93 sts just turns off intermittant

[paulbaumgartner]

I gave my daughter my trusty reliable ol' 93 STS last year. I feel good knowing this tough, good looking, and once reliable car, may give her a fighting chance in the event of the ultimate bad scene. I really want her to drive this car at least until her graduation next spring while she gains more driving experience.

Recently (about three or four weeks now) it has developed a stealthy failure symptom. You never know if or when it decides to strike. On occasions, the engine simply turns off. Doesn’t give any warning, just "motor off now thank you". When it is running it starts fine and kicks butt. When it quits you coast to the side of the road, restart the car, (this may take a few minutes) and continue your blissful motoring excursion. The driver information display is suspiciously silent. Codes you ask? Only one. P032 H. History only, never current. The only conclusion I can make is maybe the map sensor and the fuel injectors are powered for the same source, the pcm....

On a recent test drive, I finally caught this problem during one of its "moments". It had stopped running and was not restarting properly. My daughter was with me on this test drive and we coasted into the rear entrance of a Wal-Mart. With fuel pressure gauge and timing light in hand, I spring into action. My daughter was slightly less than impressed and appeared to be loosing confidence in the reliability of the car calling into question my street credentials as a mechanic. The stakes are high. Not to mention, my ex is using this as an excuse to tee-off on me as being a cheap-skate, low iq, dad that cant fix sh%&*. Actually she wouldn't be so bitter except my daughter totaled her car when the STS was awaiting repairs (an alternator replacement about 6 months ago that I paid a shop big bucks to replace). Oh the irony. I don’t blame my ex for not wanting to loan my daughter her car and I really could care less what she thinks about my technical skills anyway. My little angel is the quintessential teen-age driver. Please be on the lookout.

Fuel pres-OK, Ignition-OK. The only code that is indicated is the old P032 H that is logged each time the engine shuts down. I have checked the wiring harness going from the PCM to the intake manifold. Continuity good. I think it is the PCM shutting down the injectors. I have a service manual/cd with detailed schematics and diagnostics. Unfortunately I live in Dallas and she lives in Nashville and this last trip I accidentally left my service cd/manual in Dallas and ran short of time to diagnose the problem further.

I make the most of my trips to Nashville making the repairs on the car myself that are not cost effective to pay a shop. I rebuilt this motor about two years ago anticipating my daughters’ entry into the motoring population. This car gives me a reason to hang out and do a little cruising with a really fine young lady. I am just a dad doing the best I can here. If you know what this problem is, please respond in kind. I am going to attempt to source a PCM module and go this weekend for another attempt to secure the confidence of a VIP in both car and mechanic.

[MAC]

Looks like you need to replace the map sensor.

[paulbaumgartner]

Thanks for the reply. It has been my experience that in the event of faulty map sensor (shorted or open) the "service engine soon" light comes on, but the engine doesn't cut off. It is supposed to just go into an open loop run mode. I wont rule anything out at this point though.

Thanks

Paul

[Cadillac Jim]

P0032 - Heated Oxygen Sensor (HO2S) Heater Circuit High Voltage Bank 1 Sensor 1

This problem, like the bad MAP sensor, puts the car in an open-loop mode. Note that you are calling out P032, not P0032. Make sure that you are getting the right code.

It sounds like a fuel pump or FPR to me. Less likely suspects that can cause this problem are engine position sensors.

[paulbaumgartner]

Thanks Jim,

I was like you thinking it would be fuel related. The gauge told the truth though, approx 45psi constant. Starting, runnin and even when it is refusing to start immediatly following sudden shutdown. Another tidbit... With the fuel preasure guage connected, I run my bleed off hose directly into the plunum past the throttle plate and the engine sputters to life as long as I keep squirting fuel directly. Low class, but effective. Bottom line, injectors not firing.

It is the lack of failure codes that confuses me. You unhook one little plug on this thing vomits codes all over itself.

Thank you

[Cadillac Jim]

Are you checking fuel pressure before or after the FPR? Check the wiring to the fuel injectors.

[paulbaumgartner]

I was checking fuel preasure at the input to the fuel rail. Also, I didn't have my detailed schematics with me last weekend. I am going back either this or the following weekend with my wiring diagrams in hand. It appears the fuel injectors are supplied power from the engine fuse compartment and are switched/activated by an active low from the pcm. The interesting thing is there are two fused supplies to two banks of four injectors. If it was hitting on four I would know that, but all eight are dead when it is failing.

One more thing, there was a code P095. Not all the time but stored occasionally. P095 is not listed in my factory service documentation for the 1993 Seville. Any Thoughts?

Thanks for your thoughts,

Paul

[Cadillac Jim]

Whoops, I've been looking at OBD II codes. The 1993 model year uses OBD I.

P095 (E095) .................................................. Engine Stall Detected

Now, that's what I call a code.

P032 (E032) ................................................. Open MAP Sensor Signal

That's why MAC suggested a MAP sensor. Mine gave some codes once and I had it in my hand and was just about to go to the dealer for another, and I decided to put it back and see what happened. It was fine, indicating that it was just dirt in the connector or some such. Since it is intermittent open, a loose connector seems likely for your car too. However, due to the seriousness of the situation and lack of time to try things, I would have one in my pocket the next time I visited Tennessee. The MAP sensor is under the noise/heat cover (the plastic cover that says Northstar) on top of the intake manifold, toward the driver's side.

I looked through the 1997 FSM for more hints. The diagnostic process for engine misfiring says to check the injector wiring. The section on engine cranking but not running says to check the engine ground and the circuits between the connector and the fuse block. The engine ground is a real news flash.

If the whole car goes dead when it dies, look at the battery cable, including the grounds, the engine ground strap, and the battery itself.