97 lesabre "Stumbles"

[Smith1000]

Have a '97 Lesabre that has devoloped a stumble. When cruising about 30-40 mph, it will cut-out. When it does it, the tach jumps (drops w/loss of power and is erratic). It generally smooths out. Sometimes, it will not do this at all for a few days and then it returns. No codes on this problem so far. It is also experiencing poor fuel economy, about 21 mpg. It has done it occasionally when sitting, idling (in drive) w/foot on brake stopped. It will stumble just a bit. Occasionally, when pulling up and stopping, it will die. It will always restart though.

Could this be the crank pos. sensor or camshaft pos. sensor? The check engine light is not coming on for this. Any ideas? Thanks.

[maxwedge]

Originally Posted by Smith1000

Have a '97 Lesabre that has devoloped a stumble. When cruising about 30-40 mph, it will cut-out. When it does it, the tach jumps (drops w/loss of power and is erratic). It generally smooths out. Sometimes, it will not do this at all for a few days and then it returns. No codes on this problem so far. It is also experiencing poor fuel economy, about 21 mpg. It has done it occasionally when sitting, idling (in drive) w/foot on brake stopped. It will stumble just a bit. Occasionally, when pulling up and stopping, it will die. It will always restart though.

Could this be the crank pos. sensor or camshaft pos. sensor? The check engine light is not coming on for this. Any ideas? Thanks.

Tough diagnosis, check all the battery and engine grounds, the cam sensor will not cause this, a crank sensor could.

[LeSabre97mint]

Smith1000

What MPG were you getting with your 97 before this problem? I too only get 21 to 22 and can not figure out how to inprove it.

Regards

Dan

[Smith1000]

For years it would get 26 mpg, combined hwy and city driving, but my commute is 34 miles, so it was mostly hwy. Some city driving over lunch. Now, the same commute, it is getting about 21 mpg combined. It used to go about 205-210 miles when it was down to half a tank. It is now going abt 155-160 (trip odometer).

I thought possibly the crank sensor because it sends the signal to the ECM for rpms and crankshaft position and it seems to lose the rpm signal in the tach momentarily. I wonder if I can hook a digital voltmeter to the cranksensor to monitor the reading while driving? I would think there would be a code though, if there was a problem in the circuit. I will take a look at the grounds and see if they can be cleaned up.

[Smith1000]

I cleaned up all of the grounds, both sides on the fender wells. I also cleaned the battery ground. They looked fairly good to begin with though. I cleaned them up a few years ago. I'll drive it a few days and see if the problem still exists. I am focusing on the crankshaft pos sensor, based on what it is doing and what I have read. I have read that this car has had... "significant problems with the crankshaft position sensor, camshaft position sensor, fuel pressure regulator and idle air control valve."

I do not know if the crankshaft pos. sensor could ultimately create poor fuel economy. Probabaly could because I believe it has to do with timely fuel delivery. I can get a crankshaft position sensor for $25 which seems fairly reasonable.

[Smith1000]

It still has the problem, although it did not seem as severe today. The tach dropped and it powered out momentarily when going about 10 mph. It was cooler today. When I accelerated, it came right out of it. No codes; no check engine light. It is definitely a problem that only occurs when it is hot. I went ahead and picked up a crankshaft pos. sensor and will put it in Saturday.

[HotZ28]

The CPS can be “heat sensitive” and will cause the condition you are experiencing, however it has nothing to do with the fuel economy or timing of the fuel injectors. Injector timing is the work of the cam sensor. In addition, the ICM can also be “heat sensitive” and cause the “stumble” condition you described. I hope that the CPS will take care of it! Lack of fuel economy could be related to a bad 02 sensor, or timing chain stretch.
How many miles on the car?

[Bassasasin]

If the O2 sensor is bad it could be causing this problem.
When the engine shifts to closed loop (using the 02 sensor and others) it may not be a good mix..

You Could run without the O2 sensor connected forcing open loop condition. for a while, of course you would have to deal with the codes later realizing it was disconnected.

Open loop is used during start and RPM conditions. like speeding up to 30 mph and ten seconds later it goes into closed loop.
Closed loop is used when speed and sensors are warmed up and when they are actually used is determined by the PROM for your engine.

I think when the rpm goes below a certain RPM, say 1200 the system is in open loop.

The CRANKshaft sensor usually causes a violent stumble, but has been a popular, difficult troubleshoot sensor.

Good Luck..

[Smith1000]

Thanks. All helpful comments. I checked the codes again today just to see if there was anything. It is about to quit on me and I'll drive something else to get me through the rest of the week. Today it read code P1361. I looked it up and it indicates "Ignition coil control circuit-low voltage". Is this code familar to anyone? I have not found a lot of information about what this means, but I would say it is probably the Crankshat Pos. sensor. From what I have read, it is a "Hall-effect" sensor that acts as the pickup ignition controller and drives the current. Also, the CPS provides the tach reading which is dropping out. It is heat sensitive as it takes awhile for it to start the problem. I'll likely go ahead and replace the cam pos sensor too since it is located near the crank pos sensor. The car has 157,000 miles on it approximatley. If I am reading the scanner right, the code has set 4 times since Sunday. I replaced the O2 sensor about 20,000 miles ago. I would say this is problem is kind of a violent stumble...

[BNaylor]

P1361 is EST Short Circuit Fault or in other words Ignition Control (IC) circuit is not toggling. The ICM sends signals that the PCM requires for fuel control and spark advance calculations. At start of engine crank, the ICM controls spark advance in bypass mode. When the 3X signal is recognized by the PCM, it applies 5 volts to the bypass circuit commanding the ICM to switch to ignition control (IC) of spark advance to PCM (IC mode). To set P1361 there is either a short in the IC circuit or an open or short in the Bypass circuit.

Some of the possibilities mentioned above were the ICM module and crank position sensor. Other possibilities are the PCM module or the wiring harness/wiring between the ICM and the PCM.

The last SII 3800 that I worked on that had a Bypass/IC mode problem turned out to be a bad wiring harness between the ICM module to the PCM module. You'll need a wiring diagram to properly troubleshoot it.

[Smith1000]

Many thanks. I'll go ahead and replace the crank pos. sensor first. I can follow the wiring from the ICM Module to the PCM Module looking for damaged wiring or wiring harnesses. I basically understand the concept. I have a Haynes manual that has pretty good wiring diagrams. I guess it would make sense to start looking in the IC circuit first and then the bypass circuit.

[LeSabre97mint]

Hay Bayner

How much slack in the timing chain is too much? My 97, like I posted earlier, is only getting 23 at best MPG. I haven't checked the chain. What would one look at (no dis) to tell if there is slack when the crank is turned back and forth?

Regards

Dan

[BNaylor]

Originally Posted by LeSabre97mint

Hay Bayner

How much slack in the timing chain is too much? My 97, like I posted earlier, is only getting 23 at best MPG. I haven't checked the chain. What would one look at (no dis) to tell if there is slack when the crank is turned back and forth?

Regards

Dan

The cam gear and crank gear have timing marks so if the chain or any of the two gears is in bad shape you'll know. Basically it is just a general procedure applicable to all cars with a timing chain nothing special but to accurately verify it you have to dismantle the front end of the engine and pull the cover to check it. The chain is allowed some freeplay.

[Smith1000]

Just put in the a new crankshaft pos sensor and cam pos. sensor. The vibration damper/pulley was rather difficult to remove. The bolt was extremely tight and had to use a gear puller to slide the damper off.

The wiring coming out of the connector for the crank sensor was bare right on the end (no insulation)where the wires meet the connector. It looked like it had been bent and pulled up tightly (when installed) where it wound up to the top of the engine. The insulation was coming off and it looked like two of the bare wires were possibly touching eachother. All was caked with oil and dirt. I cleaned off the wiring well and separated them (all 4) and coated it with some liquid electrical tape. I am waiting for it to dry some and then I'll connect the wires and put the vibration damper back on. After that, I'll see how it does.

The crank pos sensor appeared kind of melted at first, but I believe it is just caked heavily with oil/dirt/etc. The vanes on the damper look just fine.

[Smith1000]

All is back together, but the problem is still present. Had to drive it for quite awhile before it stumbled and set code P1361. I am going to check the wiring around the ignition module, remove the harness, etc. The wiring diagrams indicate the bypass circuit wire and the other reference wires as treminals A,B,C,D on the module. I noticed the module and coils are extremely hot to the touch, but this is probably normal.