: '98 STS stumbles and misses (NO CEL)



William Miller
10-27-09, 03:00 PM
We noticed this intermittently over the past month or so and now it's getting worse.

I read the following codes, but none seem applicable.... At least for my novice diagnostic experience.

AMP u1255 class 2 communication malfunction
AMP u1064 Loss of Communication with DIM (Dash Integration Module)
AMP u1128 Loss of communication with IRC (Integrated Radio Module)

PCM These are in History and may have something to do with the loose plug connection I found after I did the headgasket job.

PCM P0603 Control Module Long Term Memory Reset
PCM P1520 Transmission Range Switch Circuit
PCM P1527 Transmission Range to Pressure Switch Correlation


RFA B3108 (Current) Transmission Syncronization Failure

RIM B1009 (Current) Rear Integration Modual EPROM Checksum Error
RIM U1255 (History)



The engine seems to stumble at idle worse when in "Drive".
The car shakes.

I haven't spent much time looking at things yet, but, decided to submit this post while I was looking up the codes.

Could this be a symptom of a crank position sender going bad?
I think the car has a cam position sensor, does it have both?
Thanks for any thoughts on where to start looking.!

Ranger
10-27-09, 06:31 PM
You have 2 crankshaft position sensors and 1 camshaft position sensor. I would suspect plugs or wires.

William Miller
10-28-09, 08:25 AM
Thanks, now I remember them on the front/or left of the engine under the manifold.

Is one for speed and the other for TDC?
What is the failure experience?
Do they just completely quit or get weak over time?
Can they do this without throwing a CEL?

I ask because I was helping someone with their Mercedes and the engine would completely quit once it got up to near normal operating temp.
Once it cooled, it would start right up. The crank sensor was the culpret, but it didn't throw any codes.

Your right on the plug wires and the plugs.
It's quite possible I've had a mice attack, but that usually happens once it gets a little colder arround here.

The plugs are recent (probably less than 5,000 since I did the head job.)
Their condition would help me diagnose where (if one or two particular cylinders) the problem is.

The symptom seems like more than one or two and it's not a consistant miss.
More like it misses a few times and then runs smooth. Like that off and on.

Time to check the wiring and for plug wire arking, I guess.
Battery terminals and grounds?
Anything else?

Thanks again!

Submariner409
10-28-09, 11:26 AM
If one CKP acts up the car usually has an intermittent low-speed stall during warmup or when slowing as for a turn. If both CKP's (crankshaft rotation angle and ignition trigger) act up the ignition system defaults into a fixed (10 degree) advance lock. If the CMP dies (piston position reference), the car flat won't run. Some CKP's (Hall effect devices) will slowly degrade, while others fail totally. There's no rhyme nor reason. A failing CMP or CKP may or may not throw a code and CEL.

Make very sure the plug wires are connected to the coil towers as shown.

Remove all 4 coils and clean the contacts and ICM connector and ground.

Google "waste spark ignition" to learn why the wire polarity is so important.

William Miller
10-28-09, 12:00 PM
Thanks for the quick reply and all the info.

What's the best product / method for cleaning contacts, connectors.

I have some electrical parts cleaner / spray. But I've never really felt it did much other than dissolve grease.

The wires should be in the right places because the car was running great after I did the head gasket job. The drawings are great resuorces as I will go over it all again.

I don't need it yet, but is there a pin-out for the pcm or a wiring diagram avalible for this ignition section? If the simple things don't solve it, I'd like to check continuity and shorts.

How about a bench test for the sensors?


Thanks for the help!

How's the weather down at Kent Island?

Submariner409
10-28-09, 04:33 PM
We're a week behind you guys, leaf-wise. Ol' Sugar Loaf must be gorgeous right now........May be headed for Sharpsburg/Antietam next week.........

Standard old Radio Shack electronics or tuner spray is fine.

Others with your ICM under the coils have had ground continuity problems.

Your best bet now is to either find a Helm/GM service manual on eBay or subscribe your car to www.alldatadiy.com for a year or more.

Ranger
10-28-09, 05:54 PM
What's the best product / method for cleaning contacts, connectors.
I have some electrical parts cleaner / spray. But I've never really felt it did much other than dissolve grease.
Brakleen works very well.