1993 LeSabre Idle Rough after Code 18 After Repairs - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-22-2011, 03:10 PM   #1
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Default 1993 LeSabre Idle Rough after Code 18 After Repairs

In the summer my '93 LeSabre started cutting off hot. Would crank cold. No trouble codes were set. I used Just Answers to try and get help. The problem with the car was finally resolved by replacing the MAF sensor; which I discovered was bad. The Just Answer guy simply told me to replace one component after another. I was told to replace the ICU, the cam sensor, and the crank sensor until I finally inspected the MAF and found the heated wire was gone. To recap, I have replaced the coolant sensor, the Ignition module, the cam sensor and the crank sensor. After replacing the MAF the car ran great. No problems until around two weeks ago when I started the car in the morning to allow it to warm up and warm up the interior since it a very cold morning; about fifteen minutes idling. When I went to leave the car was running a bit rough and when I got inside noticed the check engine light was on. I turned the engine off and then restarted it. The check engine light was off then came back on. I decided to not drive the car. I check the trouble code and it flashed code 18. A search of the net said that was a cam/crank error. I checked the connectors and they were tight and I could see no breaks in the wiring where they enter the connector. I removed the cam sensor and checked that the magnet was in place and it is. I checked the wires from the cam sensor to the ICM and they checked OK by ohmmeter. Checked the wires from the crank sensor to the ICM and they checked ok. I decided to put the old ICM back on the car and same thing, code 18. Put the new ICM back in place and decided to order GM service manuals both mechanical and electrical off of ebay (great buy, got the set for $20.00 with shipping).

When I got the service manuals I followed the steps for code 18 check. Took the PCM out and disconnected the connectors. Checked for the 5 volts at the connector and it was there. Rotated crank until magnet was over cam sensor and voltage went to zero. So cam sensor ckt and magnet are working. Checked for the 5 volts at the fuel circuit per service manual and the 5 volts was there. OK, at this point all the wires check out and the 5 volt signals are there. Plug the computer back in and started the car. No code 18 but the car idle rough sometimes idling down and back up. Maybe the computer recalibrating? Car finally smoothed out somewhat, no surging or anything but still a rough idle. No code 18 gets set. Perhaps the connector was just loose at the computer. Still, the car is not idling as it should. Borrowed a scan tool and took a data stream capture.

Not sure which readings will help so will post what I think may be of significance since I can not get the Cornwell 2499 tool to connect to my computer.

LT Fuel Trim: 128
LT Fuel TR CL: 5
Evap Solenoid: off
EGR Sol all of them off
KS Counter: 1
Exhaust O2: Lean
IAC Position: 140
Idle Req RPM: 1288
ST Fuel Trim: 128
Knock RET: 0
Loop Status: OPEN
MAF (sr/*): 3708
IAT (degrees F): 53
O2S (mV): 466
O2S CROSSCNTS: 54
PROM ID: 1284
QUAD DRIVER 1: OK
QUAD DRIVER 2: OK
Spark Adv: (degrees): 23

I checked the coil packs and the secondary terminals read ~10K ohms on my cheap ohmmeter.

The engine has over 300K miles on it. I am the third owner. The first owner kept proper maintenance. However, at this time I have no real idea if the timing chain/gears have been replaced. Is it possible the chain jumped a tooth or two and caused this problem? Is it possible that the 18x on the crank sensor is bad? When I replaced the crank sensor, I checked the vanes and they were all there and none of them bent. The plastic guard was put back in place when I reinstalled the pulley. I don't see how a vane could get bent or missing just sitting and idling in the drive. I understand that the 3x would keep it from starting if it was bad. I had no way to really test the output of the crank sensor since the ICM connector has to be in place. One place said to use a wire piercing tool which I don't have. The Code 18 never came back, but I can tell by the way the engine shakes a bit that it is not idling as it should, I have had this car a while and I know how the engine should sound at idle. This is my only car at this time so I need to get it running again.

Thanks to all in advance .
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Old 11-22-2011, 03:16 PM   #2
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Opps, the scan tool used is a Cornwell 3499
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Old 11-22-2011, 05:13 PM   #3
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I have now found out that the timing chain and gears have not been replaced in this engine. It has 323,215 miles on the engine. Is it possible the timing chain jumped a couple of teeth after it started and that threw the Code 18?
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Old 11-23-2011, 12:45 PM   #4
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I was reading on another forum that the engine will stay in open loop until the O2 sensor is warmed up. How long does that take? How many minutes should I let the engine run before I do a data stream capture? I am afraid of running the engine too long as I don't know what is wrong and I don't want to do any damage. I am going to change out the timing gears and chain but I want to know about the code 18; maybe just loose connector but the engine is not running correctly. I need to take the scan tool back soon.
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Old 11-23-2011, 12:54 PM   #5
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its not likely chains strech when they wear, not skip. you can take a look at the gears they should have dots that line up.

as far as your engine running poor it looks like the scan was at start up. what does it do if you drive it for a while until it goes into closed loop?
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Old 11-24-2011, 12:56 PM   #6
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I can not drive the car but did let it run until the engine was hot. The engine started running very rough, almost cutting off and the Code 18 returned. I did manage to do a data capture.

LT Fuel Trim: 135
LT Fuel TR CL: 5
Evap Solenoid: off
Coolant Temp (F): 114
EGR Sol all of them off
KS Counter: 13
Exhaust O2: Rich
IAC Position: 103
Idle Req RPM: 1050
ST Fuel Trim: 128
Knock RET: 0
Loop Status: OPEN
MAF (sr/*): 2791
IAT (degrees F): 52
O2S (mV): 955
O2S CROSSCNTS: 54
PROM ID: 1284
QUAD DRIVER 1: OK
QUAD DRIVER 2: OK
Spark Adv: (degrees): 7

Does this help? I am wondering if the return to Code 18 is a problem with the crank sensor? The service manual said that if all the other tests did check out, inspect the crank sensor. It is new, but could be bad.
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Old 11-24-2011, 02:55 PM   #7
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The engine temp is still cold on that capture.

With 350+ thousand miles, I would bet that it could stand to have a timing chain job. I believe the service interval on those is 100k miles, but no one ever does it. If the chain has stretched enough, and for what ever reason the tension is not what it should be anymore, I could see where it maybe jumped timing. They way to find out though usually is to pull the timing cover off, which with those miles, you may as well replace the timing set anyway.

As far as crank sensor being bad? I haven't heard of one failing like this, but I do learn something new every day.
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Old 11-25-2011, 01:43 PM   #8
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The engine was starting to die on me when I made the capture, so that was as long as I could let it warm up. However, I believe that it should have been in closed loop at that temperature.

It is the Code 18 return that I want to resolve. Would jumping a tooth or two on the timing gear cause Code 18 to appear? If not, then I want to address the Code 18 before doing anything else. I went down through the list in the GM service manual. At the end it said that if all the tests for Code 18 checked out; which they did, it said to check

Poor connections at PCM: None found. Took the cover off and checked from pin to solder joint on the board and checked good.

Harmonic Balancer Interrupter Ring Vanes Bent or Missing: When I replaced the crank sensor, I checked the vanes and all were as they should be. Question, could something have happen to them from cranking it to warm and throwing the code 18?

Faulty Crank Sensor: Well, it is a new one but I suppose ti could have went bad and not sending the pulses each time it should. I could check for this with an oscilloscope but I don't own one and can not afford one. I don't have a wire piercing probe, but I guess I could "make" one and then turn the crank by hand looking to see the voltage spikes as the vanes move through the sensor.

The last says to check the circuits 630, 633, 644 or 645 (diagram only shows a 645). It also states a faulty cam sensor could cause the PCM to reinitialise causing a stumble or miss. However, the cam sensor checks out, when the magnet was over the sensor, I read zero volts; off I read 5 volts. Also a fault in the fuel circuit; however, I checked that and I had 5 volts at the connector to the PCM. The last said to check the circuits for the crank sensor which I did. The book states that a bent or missing vane in the 18X part of the crank sensor, or a fault in the 18X part of the crank sensor circuit (which could be internal to the crank sensor) would cause the PCM to stop pulsing the injectors when the fault occurs. HEY, could that be why it went from running lean to rich?

So, should I go ahead and start pulling stuff off and change out the crank sensor? Removing the crank pulley is part of the job replacing the timing chain.
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Old 11-26-2011, 05:24 PM   #9
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chains stretch they dont skip so it seems unlikely thats your problem. however if i checked all you did i think my next move would be to start pulling the crank pulley apart and see if the pulse ring is messed up or if there is a shear key maybe if got bent. or maybe the chain is stretched enough the timing is off, there should be dots that line up.

what did you mean by cranking it to warm?
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Old 11-26-2011, 10:42 PM   #10
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I think the code 18 is from the crank sensor/pulley vanes because there isn't anything left.

Before this code 18 and after the repairs mentioned at the beginning the engine was running great; better than it had in a while since the MAF probably had been malfunctioning for some time. The code 18 started one cold morning when I started (crank; you have to excuse my terms; I know that crank is turning the engine over, not necessarily starting) the car to allow it to warm up the interior before leaving work. The engine started without problems and was running smoothly when I returned to the house. Upon returning to leave to go to work, I found the code light on and the engine running rough. I did no revving of the engine. when the weather is very cold, Dad told me to let it idle for a few minutes to allow the oil to circulate and the engine to warm before taking off down the highway.
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