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93 Northstar running poor


Ed Hall

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Hi,

I've been having problems with my 93 Allante cutting out at lower RPM's and starting hard when warm. I haven't done anything yet but figured it was probably the FPR. Anyways, the problem has been getting worse and this morning after driving several miles, the engine starting running really rough and I lost a lot power. It feel like it is only firing on 5-6 cylinders. I get the code P081 (E081) - CAM to 4X reference correlation problem.

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Here's an update to the problem:

The problem started after not driving it for 6 months. It would hiccup while idling or under high throttles and low rpm's.

Today, the engine suddenly lost a bunch of power and it seems like several cylinders are no longer firing. This problem is occurring at all rpm's. I ran the on board diagnostics and monitored the MAP sensor and the TPS and did not see anything wrong. I also reset the codes and nothing came up. I'm thinking the problem could be either a coil pack or FPR. What do you think? What else should I check before randomly replacing expensive parts? I'm currently 200 miles from home and will have to drive the car 200 miles back this weekend. I hope I make it. :o

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If you haven't done so yet, clean the battery cables. Don't forget to separate the positive cables, and clean all sides.

You may have the Ignition Module ($$$)(under the coil pack) failing. Dealer can test it.

-George

Drive'em like you own 'em. - ....................04 DTS............................

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Do a "power balance check" where you monitor the RPM's while you override the fuel injectors to see which cylinders are causing the problem. If the bad cylinders are on the same coil then change that coil. If you smell plastic burning sometimes then it is probably a coil.

"Power Balance Check"

Start car

enter diagnostics

select "pcm override PS04"

press "warmer" button until cylinder 1 comes up

press "off" to maintain override, then select "PCM Data PD11" to monitor RPM's

press "cooler" button to shut off injector flow and note RPM drop.

If the RPM drops, then that cylinder is good, if RPM does not drop then that cylinder is the culprit.

press "warmer" button to move to the next cylinder and press "cooler" button again etc..

You may have to do it a few times to isolate the bad cylinders.

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I drove the car this morning and it drove a little better and had more power (like a V6) but it stumbles and hiccups at idle. I have to put it in neutral to keep it running and have to keep my foot buried in the throttle it keep up with traffic. I reset the codes and nothing has popped up yet.

I hope it's not the ignition module. I'll do the "power balance check" this evening. I won't be able to clean the battery terminals this week since I'm 200 miles from home and didn't bring tools. I'll have to drive the car back 200 miles or call AAA.

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I tried researching your problem last night Ed, but I only have the 91 and 96 manuals. I even went to this link and the P081 code just died >> http://www.cadillacforums.com/forums/north...-right-now.html

A google search did not turn up anything.

Why dont you go to a parts store and buy a wire brush and 5/16 wrench to clean the terminals

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks for researching the problem Mike. I also read that link and I seem to have similar symptoms however, I did check the outputs of the MAP & TPS and I did not find anything out of the ordinary.

Code P081 has not shown up again.

The battery is inside the car and the terminals look new. However, the battery might not be in the best shape since after 6 months of storing the car, it was completely dead and I had to charge it. I probably should have disconnected it. I'll try tightening the terminals tonight.

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Thanks for researching the problem Mike. I also read that link and I seem to have similar symptoms however, I did check the outputs of the MAP & TPS and I did not find anything out of the ordinary.

Code P081 has not shown up again.

The battery is inside the car and the terminals look new. However, the battery might not be in the best shape since after 6 months of storing the car, it was completely dead and I had to charge it. I probably should have disconnected it. I'll try tightening the terminals tonight.

That is possible, once the battery is dead, it never gets back to 100%, if you have a dead cell it will create havoc. My 91 would not pull away from the curb with a battery with a dead cell, but it needed to be jumped.. once jumped, it would run, but when I gave it gas, bam dead... new battery solved the problem.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The battery starts the car fine and holds charge. I let it sit a week and it started fine. I'm not saying the battery is not bad or degraded, but this car has a special kind of battery that has vent holes in it which hooks to piping that vents it to the outside. I don't know if this battery can be found anymore so other owners of this car are using gell batteries which are costly.

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Alright, the car ran much better this evening but still stumbles at idle and high loads/low rpm's. It is now starting to feel like a V8.

I performed the "Power Balance Check". I shut off each cylinder and I could feel a definite miss/shake when I would disable each individual cylinder. So it looks like each cylinder is firing properly. Since the engine passed this test, it means all the coil modules are good. Would this also mean the "ignition module" is also good?

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I would think that if you you notice a RPM drop on each cylinder when you disable the injector for the respective cylinder, the ignition module and injectors are OK. If the problem gets worse as the engine heats up, the ICM could be acting up. I realize you are a long way away from your tools but have you checked the fuel pressure? After studying the posts, I am starting to think the fuel pump is on its way out.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Alright, the car ran much better this evening but still stumbles at idle and high loads/low rpm's. It is now starting to feel like a V8.

I performed the "Power Balance Check". I shut off each cylinder and I could feel a definite miss/shake when I would disable each individual cylinder. So it looks like each cylinder is firing properly. Since the engine passed this test, it means all the coil modules are good. Would this also mean the "ignition module" is also good?

Well, not really. To rule out the coils the car has to be stumbling at the time of the "power balance test". It took me 6 months to isolate a coil problem. Mine finally got to the point where the car missed all the time. Then I smelled plastic burning and opened the hood to find a lot of smoke (coil finally burned out). The only way to rule out a coil is to switch them out 1 at a time (with a known good one), then drive it to see if the problem goes away. I remember switching out plugs, wires, fuel filter, FPR, cleaned phenolic plates, cleaned throttle body, and checked for vacuum leaks. It drove me nuts, but I learned a lot about the Northstar in the process and was at awe of its design. Boy, it did really run good when I finally changed the coil.

My symptom was slight miss on light acceleration. I think I have the same problem with my 97 Deville now. I discovered it last night so here we go again.

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Well, not really. To rule out the coils the car has to be stumbling at the time of the "power balance test".

OK, I get it. The engine usually only stumbles at idle and at low rpm/high throttle. When I do the "power balance test", it raises the rpms and the engine smooths out.

One other thing it could be is a bad EGR. The symptoms are very much like an EGR valve that is stuck open. However, I get no codes. Can I remove the EGR and somehow plug the hole and see if the symptoms go away or change?

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Well, not really. To rule out the coils the car has to be stumbling at the time of the "power balance test".

Can I remove the EGR and somehow plug the hole and see if the symptoms go away or change?

I do not see why not.

The saddest thing in life is wasted talent

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Well, not really. To rule out the coils the car has to be stumbling at the time of the "power balance test".

OK, I get it. The engine usually only stumbles at idle and at low rpm/high throttle. When I do the "power balance test", it raises the rpms and the engine smooths out.

One other thing it could be is a bad EGR. The symptoms are very much like an EGR valve that is stuck open. However, I get no codes. Can I remove the EGR and somehow plug the hole and see if the symptoms go away or change?

If the EGR valve was stuck open, it would set the EGR pintle position failure code.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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OK, I get it. When I do the "power balance test", it raises the rpms and the engine smooths out.

When you do a "power balance test" you are shutting off the fuel to each cylinder one at a time. If the fuel is shut off, the RPM's should drop. If it does not then that cylinder is not getting fuel.

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I haven't found the problem yet. Here is what I have done:

1. Removed each spark plug boot from spark plugs to check that oil had not filled spark plug cavity.

2. Reseated intake manifold and re-tightened.

3. Tested EGR Valve by going to PCM override. As soon as I would manually open the EGR valve, the engine would decrease in RPM's

4. Removed EGR to visually check it. It looked fine and seemed to be seating correctly.

5. Tried to test fuel pressure with a tire pressure gauge but it did not fit. Too bad Autozone doesn't loan them out. I will have to buy one from Ebay.

The next thing I'm going to check is the FPR. I going to get the car warm, then turn her off then turn the ignition back and let her sit for 3 minutes. I'll turn off the ignition again then turn it back on for 3 minutes. I'll repeat the procedure 3-4 times then attempt to start the engine. If the engine won't start, then it means it is flooded and I have a faulty FPR.

The engine is running a little smoother at idle but it still stumbles. When the car is still warming up, it runs very smooth but once it warms up, it starts to stumble at idle. Also, if I floor the accelerator from a standstill, once the engine reaches about 5000 rpm, I loose a bunch of power almost like I have hit the rev limiter. The RPM's do keep climbing to red line but it climbs much slower than it should - about like a 4 cylinder. There's a very definite RPM that this happens and it feels like several cylinders have been turned off. Could this be FPR related?

OK, I get it. When I do the "power balance test", it raises the rpms and the engine smooths out.

When you do a "power balance test" you are shutting off the fuel to each cylinder one at a time. If the fuel is shut off, the RPM's should drop. If it does not then that cylinder is not getting fuel.

The RPM's dropped for every cylinder that was tested.

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Does not sound like FPR to me. Sounds more like electrical including stuff like faulty PCM and ignition. Those components are known toact up when they warm up.

The saddest thing in life is wasted talent

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I also did the following today. Nothing has made anything better or worse.

1. Checked the battery connections and re-tightened them. The battery is inside the car behind and it as well as the connections look brand new.

2. Added some Lucas fuel treatment / injector cleaner into the fuel

3. Performed the Sea Foam treatment. It made a lot of white smoke but after all was done, it runs no better.

4. Performed FPR test by turning on the ignition on for several minutes, back off then back on several minutes. Engine started right up. It did not flood like what should have happened if the FPR was bad. I don't know if I can conclude or not if the FPR is good or bad.

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Ed, have you misted the wires after dark to see if they are arcing on the metal parts. Your problem sounds more electrical. My 97 is missing on acceleration now. I check the wires at night and found some arcing. I removed the cover and found a few spark plug wires against the new stainless steel fuel rail. I rearranged the wires and it did good for a while but then it started again so I am going to have to dig a little deeper.

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Update:

Paul T was correct. Thanks!! It turned out to be the coil. Whew!! What a relief.

As I was removing my coil pack, I noticed one coil which had a corroded contact. I brought the coil pack to Autozone and they tested them all and the coil that had the corroded terminal contact had an open circuit across the terminals. I bought their $29 coil, stuck her on, fired her up and the problem was fixed. The engine idles very smoothly and has plenty of power to spare.

I had originally thought it was a coil or FPR but what threw me off what that it passed the power balance test with flying colors. It was firing fine on each cylinder at fast idle. Also, my gas mileage was normal. I was still getting 24 mpg on the freeway.

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