1993 3.1

We have a 93 Olds Silhouette with the 3.1. Same as whats in the Transport...

What happens when we drive it is:

When I jump on the gas in park it accelerates throughout the RPM range with no problems. However if I gently step on the gas up to around 1500 rpm's the vehicle carries on and misses and rpm's drop.

While driving and pulling out normally the van seems to surge and buck from idle to 2500 rpm. After that the rpms are to high to notice any missing...

I have replaced the wires, cap, rotor, plugs and O2 sensor.

I also got check engine light code 42. Which is Electric Spark Timing. The book says the bypass circuit is open or grounded. A malfunctioning HEI module can cause this code.

There are a few things I am writing about in this thread...


1. Is there a way to find the exact problem or should I just replace the module and pickup???

2. What is the correct way to set the timing? The book says to disconnect this tan wire (which disables the EST) that runs along the pass. side near the shock tower. I dont have a wire there that is by itself.

3. What else is there??? What could be the problem? Could it be something with the fuel I overlooked??

The injectors have a good spray pattern so I dont think its that. I did NOT check the fuel pressure. Could it be the throttle position sensor, crankshaft position sensor,speed sensor,spark knock sensor???

My first thoughts on your problem were faulty EGR.

Mine is a '94 3.1
When the engine was cold or just restarted and in open loop it ran fine. Once it went into closed loop I would have an engine miss during light and part throttle driving. There were no DTC's.

I ended up disconnecting the EGR vacuum line and plugging the hose. My problem went away, and DTC 32 was set (as it should). It took several hours over a couple off weeks to eliminate the other possible cause of the problem before the EGR was singled out.

There is no EGR below 3% TP, above 50% TP, low vacuum or low engine temp.

As for DTC 42 there are four reasons for this DTC being set.

-Bypass 0V, any voltage on IC timing line (should be zero)
-Bypass 5V, 0V on IC timing line (should vary)
-Bypass open or grounded (as when timing is set)
-IC line grounded, in this case the engine will not run DTC may or may not set.

Current DTC 42 is cleared after each ignition cycle

There are two diagnostic charts and four pages of text in U body service manual to trouble shoot DTC 42, So yes you can find the exact problem. If it is a wiring fault repalcing the module won't solve DTC42

I agree about the EGR, and it is so simple to prove it right or wrong, and cost nothing.

Not the egr.

Changed that...

but how to test it or prove it???

OK...for a last test with the EGR, just do as NiteOwl said: disconnect the vacuum hose to it and plug the hose. You will get en error message but you will see immediately if it changes something for good. However, if it was blocked somewhat in an opened position, you would still have a problem...but you say it has been changed, so we can PROBABLY rule out that option.
But I have had something that ressembles your problem with my 3.8: dirty mass air flow sensor. After searching for a while - listening all those who bkamed the fuel pump, the fuel filter, etc etc - , I took that part out and noticed a thin coat of dust cooked on the hot wires in the air path that make that sensor work and cleaned it with an artist paint brush and alcohol. It is not specially fragile, but take care anyway. THis cleared my problem INSTANTLY and COMPLETELY.......
Well ...wait....as I am writing this, I just check my book...and the 3.1 does not use a mass air flow sensor: it uses a manifold pressure sensor, so my suggestion does not fill the bill....but a false manifold pressure reading could have same effect....or a lagging pressure reading due to a clogged pressure port..??? Well...I'd have to see this now...Anyway, those with a 3.8 may still keep my story in their mind.

...but....you do have a Throttle Position Sensor. THis is a potentiometer - a pot - that provides a voltage that is roughly proportionnal to throttle opening. I have had a problem with that too: it is easy to measure the output voltage (there are 3 wires: ground, hot (do not remember if it is 5v or 12v) those 2 are constant voltage - and the thid wire varies voltage with throttle opening. Mine would give erratic output: voltage at one throttle opening would vary - bad/dirty contact between the "wiper" and the resistance track. I was able to feed some cleaning agent - alcohol or WD40 - and it filled the bill. I do not remember what "hole" was available to introduce the solvent, tis is several years ago...and this is still the original piece of equipment - 11 year old --still functionning.

I had the vacuum totally removed from the EGR for a few minutes and no CEL. I also plugged the inlet on the TBI for the EGR and no difference there.

To me it kinda seems like bad fuel... but I have great spray out of the injectors and if I tromp on it the RPMS fly right up...and its been doing it for quite some time...just getting worse

I will play with the TPS next. Any ideas on the spark knock sensor or Crank position Sensor???

just took it for a drive.

Barely ran and allot of stalling. Had to floor it to get it to start. Also seems to surge when I hold throttle at 1000 rpm or 1500rpm...runs great when you go up a hill or give it allot of gas...

example...run (1 sec), tries to stall (1 sec), run (1 sec), tries to stall (1sec).

Going to buy a module and pickup. Have a spare TPS off another olds, going to try it to see if it changes anything...


also now I have error code 45 CEL...possible rich or leaky injector, high fuel pressure or faulty TPS or MAF sensor. Also check vacuum canister for fuel. Replace O2 sensor...(mine is only 2 days old)...

well I chenged out the TPS with another one that I had. Nothing. Now it doesnt start at all and theres NO gas present coming out of the injectors. No matter what TPS I put in it doesnt start. I did try to start it without the TPS plugged in. What I DONT know if I tripped some sort of breaker or safety mechanism. I would think now I need a fuel pump. What do you think???


Now I am going to get a can of starting fluid and I am sure it will start with that...if not Ill let you all know...

started with the starting fluid...

fuel pump fuse is good.
power TO the relay.
I cant seem to get power from the relay but will retry again....

I guess its possible for the relay to up and die but I wouldnt think slowly.

According to my diagram the ECM tells the relay to come on??? Then the relay is switched to allow power to the Fuel pump. Correct??

If I test the wire coming from the ECM I should have voltage there. Then the relay clicks and I should then have power on the wire going to the Fuel pump...

but why did this all of a sudden happen? Did unplugging the TPS do something to the ECM??

To check the fuel pump;
When its quiet, standing outside the van reach through the open driver side window and turn the key to run (not start). You should hear the fuel pump run for about 2 seconds.

Another option is to apply a fused 12V to the fuel pump prime connector in the engine compartment (key out of ignition). It is a red wire with a enclosed terminal located near the MAP on the air cleaner, follow the wires to the harness. Again listen for the fuel pump.

There are two "switches" to supply power to the fuel pump. The oil pressure sender switch and the fuel pump relay which is controlled by the PCM. The oil pressure switch is a backup to the fuel pump relay.

If you do hear the fuel pump, you'll have to figure why the injectors are dead. Did you run out of gas?
Remember DTC42...IC line grounded= no start

DTC 43 would be set for bad knock sensor system, PCM would set a fixed timing retard.

There is no crank sensor on the 3.1. The distributor reference signal provides RPM and crankshaft position to the PCM

Here's a long shot. A PROM not fully seated in the PCM can set DTC 42.

At this point I would step back, clear my head, the DTCs and start from scratch. Without seeing what's going on...

As for the EGR, you say you unplugged it for a few minutes and no CEL. Did you drive the van? If there was no CEL do you mean no DTC 42 as well?
You should have just removed the vacuum hose from the EGR and plugged it. Then gone for a drive. DTC 32 would be set only during driving (cruising) when the EGR is used. The PCM runs a diagnostic to check the EGR during (and only during!) cruise. This can take several miles, 10 -15 minuits of driving. If DTC 32 was not set then whatever you did did not test EGR function (or malfunction as the case may be). My EGR did not leak so no effect on idle or heavy throttle use. It passed all test according to the manual, although the vacuum hold test was a close one. It had come out of calibration and during operation it was causing an engine miss.

Unless you zapped the PCM with static while messing with the TPS, then nothing should have changed. Worst case, one of two possible new DTCs and a van that runs on a default TPS value.

Could be a wiring harness problem...

Just out of curiousity, what book are you using?

Will check today...

Haynes 90-95