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Discussion Starter #1
Hi gang! I'm new to the board and this thread may have been beaten to death already but here goes.

I have a 92 Burb that recently developed a miss under load. Truck starts fine, rev's up fine in park, but once you put it in gear it falls flat on its face! I replaced the MAP sensor, IAC, EGR, EGR solenoid, wires, plugs, cap, rotor (good stuff, AC Delco and cap with brass fittings). I did the cap and rotor a few months ago and the truck had been running fine.

The trouble started a few weeks ago. Ran great going down the highway and when I came off the off-ramp to a stop sign it seemed to want to die. Came to a stop fine, but when I went to take off, it loaded up and started missing. Mashed the go pedal and it took off. After that didn't have a problem. Few more days go by and no problems. It was intermittent like that for a few weeks. Now it does it all the time. Starts fine, idles fine, you can rev it up, (although it seems to want to load up a bit when you jam on the gas), but when you put it in drive and hit the gas, she just stumbles baaaaad!

I am going to try and put in a new coil, could be weak and for only 20 bucks it's worth a shot. I have looked for arcing..nada..I tested resistance on all the plug wires..every one is within spec (less than 1000 ohms per foot).

This is driving me nuts! HELP!!
 

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Have you looked at the fuel system (pump, filter, relay, etc.)? If the fuel pressure/volume is low, you will get those symptoms. Just something to think about.
 

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Discussion Starter #3
Yeah, thought about that. The stream of fuel thru the TBI appears to be sufficient. No interrupted fuel flow or sputtering as if the fuel filter was clogged. I probably should have mentioned that the fuel filter was replaced. Someone did mention a fuel pressure regulator as well. I could swap that out and see. Thanks!
 

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Discussion Starter #4
O.k., fuel pressure regulator is good to go. Still same symptom. Revs up just great in park, put it in gear and she falls down. Now, I can rest my foot on the gas and it will go alright, but if I try and accelerate, she just stumbles and pukes...ARGH!!!!



Yeah, thought about that. The stream of fuel thru the TBI appears to be sufficient. No interrupted fuel flow or sputtering as if the fuel filter was clogged. I probably should have mentioned that the fuel filter was replaced. Someone did mention a fuel pressure regulator as well. I could swap that out and see. Thanks!
 

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could it be that the tranny's on its way out and it's causing more than typical strain on the motor? If it's only doing it when it's in gear and you're trying to accelerate, it could be that the motor is ok idling, but when you throw it in gear there's something that's causing the crank to not run free, tranny pump going bad or something... This is pure speculation from what you've said and does not neccisarily have creedence in real life. ;)
 

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Discussion Starter #6
I thought that too, but it doesn't feel like a tranny going out. I know what that feels like. Plus, the tranny was rebuilt and only has 30K on it. It was an intermittent problem, but is now more pronounced. Check my first post. It's really weird. Someone said it might be the distributer. It is the stock one and the motor has 210K on it. This one is weird though, it has a collar around the reluctor on the shaft. It is loose and wiggles back and forth a little bit, but not enought that I would think it would cause a problem, or at least, it should cause a problem all the time, not just under a load. Usually, the reluctor can crack and then that can cause this same symptom.. it's weird. Driving me crazy.


could it be that the tranny's on its way out and it's causing more than typical strain on the motor? If it's only doing it when it's in gear and you're trying to accelerate, it could be that the motor is ok idling, but when you throw it in gear there's something that's causing the crank to not run free, tranny pump going bad or something... This is pure speculation from what you've said and does not neccisarily have creedence in real life. ;)
 

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Discussion Starter #7
No other ideas?!?!?



I thought that too, but it doesn't feel like a tranny going out. I know what that feels like. Plus, the tranny was rebuilt and only has 30K on it. It was an intermittent problem, but is now more pronounced. Check my first post. It's really weird. Someone said it might be the distributer. It is the stock one and the motor has 210K on it. This one is weird though, it has a collar around the reluctor on the shaft. It is loose and wiggles back and forth a little bit, but not enought that I would think it would cause a problem, or at least, it should cause a problem all the time, not just under a load. Usually, the reluctor can crack and then that can cause this same symptom.. it's weird. Driving me crazy.
 

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I'd check for a vacuum leak. Also there is no substitute for an accurate fuel pressure reading.
 

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Could have a bad valve, valve spring. Also could be collapsed or stuck lifter. Which Cyl. is misfiring? once you find out take a compression reading. Make sure to cut fuel to cylinders, take multiple readings and see if the compression fluctuates from hi to low and vice versa. I had the same problem on a blazer not to long ago and it ended up being a valve spring. Also check for cyl. wash out. Good luck
 

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wouldn't a valve make a noise?
I'm stabbing here, my old computor car ran a little better after I found the O2 wasn't adjusting right. I didn't see o2 on your list.There is a test you can do on o2 while on the pipe.
 

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I thought that too, but it doesn't feel like a tranny going out. I know what that feels like. Plus, the tranny was rebuilt and only has 30K on it. It was an intermittent problem, but is now more pronounced. Check my first post. It's really weird. Someone said it might be the distributer. It is the stock one and the motor has 210K on it. This one is weird though, it has a collar around the reluctor on the shaft. It is loose and wiggles back and forth a little bit, but not enought that I would think it would cause a problem, or at least, it should cause a problem all the time, not just under a load. Usually, the reluctor can crack and then that can cause this same symptom.. it's weird. Driving me crazy.
strange,, the timing, when under sudden load, needs to retard. so as not to ping.
Did you ever hear a ping before or after it misses?
Is there a way to tempurarily, jam the collar so it won't wiggle and stay firm? then test?
(couch mechanic)
 

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Discussion Starter #12
True. This problem started gradually. Would happen and then it wouldn't for days.. and it wasn't as pronounced as it is now. But now it does it all the time. Whats really tweaking my melon is that in park, it revs up just fine, but as soon as you put it in gear and try and go.. it just stumbles and loads up. If it were a bad valve spring the valve would be making noise and I would basically have a dead cylinder. Compression tests are all good. If I had a burnt valve or "washed out" cylinder it wouldn't rev and run in park like it does. I'm beyond part swapping at this point..might as well put a whole dang engine in the stinkin thing. LOL! Anyway, the fuel filter is relatively new (date written on it, was replaced about 4 months ago). I am going to replace the fuel filter tomorrow anyway and do another fuel pressure test. AUGH!!! :grrrrrr:


wouldn't a valve make a noise?
I'm stabbing here, my old computor car ran a little better after I found the O2 wasn't adjusting right. I didn't see o2 on your list.There is a test you can do on o2 while on the pipe.
 

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Discussion Starter #13
O.k. Swapped fuel filter. No joy. Checked fuel pressure again, still good. Even took apart the fuel pressure regulator.. all is good. I'm still thinking it is electrical. Now, I know I did a full tune up about a month and a half ago, but I checked the wires and found that the resistance was out of spec. By rule of thumb, you should have no more than 1000 ohms of resistance per foot of wire. I had a 3 foot wire that was registering 12,000 ohms of resistance!! Yipes!!! And these are supposed to be "premium" plug wires! Forget that. I knew I should have gone with old faithful to begin with, MSD. Swapped in the MSD's and checked all the plugs too. All the plugs are clean as a whistle.

So after exhausting myself half the day on this, I was cleaning up and decided to jump the A/B port on ALDL and see if the computer sees anything. Now, there is no check engine light on, but it flashed out an ignition module (42). I think thats about the only part I didn't replace at this point. Sooo, what the heck.. I'll go to the parts store tonight and get one and drop it in. If the ceramic is cracked I could see it behaving like it is...ahhh, anyway, I'll get one tonight and drop it in and let everyone know. Thanks everyone for the help!
 

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I'm sitting on Pins and N*&%$#. I'll be back, i got to go get some bandaids.
Later you can send us a pic of the vehical you fixed.
 

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Discussion Starter #15
AUGH!! O.k. Swapped wires, and put in a new ignition module. Now the problem seems worse!! RRRGGGGHHH!!! I fired it up, and it imediately died. Fired it up again and it sat there and loped for few minutes, then it finally settled down to idle. WTF?!?! Just tried to drive it thru the neighborhood and it could barely get out of the driveway!! She just spat and sputtered and it wouldn't hardly move. I wish I had an oscilliscope so I could see what the heck is going on! If it's a spark issue then I could figure it out. Maybe the pickup is shot on the distributor shaft. I don't know. Maybe the timing is not advancing like it should. But even if the timing didn't advance, it would still go, just not with any power...this thing just spits and sputters and coughs and will not go anywhere!! Part of the definition of the code 42 eluded to possible PCM failure? Do I bite the bullet and buy a new PCM?!?! I have the GM factory manual to do testing of the boards in the PCM. Maybe I'll do that and see what the heck is going on. AUGH!!! A new Burb is looking reeaalll good right about now!!
 

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Your keyboard must be pretty dirty..
Can you back up, undo what you did? We see that is not the problem. Or double check your installing. Things should not get worse. Got any local mechanic friends?. Something is being missed, . your in the right fireing order? Many of us have done that. O.K.,,, just me , many times though.:gasp:
 

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Oh, I'll admit, I've done the wrong firing order before, and got to watch the exhaust manifolds turn cherry red. LOL I've gone thru and double checked everything. I do have a friend that owns a shop here in town and I've picked his brain about it too. everything he has suggested I have done or tested out. Basically at this point, I have not replaced the TPS, the pickup and the PCM. What next?
 

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Have you checked the distributor gear? If they start to wear, it can throw the timing off or even jump a tooth. Just a thought.
 

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I have to say that you are a very patient individual.

If it were a horse, I would've shot it back when you changed the map sensor. :lol:
 
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