: Northstar barely running

11-26-05, 12:57 PM
The Northstar in my 94 Seville (175k miles) has been almost flawless over the last 100k miles. There'd been no sign of any problem before starting her up last night. She immediately began missing randomly on all cylinders; reminding me of a vacuum leak in a carburated engine. As I forged home, she continued missing and idling very rough. I had to keep my foot on the gas to keep her running at idle. A handfull of times the idle surged up to 2500 (without my help), afterwhich she'd run good for 15-20 seconds. Part way home the dash LED display displayed, "Traction Control Disabled". The missing and roughness got worse the more I drove. By the time I got her home, it was difficult to keep her running.

This morning I started her up (problem persists) and got the following CURRENT codes out of her: P023 and A047. From the list of codes on this site, my P023 code looks interesting. The description of that code on this web site says, "Electronic Spark Timing (EST) Signal problem [EGR]".
After lunch I'm going out to look for vacuum leaks. Any ideas or input would be greatly appreciated.

11-26-05, 05:22 PM
Have you cleaned the EGR and rodded out the "mouse holes" in the intake?

11-26-05, 11:51 PM
Ranger, I'll do that tomorrow and let you know. Thanks, Jeff.

11-27-05, 04:29 PM
Ranger, I've located and removed the EGR. Nothing jumps out at me as looking like it needs to be cleaned. The piston in the valve moves freely and the other hole in the valve (a hair broader than the one with the piston), though coated with exhaust soot is open. Both holes in the intake are open as well and don't seem to have any more than a thin build up of exhaust soot. What kind of cleaning procedure should I do? Or does she sound clean enough?

Also, if anyone has any idea of what voltages and currents are applied to the valve, I have access to a variety of power supplies to test the valve and can test it at work tomorrow.

Thanks, Jeff

11-27-05, 05:43 PM
Everything sounds good. I have never had a '93/'94 but my understanding is when you remove the intake cover there are "mouse holes" that need to be rodded out. That seems to be the clog point . Do a search for "mouse holes". You should come up with a lot of reading.

11-27-05, 11:18 PM
Your ignition module is bad, or related wiring or connectors aren't connecting properly.

I'd get some "electronic contact cleaner" from a parts store, remove the connectors, and spray them down good... let everything dry, and reinstall the connectors. See if that doesn't fix it (probably won't, but it wouldn't hurt to try).

After that, I'd replace the ignition module with one from a junkyard ($40).

11-28-05, 12:29 AM
Yeah, this sounds more like Ignition Mod. Related than EGR. Unless EGR was stuck full open.
If "mouse holes" were plugged up, then exhaust gasses would have problem getting to the intake chamber (even with the EGR valve open). That would not make the car want to stall. It is overabundance of exhaust gasses in the intake which make the engine want to stall.

Well, this could also be related to an electrical EGR problem (keeping the EGR valve open). Too bad that the codes are so vague.


11-28-05, 10:07 AM
I don't know who added the "[EGR]" to the end of the text there, but the code is for an EST error. The computer is trying to control the timing, but the ICM is not listening. This could be due to a break in a wire, or a bad ICM. Since you say it's barely running and it happened suddenly, I'm putting money on the ICM.

11-28-05, 12:54 PM
Thanks for the input guys.

Just to make sure that I understand exactly which part you're talking about; it's the four coils mounted on the rear valve cover that the plug wires run to. Is that correct?

11-28-05, 01:01 PM
Guys, can anyone tell me where the 94 Seville keeps her fuel filter?

11-28-05, 02:36 PM
The ICM is the part that the four coil packs plug into. The plug wires are connected to the packs and the packs are connected to the ICM. You have the correct location.

The fuel filter is located just under the car, behind the back driver's side door, before the rear wheel well.

11-28-05, 02:37 PM
Thanks for the input guys.

Just to make sure that I understand exactly which part you're talking about; it's the four coils mounted on the rear valve cover that the plug wires run to. Is that correct?

that's correct. The coils each have 2 bolts holding them on to the ICM, in case you need to move them over to the new one. Order is important to keep the numbers painted on them correct.

The ICM has 4 plugs on it, I believe. Try removing and spraying those with the electrical contact cleaner/wiggling them around/etc. Make sure they're dry before plugging them back in. Maybe a bit of grime is giving you some contact problems, but more than likely the module is bad.

Daniel Almestica
11-28-05, 05:10 PM
I had the samething happen on my 94 etc. I had to change 2 of the four coil pack and the car ran like new. not a big thing good luck

11-30-05, 04:13 PM
I've read many similar posts and the cause is generally coil packs. Be sure to post findings when repaired. Good Luck.

12-22-05, 11:17 PM
Guys, I've finally freed up some time to run down another ignition module. I rounded up enough neighbors to push her up into the garage and I replaced the ignition module. It made no difference. Problems are identical to what they were with the previous ignition module.

If anyone has any other ideas, I'd like to hear them.

Thanks, Jeff

12-22-05, 11:49 PM
The code description says "Electronic Spark Timing signal problem." Could this be a crank or cam position sensor issue? ewill3rd, do you have any thoughts on this one?

12-23-05, 04:29 AM
Your code P023 was set because the PCM did not detect any ignition pulses. When this happened, the PCM disabled the egr solenoid and disabled spark timing control. Instead, the engine will start and run on base timing.

I would check all the wiring to and around the ICM, like Eldorado1 said.

By the way, A047 is low refrigerant in your a/c system.

12-23-05, 09:31 AM
ugh... I wrote this huge post, and then I closed the window. :banghead:

Lets try this again.

Code P023 will set under either of the two following conditions:
1) 4x reference pulses are being recieved by the PCM and the bypass line is low, and the PCM detects pulses on the ignition control line. This could be caused by the bypass line shorted to voltage, or a faulty ignition control module.

2) 4x reference pulses are being received by the PCM and the bypass line is high, and the PCM does not detect a signal on the ignition control line. This could be caused by an open or a shorted to ground ignition control line or bypass line open or shorted to gruond.

Both of these lines lead to the "big" connector on the ICM, next to the "5/2" ignition coil. Start checking for corrosion, melted wires, etc...

12-23-05, 08:11 PM

A thanks all around for the input. I can tell you that all connectors on the ignition module are clean. I've just gotten home from work and we're loading up the kids and presents and "off to grandma's house we go". When we get back Monday, I'll start at the ICM and work my way back as far as possible unpluging and cleaning connectors.

If anyone knows of an on-line wiring diagram for the 94 Seville's ignition, I should be able to probe and test shorts and opens as you've suggested.

I hope you all have a very Merry Christmas.

Thanks again, Jeff

12-23-05, 08:34 PM
Make sure Grandma doesn't drink too much eggnog. Those reindeer don't give the right of way.

01-22-06, 05:42 PM

This particular grandma has been my mother-in-law for 23 years. I learned early on that she believes that justification is by faith plus NEVER EVER having any additives in your egg nog. She's great though; as long as I keep my English and German Ales out of sight when she comes to visit.

Back to the Seville... I've managed to clean the four electrical connections at the ICM and the two connections at the Crankshaft Position Sensors (CPS). My results were exactly the same as described in this thread's inaugural post; she had fire, but wouldn't start. Between the local O'Reilly's and Autozones' I managed to scare up one CPS. I replace the lower CPS with the new one. Now after 15 seconds of cranking she fires up and the original code, P023, is gone. I do have a new set of symptoms (below); keep in mind, the only thing that's changed is that the lower CPS has been replaced. Depending on what you guys suggest, I'm planning on replacing the other CPS when the O'Reilly's gets one on Monday.

She fires up after 15 seconds of cranking (she wouldn't start before the new CPS). She idles between 900 and 1800 rpms while cold; I've yet to warm her up. She now throws two different codes; P012 and P053. Looking them up on this web site, they both have to do with the distributor. Since the Northstar doesn't have a distributor, I'm hoping you guys can tell me what to make of that.

P012 (E012) ... No Distributor Signal
P053 (E023) ... Distributor Signal Interrupt
Thanks in advance, Jeff

01-22-06, 07:59 PM
P012 will set because 4x reference pulses are not being sensed. Engine will start after extended crank because the 24x reference pulses are being recieved. Fuel delivery to injectors is triggered by pulses. If the pcm doesn't sense the 4x, it will switch to the 24x.

P053 is fairly much the same thing...no 4x reference pulses.

Have you checked the 20A fuse in the engine compartment fuse block labeled DISTR. That is for your ICM. Most tests lead to your ICM. You mentioned you replaced yours. With a new one, correct? Next would be a short or an open. If you don't find anything there, it could be the pcm itself.

If you can use a multimeter, I can forward you a flowchart to look for the correct voltages and to check for shorts or opens.

01-22-06, 08:31 PM
Since it runs, and it's not the ICM, it has to be the wiring. If you can wait a bit, I can get you a schematic for the ICM wiring, if someone hasn't posted it yet.

01-23-06, 12:11 AM
Here you go, probable wiring problem highlighted (sorry, had to rotate it to post it).. Check them for continuity between PCM and ICM.

01-23-06, 09:47 AM

Thanks for the replies.

I have replaced the ICM with one from a wrecking yard. If it is bad, then my original ICM and my 'new' one have the exact same problem, because they behave identically both before and after the new lower Crankshaft Position Sensor (CPS). I can use a multimeter (use an oscilliscope at work all the time); so yes please forward the flowchart of voltages. Perhaps that combined with eldorado1's schematic can provide some good information. The 20 amp DISTR fuse under the hood is not blown.

Considering the 4x and 24x pulses, I have some questions. Are these pulses timing pulses that coorespond to input from the CPSs? If so, does perhaps the bottom sensor send the 24x pulse and the top sensor send the 4x pulse? If so, since she'll run off the 24x pulse, that would explain why she started running when I replaced the bottom sensor. If I'd replaced the top sensor, would the 4x pulse be present and not the 24x?

Thanks again, Jeff

01-23-06, 10:04 AM

Only part of the schematic you've posted is there. This would be great information to post on this board somwhere. If you can email me that page, I'm at jssmith6@yahoo.com.

Thanks, Jeff

01-23-06, 12:09 PM

I will email you the flowchart I have and a diagram that goes with it.

01-25-06, 05:45 PM
i just had the ERG replaced in the eldo in my avatar, same description you gave 109K car runs amazing now

05-31-06, 09:27 AM
Update and big thanks to all, especially eldorado1 and Eldyfig. Using the schematics and procedures they provided, I narrowed the problem down, not to the $1100 the dealer wanted to replace the ICM and CPSs, but to the PCM. Finally located one with the correct SERV# in a wrecking yard and plugged it in last night. After sitting dormant for six months, I cranked her for five or six seconds and she fired right up.

Thanks again guys.

05-31-06, 09:35 AM
Interesting! Glad you got it fixed. So... can I take the broken PCM off your hands? :D

05-31-06, 06:26 PM
Eldorado1, I don't suppose I have any use for the bad unit. Let me get her back together and running smoothely (she's missing and a few other sitting-idle-for-half-a-year things) and if I don't need it for anything you can have it.

05-31-06, 07:13 PM
cool! I'll happily pay shipping for it. I'd like to take it apart and compare it to some others I have...

06-01-06, 01:21 AM
I had similar problems on different circuits that were solved by a new PCM. I think the reference voltages get screwed up in the PCM sometimes. My conclusion is that if you follow the diagnostic chart in the FSM and replace the identified failed part and verify the wiring to the part, that leaves only a faulty PCM as the culprit. BTW, I keep a spare PCM in my trunk after I had mine go haywire out of the blue. Thanks for the update.

06-01-06, 08:27 AM
eldorado1, the system won't let me PM you until I have 50 posts. With all the trouble we had before I wised up enough to get rid of the wife's Catera, I can't believe that I don't have a million. If anyone ever offers to even GIVE you a Catera that's in great shape for no charge, turn and RUN:rant2:

If you'll PM me your email address ...

06-01-06, 09:09 AM
That's interesting. I stayed out of this one because I don't feel like I know enough about the hard core diags in these cars but the reason I find that interesting is because this is about the 5th story I heard regarding this.

I heard of people being stuck on the side of the road in everything from a car with 20k and now to 178k due to a bad PCM. This is the first detailed description I've had of the symptoms but the PCM seems to be a week link in a wide range of model years.

When I bought my 01 we got to talking about OnStar and the salesman was telling me that a friend of his was stuck with a bad PCM and OnStar diaged it remotely for him and got him on his way in a few hours. That was also an 01, you have a 94.

I wonder, if there is a problem, if and when it's been resolved. It would be interesting to know exactly what internally failed.

06-01-06, 10:17 AM
electronics are fickle.

Anything could cause one to go bad... heat, static, a bad solder joint, a bad chip... The automotive environment is tough on electronics. You've got high voltage and RF noise from the spark plugs, heat from the engine or outside if you're down south, vibration, the extreme cold up north... Getting 10 years out of something is pretty good in my opinion.

06-01-06, 11:10 AM
codewize, I am an embedded software engineer and over the past 19 years have written software for everything from factory robots, to laser tag guns (working on a video projector currently). Most likely eldorado1 will find that a component, probably an IC chip, has gone bad. I've seen military applications in which a printed circuit board encased in a protective compartment can survive prolonged jolting much greater than our beloved Cadillacs will ever see (even in a 60mph head on collision).

I say all that to say, yes, it was well within the capability of early 1990's technology to build a board that will survive the somewhat harsh environment of a PCM. If PCM failures are occuring at the rate you've observed, then Cadillac messed something up designing/building the PCM.

06-02-06, 10:22 AM
I say all that to say, yes, it was well within the capability of early 1990's technology to build a board that will survive the somewhat harsh environment of a PCM. If PCM failures are occuring at the rate you've observed, then Cadillac messed something up designing/building the PCM.
jss, you really had me going. I thought you were saying something very scientific and quantitative and then you spun right off into never never land. In particular, I'm not sure at all what PCM failure rate codewize has observed. It's like saying that since I know of people breaking iPods, all iPods are easily broken. This may or may not be true, but without the numbers, we don't know anything about the quality or durability of the PCMs. And this comes from a guy who carries a spare.

06-02-06, 12:45 PM
delzy, I'm with you; :yeah: . In fact, I thought I said that. Well, whatever I said, it was intended to mean pretty much the same thing you posted

06-05-06, 11:38 AM
Yes I agree. I don't keep tabs on this I have just heard of several people having this problem in the short time I've had my N*. That certainly doesn't mean there is a problem. I just think it's interesting at least.

I guess I was originally digging to see if anyone else felt that there was an issue.

06-07-06, 03:25 PM
Just checked in, haven't been here in a while...

Glad to hear we were able to offer some help and you car is going again. Cool deal!