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Discussion Starter #1
Doing a little trouble shooting with this 1991 Caprice I just acquired. It's a 305 TBI car and otherwise run of the mill.

Problem it has, is that anything beyond 25% throttle it falls flat on its face. It's particularly bad before it's had time to warm up. Once it warms up the condition is still present but you can at least hammer the throttle and it'll get with it slightly better.

So, basically what were looking at is, any pedal input between 25% and 100% throttle causes the car to cut out badly. Car surges at idle at random once it's warmed up, otherwise smooth. Car hardly idles when the motor is cold. Car revs fine in park or neutral, no load on it.

I checked for broken vacuum lines, vacuum leaks at the TB base. Nothing there.
Pulled codes from it and they were:

33 Map - high voltage signal
34 Map- low voltage signal
44 O2- lean
22 TPS - low signal voltage
23 Manifold air temp

SO, I replaced the Map sensor and TPS with brand new ones, cleared the codes and SHAZZAM! Still runs like turd. :dunno:

Nothing has changed, and now it doesn't have any codes stored that I've been able to retrieve. Drove it around for 5 minutes and let sit in the driveway for 15 mins at idle and still no codes set.
I thought for certain the sensors would have at the very least improved the condition even somewhat.


Anyone seen this before on one of these cars?
I'm wondering if it's a weak fuel pump. The injectors appear to be spraying as they should at idle, of course that doesn't mean they are while it's under a load in gear and I'm not quite talented enough to watch them while driving it. :giggle:

Looking forward to everyone's input on this. More looking forward to being able to drive the car with it running correctly, it's a good riding cruiser. It does however need to be cleaned inside very badly as the inside smells like fat sweaty old guy and the interior has an inch of dust and funk through out.
:WTF:


Thanks in advance guys!
 

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SOunds like the same problem as mine... accept mine doesnt fall on its face at throttle.
When you replaced the TPS did you adjust the voltage? Is there even adjustment on your TPS? Check the voltage coming off the TPS pigtail at idle using a voltmeter.

Also, you may need to change your o2 sensor... a bad o2 can also cause idle issues.
 

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Discussion Starter #3
It's nonadjustable. I have figured out that the gas gauge is not working correctly also, it's stuck on full. Could there be a correlation?
 

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Doubtful, are you losing any fluids? I wonder if you have a bad intake leak.
 

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Discussion Starter #5
Leaks some oil and is an altogether grease ball, but no major amounts from the intake.
It did finally throw codes again today. I got 22, 23, and 44. TPS low volt, manifold air temp and O2 lean, again. I checked voltage and most of the sensors while running, and checked grounds. Seeing 5.02 at the sensors and cleaning the grounds up made no changes. Other thing I noticed today is that the exhaust smells horrid. Car revs fine with no load on it, but as soon as I put it in gear and power brake it, it starts stumbling and falling on its face. Could weak fuel pressure cause the computer to throw these codes? I can't imagine, but it is OBD1 we're dealing with here.
 

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The exhaust smell is probablly linked to the o2 sensor. Worth replacing. The high idle issue sounds like its related to the TPS voltage being off. When you replaced, did you do a ECM Idle relearn process? I believe thats recommended whenever changing the TPS.

Also, 5.02V at the TPS? That doesnt seem right... I thought the max range on those was 5V, at full throttle?
 

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Discussion Starter #7
The exhaust smell is probablly linked to the o2 sensor. Worth replacing. The high idle issue sounds like its related to the TPS voltage being off. When you replaced, did you do a ECM Idle relearn process? I believe thats recommended whenever changing the TPS.

Also, 5.02V at the TPS? That doesnt seem right... I thought the max range on those was 5V, at full throttle?
Not familiar with the relearn process. I wasn't measuring the tps itself, rather the wires that connect to it from the harness.
 

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Is it a 3 wire connector? Measuring voltage at the pigtail would be a viable way of doing it, if done correctly... you would need to know which wire is which.

Not sure on the relearn for your car either, but on mine it is just unplugging the battery for 15-20 minutes, then turn key to on position for 30 seconds, then off, then start the car up.
 

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5v is correct for signal voltage, output should be about 0.6 closed.
 

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Discussion Starter #10
Hooked up the scan tool today. All sensors seem to be reading as they should, the o2 was working semi well in the driveway but it was setting code 44 o2 lean again. Wouldn't repeat any of the codes again even after taking it out and driving the shit out of it. Car runs horrible in closed loop, then in open loop it's still bad but it'll at least move under it's own power. At one point in open loop the o2 was seeing zero volts. When working correctly it seemed to sweep as it should. But, still the computer's setting code 44 even after clearing the codes 3x. When we first got the scan tool hooked up at the beginning, it had an EST code set. Couldn't ever get it to duplicate it again. You can audibly hear that it's dropping cylinders, and backfiring through the tail pipe. Checked the timing, chain is a little loose but well within acceptable parameters.

I'm about lost with this one. :lol:
 

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Reading back through the thread, you never mentioned checking the plugs, wires, cap, and rotor.
 

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They all look fine, nothing's melted. I need to swap computers to see if that's a problem. Can't find one locally for the life of me though. I don't have any fittings that'll work with this cars fuel system to check fuel pressure. Anyone have a link to the right one, or a trick to doing it?
 

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Discussion Starter #13
Well, managed to stump the entire forum. My luck as usual. :lol:
 
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any fixes?

Hey I'm pulling the same codes (22,23,32,44) same issue dying when throttle any fixes?
 
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