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92 PA miss when cold under 1500 RPM


onetoomanyoldcars
06-15-2008, 12:24 PM
I have a 1992 Buick Park Avenue, non-Ultra, non-turbocharged with 185,000 miles that I bought on Ebay in December of 2007 that I am having a problem with. This is just the latest of many problems I have had with the car since I purchased it. The car has a miss, or at least that is what I think it is, when you start it cold first thing in the morning or after letting it sit all day at work. The car pops and spits through the tailpipe and shakes badly, you can feel it through the whole car. This lasts only for about 10 minutes until the car warms up. The miss seems to go away immediately though if you step on the pedal and bring the idle up to above 1500 RPM and then comes right back if you allow it to go below 1500 RPM again.
The car seemed to start doing this right after I replaced the crank and cam sensors. I replaced them because the car was dying about every time I drove it and it had an error code 17 in the computer. Since replacing the two sensors over a month ago, it hasn't died once and it does not get any error codes any more but now I have this new problem.
I took it into a local shop and had the owner and head mechanic who has over 20 years experience try to find out what is wrong. He checked the plugs, plug wires, coils, ignition/spark module, fuel injectors, compression, etc. and his best guess is that I either put in a defective crank sensor (I put in an Auto Zone one, not a genuine GM one) or that I didn't get it aligned properly (I used two non-magnetic feeler gauges, not the $500 GM J-37089 special dealer tool.) In a way this makes sense, but on the other hand, why would this cause it to miss only when it is cold?
I should also mention that I am getting only 16 MPG now in the summer and was getting only 13 MPG in the winter. This is mainly in-town driving, trips 5 miles or less, but I still think it should be better.
I also have tried a new ignition/spark module and a set of different (used) coils. Also, the guy at the shop replaced the #4 spark plug because his scope was showing a miss on the #4 cylinder when cold, but none of these things have helped at all.
Can someone please give me some advice on what is wrong or what I can try to do next? Thank you!

HotZ28
06-15-2008, 08:16 PM
I took it into a local shop and had the owner and head mechanic who has over 20 years experience try to find out what is wrong. He checked the plugs, plug wires, coils, ignition/spark module, fuel injectors, compression, etc. and his best guess is that I either put in a defective crank sensor (I put in an Auto Zone one, not a genuine GM one) or that I didn't get it aligned properly (I used two non-magnetic feeler gauges, not the $500 GM J-37089 special dealer tool.) In a way this makes sense, but on the other hand, why would this cause it to miss only when it is cold?
Welcome to Af! With all due respect to your mechanic with only 20-yrs experience, I think his “best guess is that the crank sensor is defective, or installed wrong” does not make sense! :shakehead The CKPS will not cause the car to pop and spit through the tailpipe and shake badly, only until it warms up! Your proof of that is in your quote below.
Since replacing the two sensors over a month ago, it hasn't died once and it does not get any error codes any more but now I have this new problem. Do not assume that the new cam sensor is not defective, or that it somehow made contact with the interrupter magnet on the cam sprocket. The cam sensor controls fuel injector timing and can cause sputtering and hesitation. The timing must be correct for the injector to fire when the intake valve is opening. Check for any scratch marks on the cam sensor. In addition, check the cam interrupter magnet and be sure it in place and not damaged.

If all this checks good, you may want to check the CTS sensor with a scanner while the engine is cold. The CTS sensor tells the ECM what the operating temperature of the engine is. When the engine is cold, it needs more fuel to operate properly and if it is cold enough, it will inject a large quantity of fuel to start the car. This is called Cold Start Enrichment and replaces the function of a choke.

The ECM sends a 5-volt reference signal to the CTS sensor. As temperature changes in the coolant, the electrical resistance of the CTS sensor also changes. The best way to test this sensor is with a scanner. When the engine is cold, engine coolant temperature should measure near the same as the ambient temp. Another way to test the CTS sensor is to measure voltage from the time the engine is started, until it warms up. Record the voltage changes as the engine warms up to operating temp. i.e. 120, 140, 160 & 180. You should see close to the full range of voltage (5.0-1.0V) during this test. If it does not change from what you first measured cold, replace the sensor! And finally, if you prefer you can check resistance of the sensor using the chart below;
http://img293.imageshack.us/img293/7281/ctsmatdd8.gif

onetoomanyoldcars
06-17-2008, 06:26 PM
Thanks for the reply. I have not had a chance to check the cam sensor or cam magnet yet because it is a real pain to get at them due to where they are located. I did get a chance though to check the Coolant Temperature Sensor and it seems to be working fine. I don't have a scanner to check it, I wish I did, but I do have a multimeter so I checked the resistance of the CTS through its full range of temps and it seems to be good. I got 3500 Ohms when cold in the morning (It was about 60 to 65 degrees outside) and 220 Ohms when fully warmed up. I also looked at the Ohm readings many times as the car warmed up and they all seemed normal.

I was reading in my 92 Buick shop manual again and in the section about misses it does suggest the possibility of the crank sensor not being aligned properly or the possibility of a bent vane on the harmonic balancer. I think I will have to check this out again when I get a chance to pull it apart again. I wish I could find someone who would rent me or loan me that special J-37089 crankshaft sensor alignment tool! I still don't understand why the car would only seem to miss when it is cold and under 1500 RPM though.
Any more new ideas of other things I could check? Like I said, I don't have a scanner or much at all for fancy tools and I do all my work outside, I don't have a garage. I only have simple tools like a multimeter and I do have an old oscilloscope that I just bought last week at a garage sale for $5, but I don't know if it will be of any use, I really don't know anything about it. I also don't have much money to spend. I have already spent about $500 trying to fix this car on top of the $1200 I paid for it! This is the newest car I have ever owned and it is my daily driver for work and everything else! Thank you!

onetoomanyoldcars
06-17-2008, 06:39 PM
I just thought I should mention, because I forgot to in my original post, that I also did replace the oxygen sensor and did check the air filter (It looked almost like new.) I also pulled all of the plugs and checked them myself, even though the mechanic did this also, and checked that all of the gaps were at the proper .060 and that they looked normal.

One more thing. I was just curious if you think that my 13 MPG winter in town and 16 MPG summer in town mileage is below normal for this car.

A final note. I am STILL not getting any error/diagnostic codes from the car's computer.

Thanks!

onetoomanyoldcars
06-23-2008, 08:58 PM
Great news! I solved the problem! It turns out it WAS the crank sensor. It WAS slightly out of adjustment.

I took off the harmonic balancer again to check it and I could see areas on the interrupter rings where they had been very slightly rubbing on the crank sensor. The one ring had marks on its inside edge for about one third of its travel and the other ring had marks on its inside edge for about two thirds of its travel. The marks were VERY noticeable. They more or less just looked like the metal had been polished, it was brighter and cleaner than the other areas that had not been rubbing. Fortunately the rubbing was not severe enough so that the crank sensor had been damaged.

I reset the gaps using a special set of non-magnetic feeler gauges that were made specifically for GM crank sensor alignment. I found a company that used to make these which is located only about 70 miles from me. They told me that they don't make them any more but had about 40 sets left in stock. I paid only $4.64 plus $1.50 shipping and handling for them! I could give the name, address, and phone number of the company, but I don't think I am allowed to on this forum. I remember seeing that selling is not allowed on here. I of course do not work for this company and am not trying to sell anything, but I would love to pass on this info if it could help out some other people. It sure beats paying $500 for the J-37089 alignment tool!

Anyway, I reset the gaps and now the car runs great all the time, even when it is totally cold. No more misfiring!

I also began thinking about why the interrupter rings were rubbing only in certain areas and not consistantly all the way around and came up with one theory, but I am not certain that this is the reason. I noticed that when I screwed the three bolts for the puller into the harmonic balancer, two of them had another non-threaded hole to go into after they got beyond the threaded part of the hole, but one did not. The one that did not have the extra non-threaded hole to go into would hit a dead-end against the piece of metal that the interrupter rings are a part of. Possibly if this bolt was tighted down against this dead-end it could maybe slightly bend this piece of metal with the interrupter rings on it. I am not sure, but it might be possible. To avoid this a person could use an extra washer on this one bolt or just use a slightly shorter bolt.

Anyway, if this is why the rubbing was not consistant all the way around the interrupter rings, I do not know, but I do know that at least the inconsistancy was small enough that I was able to allow for it and get the gaps adjusted well enough so that the car does not misfire when cold anymore.

I am now wondering if I should disconnect and reconnect the battery so that the computer can reset itself and start to learn from scratch again since I reset the crank sensor gaps?

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