads, cap and rotor have all been in for a few years at least but there's less than 10k on 'em. I pulled an easy plug and it looked damned near perfect. I swapped in my old ignition module just to rule that out. It seemed to idle better, although it did still die on me one time seconds after starting. Hoping for the best, I took it for a spin around the block. I made it to the corner, went to give it a little gas, and it bogged down and almost stalled. It felt WAY worse than a single cylinder misfire. So I broughter 'er back home, barely touching the gas along the way.

    It revs okay in neutral, doesn't idle very well, chuggs and stalls occasionally especially right after starting, and wants to die under any load once I touch the gas. I also cleaned the IAC motor (again) for the idling issue but it was still damned near spotless from when I did the intake gaskets last year. Fuel pressure looks fine in park and the one plug I inspected looks great. I couldn't see any arcing on the leads at all when I fired it up in pitch darkness this morning before work. The cap and rotor are nice and clean, little to no wear.

    I'm running out of idea with this damned thing. Bad gas? Fuel pump crapping out under load? The gas station tells me that they've had no other complaints, not that they'd tell me if they had. What else should I be looking at? All I can do is guess at this point.

    Stupid GM's. My Olds is acting up too. Ugh...
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  2. #2
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    depending on the year, you just need to short out the test pins on the harness under the dash, it'll flash you a code when you turn the ignition to ON without starting. Some codes dont throw the service light on, check that first.
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  3. #3
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    Try a TPS sensor first if that don't work try a Map sensor mine have went before and not set codes.
    Tim

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    Codes were the first thing I checked. It only had a code 12. Normal, since she wasn't running at the time.

    I'll check the values on the TPS, and I think I have a spare MAP sensor I can try. I also have a spare coil that I need to give a fair shot.

  5. #5
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    Get the gas out and put in new from a different station! I had the same problem with my car and it turned out to be bad gas. once there was new gas in her she ran like new again!

    just my 2 cents!

  6. #6
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    efore you go spend a fortune on new sensors, check the vacuum hoses, had mine come off the MAP and ran like crap

  7. #7
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    Vacuum hoses look good (aside from the EGR line, which is under the plenum and damn near inaccessible to check). I've sprayed carb cleaner all over that intake looking for any sort of leak. I also pulled each plug lead while running one at a time (got a couple of zaps, even with insulated plug-pliers) and each one dropped the revs by about the same amount, nothing stood out there.

    The sensors I've tried haven't cost me a cent, I had them laying around.

    I think I'll try that MAP again since I don't remember it crapping out with the spare one, but otherwise I think I'm back to looking for 60L worth of cans.

  8. #8
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    sounds like you should throw a Hamilton meet and greet and bring a jerry can at your house

  9. #9
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    lol Not a bad idea. I do have most of a 28 of Bud in the fridge in the basement...

    Just for the hell of it I unplugged the temp sensor (the one on the intake, not the one on the head for the gauge) and fired it up. It settled into a nice idle. CES light was on of course, but no sputtering. I shut it down, plugged it back in, fired it up, and it quickly sputtered out and died over a few seconds. Unplug the sensor and try again, nice steady idle. Son of a bitch, could it really be as simple as a $15 coolant sensor?

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    if you got a zap through the wires you need new ones. there breaking down and arcing to ground. dsnt matter how many klms are on them. gms have a verry powerfull ignition system and a good set of wires are a must. check for small white spots on the wires this is a shure sign the fryed.

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    I did the same thing, unplugging a sensor that is. Engine running like crap, hard to start, no power. I started unplugging one at a time, found one that made a difference and left it unpluged. Damn thing ran smooth for a year, then I sold it. I think it was some sorta air temp sensor. I never looked into it.

  12. #12
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    Ah, I worded that poorly. I only got zapped while pulling the leads from the distributor on the engine while it's running, not from just handling the leads. I've found no breaks, burns, or sparks in the dark from the leads at all.

    I plugged in (but didn't install) a new temp sensor. No change, it still dies out. I unplugged the MAP and it idles fine, just like unplugging the CTS. I unplugged the TPS and it idles high, at around 15000 rpm. TPS voltages check out and looks smooth. My injectors though, they ohm all over the place. All but two are out of spec, they're on the shopping list. Could flakey injectors cause my sudden problems though?

    And why in the hell are my headlights suddenly popping up (but staying unlit) with my running lights? Coincidence? Haunted?

  13. #13
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    take a couple of wires off and check the resistence through them if any of them are more than 7 oms junk them. not sure about this but if you unplug a sensor the computer may have a limp mode where it runs the fuel injection on a set program and ignores some of the input sensors may be why it likes to run with somthing unpluged.

  14. #14
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    My buddy and I went to Standard Auto yesterday for the free-parts-day. We grabbed a set of injectors out of a late 90's Town Car. They look to be almost ideal, they all ohm very close together and they all seem to work (I ran a little penetrating oil in 'em overnight to check for leaks, and they only dripped once I pulsed them with 5v). From what I've read they should drop right in once I find a set of o-rings, pintle caps, and hopefully basket filters. My old injectors may not be THE problem, but they're definitely a problem. Worth a shot.

  15. #15
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    Sounds to me like when you are removing a sensor, the ECU is going into open loop and thus using the default maps in the computer, sounds like you have a sensor that is flakey but not gone enough to force an open loop condition. That's why removing one entire sensor seems to fix it because it forces an open loop condition.

    If you have a scantool, i'd plug it in and see what things look like. Is there a CPS on that engine?
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  16. #16
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    Yeah I assume that it's going into a limp mode with the CTS or the MAP disconnected. Why it revs at 1500 rpm with the TPS disconnected I have no idea. I don't think it's an open-loop/closed-loop issuse since it acts up when stone cold. If there is a flakey sensor it's also not flakey enough to throw a code. That's why I'm concentrating on the injectors right now, if they're acting up (like these nearly twenty years old Multecs are known for) then they aren't helping matters if not causing my problems altogether. I vaguely recall reading that it fires all eight injectors together when in limp mode versus four at a time in normal operation, although I could be mistaken. Either way, the injectors are old and need to be swapped out.

    It's an OBD1 system so no CPS, and I unfortunately don't have an OBD1 scan tool. Just my trusty cotter pin for checking codes.

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    Alot of GM Cars from that vintage would bump the idle to 1500 during open loop to help it stay limping (instead of dying which it would do when something was wrong at regular idle).

  18. #18
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    Really? Makes sense I guess, although that would make putting it in gear a little hairy.

  19. #19
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    Well I disconnected the CTS and ran it just long enough to turn it around and back it into the garage for the winter. I plan on making the Ford injectors work on my intake over the next few weeks so hopefully she'll give me no trouble in the spring. I just need to take the insurance off and that headache goes away for a while.

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