Eggplant Jeff

OK I have been having a cold start problem ever since I bought my car. The engine bogs down as soon as it catches, then it recovers. In colder weather, it bogs down more, and will actually stall in very cold weather. It ALSO bogs down when coming down after revving in drive (I.E. move up a car length in traffic, rev the engine at the guy next to me, etc). I also have a slightly uneven idle that I think is related to this problem, and it takes several seconds of cranking to start the engine.

More recently I have been having a detonation problem, even when running 93 octane at 2 degrees advanced.

I THINK this sounds like a vacuum leak... Other people with TBI say the bogging is what happens when you have a vacuum hose loose. The leak would contribute to my uneven idle and hard starting. And, a leak could cause one or more cylinders to go lean, causing detonation.

However, I have plugged all vacuum hoses and it still does this. I removed and reinstalled the intake manifold because I thought it was leaking there, this also means I put a new gasket under the TBI unit so no leaks there either.

TPS, CTS, EGR valve & solenoid, IAC, ECM, O2 sensor, are new (a year or less old). MAT/IAT, MAP check out fine with a multimeter.

I just put in (with the intake) new plugs (dealer recommended AC Delcos gapped at a stock .035), and new wires (MSD SuperConductors). The cap and rotor are Accel, they and the pickup coil are about a year old. The ignition coil is the MSD GM Blaster, again about a year old. The fuel filter is about a year old as well, injector spray pattern on both injectors looks good to me. Car runs fine at high RPMs so I don't think there's any sort of fuel delivery problem.

I'm running Mobil 1 5w30.

Only engine-related mods I have are a 14-inch open element, ported (ultimate TBI) throttle body, AFPR (right now it's set back to about stock pressure though, higher pressure didn't affect any of my problems). I've got a 180 thermostat and high-flow water pump, but obviously that wouldn't affect starting.

I had exhaust leaks from both exhaust manifolds, I removed them, cleaned the sealing surfaces, and reinstalled with gaskets. No more leaks, but no effect on the above problems.

The starting problem has remained UNCHANGED through ALL of the above! It was there when I bought the car, and it's still there now.

The ONLY two things I can think of:

1) It almost seemed like this problem was fixed when the engine was running like crap because a plug was broken. When I removed the plugs (and found the broken one) I put them back in more gently, afraid that it had broken because I applied too much torque when installing them. I made them tight, but maybe one isn't quite tight enough and is allowing air in past the threads? I tightened them by hand, I didn't use a torque wrench on them, anyone who thinks I should have has obviously never changed the plugs on a thirdgen :-).

2) Someone on here one time mentioned that the throttle shaft (that the blades are attached to) had worn away a little at the throttle body, and so air was leaking past the shaft. If this is the case I guess I'll need a new throttle body. I'm not sure how I can check this easily, spraying carb cleaner at the throttle shaft I'll get a bunch of overspray into the throttle bores so if it afffects engine RPM I won't really know if it leaked in or if it was just the overspray.

Can anyone give me any more suggestions? This is driving me bonkers!

Eggplant Jeff

I forgot to talk about codes!

Currently it's not throwing any codes. It threw 23 ("Low temperature at MAT OR TPS error") for a while, even though the MAT was reporting the correct value. In fact, the ECM was getting the correct voltage at its connection, that's when I replaced the ECM. Haven't gotten the 23 since then though. But, I more recently got a 21 ("High voltage at TPS") which can be caused by an open ground wire. I figured out that the plug wasn't making good contact with the TPS sensor, so this may have caused the earlier 23 as well. I also (on my way to Autozone to get a replacement for the broken spark plug) got a code 15 ("Low temperature indicated at CTS") which I have no idea what caused. I pulled the CTS plug and made sure it was making good contact with the CTS, and I haven't gotten the code since. CTS, MAT, and TPS all share a ground though so it makes me suspicious of the wiring... The code 15 was AFTER I fixed the TPS connection.

I also got code 32, that was when I figured out that the EGR valve and solenoid were both toast. That was quite some time ago and I haven't had any problem with the EGR system since then.

ede

did you set your timing with the est unplugged? is your know senser working correctly? you said you get knock with 92 octane, did you determine this from looking at the senser with a scanner? might try to by pass it or try a new one unless you're sure it's good.

Eggplant Jeff

I set timing with the brown wire disconnected. I also set minimum idle speed according to my Chilton's directions.

I already replaced the knock sensor. I hear the knock with my ears, which makes me wonder why the heck the computer is not retarding to compensate. That's why I replaced the sensor. I am NOT sure that it is good, except that it is new so it's probably good. But I've gotten bad stuff from autozone before. However I still shouldn't be getting knock the way my car's set up... Stock compression, 93 octane, 2 degrees advanced.

Vader

EJ,

Maybe I missed it somewhere in your text, but what year/engine do you have?

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Later,
Vader
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fb305svs

Vader, sounds like an L03.. dunno the year, didnt see a year listed...

well, its apparant that for some reason, you have one of these two possible problems. you are not getting the proper amount of fuel, OR, for some reason, ur timing is TOO far advanced. Now, y you would have any of these problem i do not know, but i think i would start with timing, seems how your idle is kinda wierd. the thing that makes me feel there mught be a possible lean condition is the fact that it bogs, bogs worse in cold air (which needs more fuel) and idles funny. Another reason that points me to fuel is the fact that you have knoocking. have you tried retarding the timing? does it still do it? mayeb try that. other wise, what are your O2 reading number when in full closed loop. if you provide us with number for the 02, we could tell you if it is running lean or not. maybe the best thing here would be to get it hooked up to a scan tool.

final conclusion, i think there is something in your fuel system, that is preventing the proper amount of fuel from reaching the cylinders....

Steve

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Eggplant Jeff

Vader, it's a 92 L03.

fb305svs, I would think a fuel problem would be more evident at higher RPMs rather than lower, whereas my problem is more evident at lower RPMs and idle than at cruising speeds (2000+ RPM... not evident at all in fact). I haven't gotten an O2 reading in closed loop lately, but last time I did have it on a scanner the O2 output looked normal. At idle it varied above and below .500 like it's supposed to... unfortunately it was Diacom on a desktop PC so I couldn't test-drive it under the scanner.

I retarded the timing from 7 degrees advanced to 2, didn't make a real noticable difference in knocking. I can try retarding it more if you'd like... The odd thing is that the knocking seems less pronounced in closed loop than in open... which still makes me go back to my idea that it's a vacuum leak. The computer could be partially compensating in closed loop by watching the O2 sensor, seeing lean, and enriching the mixture.

The knocking did start with a tank of 87 octane (I'd been running 87 for months) at a hole-in-the-wall gas station... So maybe I should try changing the fuel filter again and running a bottle of fuel system cleaner. But that was 4 tanks of Texaco 93 ago, I would think any bad gas related problems would have worked themselves out by now. Maybe the problem is it was ONLY 4 tanks ago... I haven't gotten that "5th tank feeling" yet . It's possible the knocking is a second problem, unrelated to the idle/bogging.

Oh yeah, I don't remember if I said it above or not, but the knocking is only evident at low RPM part throttle acceleration. I.E. if I floor it off a stop sign, no knocking. If I gently pull away, it'll knock a little.

[This message has been edited by Eggplant Jeff (edited September 18, 2000).]

AZDave

Jeff,
The stumble, hard start, especially when cold points to a lean condition.
The fact that you get no better driveability when using increased fuel pressure, points to a fuel delivery probblem.
My TBI responds immediately to even small variations in fuel pressure.
Unrelataed, but an idea to increase performance - gap your plugs wider. With the ignition you are running, you should benefit from a .045-.050 plug gap.

Eggplant Jeff

AZDave, I was running Bosch Platinum's gapped at .050, but I think they were rated too cold. At any rate I decided to go with the stock gap for now until I can lick this problem for good. After that I'll do the little things like larger plug gaps.

OK I'll change my fuel filter next, and run a bottle of fuel system cleaner. I still can't believe that a fuel problem would be only evident at low RPMs... But I'm willing to try anything. Anything else fuel-related I should check/change?

fb305svs

hmm jeff.... this is a very confusing problem. because tere are conflicting problems. one might be related to the other, then they mgiht not be...

i would try purging the fuel system agin with a bottle or two of the cleaner and a new filter. i guess give it a try and get back to us.

Steve

Red Devil

Hey Jeff, just out of curiosity, how did you check the injector spray patterns? It really does seem fuel related, I'd take a look at those injectors again and make sure they don't just dribble in light duty cycle.

Eggplant Jeff

Red Devil, on a TBI it's really really really easy to check injector spray pattern. Remove the air cleaner :-).

The two injectors are mounted above a two-barrel throttle body, picture a 2bbl carb with injectors mounted above the middle of each bore. So when the air cleaner is removed, you can see the fuel spraying out of the injectors. And it is very definitely spraying in a nice fan, no noticable gaps (like a shower head) just a nice even spray all the way around on both injectors. Definitely not dribbling.

Also it doesn't leak when you turn the key to ON but don't start the engine. It is also very easy to tell that when the injectors are right out where you can look at them. :-).

OK guys here's another datum. When the engine is idling, and it's got that faint stumble every few seconds, usually oil pressure jumps a little just as it stumbles. I've been assuming it was just reflecting the fact that the engine isn't turning over smoothly and correspondingly not turning the oil pump smoothly, but I'll throw it out there for you guys to consider.

Vader

EJ,

I had a similar problem on a TBI V-6. That episode has taught me never to use anything but an AC PCV valve. Check the manifold vacuum at idle. Pull the PCV feom the rocker cover and cap the end of the valve with your thumb. If you see a significant change in idle vacuum, you might want to pop a few bucks for a new PCV. Inspect the hoses while you're at it. Once you get a good PCV installed, you will likely have to reset the minimum air position. If you have been running for a year on your replacement IAC, you might want to clean the air passages and IAC pintle. As long as it is unplugged to set the minimum air postion, you might as well remove the IAC and clean it and the passages thoroughly.

Failing that, you might want to check the actual output of the MAP sensor with a scanner instead of a DMM.

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Later,
Vader
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"Make Me Bad"
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Eggplant Jeff

Well my PCV valve is new (<1 year) and from a GM dealer so it should be correct. It rattles like it's supposed to but I'll try capping it with my thumb. I doubt it's the problem though because even with the vacuum line to it plugged, my car bogged on start.

I'll try cleaning the IAC but I am doubtful that will help.

Red Devil

Hoo boy, missed that, I'm either going to have to drink more coffee, or get to bed on time and visit during the day!! Ouch!

Anyway, I didn't see a mention of the ignition module. Have you had that tested? Also, which dist. do you have? Is it the coil in cap? Double check the ground metal tab (matel goes from middle to corner under coil) for excessive corrosion or oxidation. Also check the carbon brsh while your in there. The more I look at the fact that it gets worse as it gets colder (yet another thing I missed) leads me to now believe (I sound like Clinton!) it could be an electrical problem. Sorry for the rush, but it past midnight and I need some bed! Good luck!!

Eggplant Jeff

I had my ignition module tested, came out clean.

I've got the remote-mounted coil, it is a new MSD GM Blaster (stock replacement). It is of course in great condition. I'm not sure what carbon brush or ground tab you're talking about, I assume they're only on the coil-in-cap distributor.

Eggplant Jeff

OK One more thing, I pulled plugs 1-5 because I can do it in half an hour without jacking up the car. 1 and 2 looked great, 3 and 4 had some slight carbon deposits on the rim (from the burn pattern it looked like they were somewhat shrouded by the side electrode), but 5 was interesting. It was similar to 3 and 4 (slight carbon deposits on the rim) but it also had a lot of carbon between the threads and the hex-shaped part. I.E. the carbon was working its way past the threads.

Any idea what this might mean?

I put the plugs back in tightly and started it, same bogging as normal. I wish I had time to jack the car up and pull the other three plugs and see how they look...