weird bogging down issue

[3100 MPFI]

Okay. I replaced the DIS and coils, and it still does not run right. I used the DIS and coils from my 1995 Cutlass Supreme 3.4 DOHC (this is probably the ONLY time I have EVER said that I am GLAD that I have a 3.4 DOHC). I put the DIS and coils in and it does the same thing. After about 10 minutes of sitting there idleing, it starts bogging down and stalling when you give it throttle.

[3100 MPFI]

I had an ephinany.

The ECM is bad.

Turned the key on, but the SES light was OFF. Thinking the bulb might be burned out, I stuck a paperclip in the ALDL. No SES light, and NO COOLING FANS.

When I turned the key on with the paperclip in, the IAC went nuts (I know it was the IAC because when I unplugged it, the noise stopped).

Anyways, I am going to go hunt down a spare ECM, and see how it does.

[3100 MPFI]

Okay. This is weird.

Replaced the ECM. Tried 3 other ECM's and 2 other chips. Still doing the same thing.

I guess it is time top get the book out. Whatever this problem is, it is effecting the ECM.

When I put a paperclip in the ALDL, and turn the key on, there is NO LIGHT (the bulb MIGHT be burnt out), but there is also no COOLING FANS (but when I bypass the relay and jumper the terminals, they DO turn on, so the cooling fans DO WORK). Also, the IAC goes NUTS and starts clicking and vibrating. I know it is the IAC because when I unplug it, it stops making noise.

Where is my book when I need it?

[3100 MPFI]

Okay. I pulled the dash out to reaplce the SES light bulb. I figure that I can't really do any proper diagnosis until I know if the light even works. The tests that I had done at that time was all leading up to ECM problems.

I got the bulb in, and checked for codes, and the SES light DOES flash the codes, but the fans do NOT turn on. The IAC still buzzes.

Anyways. Get the bulb in, and right away I get a code 34. I will look into that tomorrow.

After starting the car, I get a code 43 right away. Feel back behind the engine, and sure enough, the knock sensor wire is unplugged. Turns out the connector has broken off. Tomorrow, I will get under there and replace the connector, then start troubleshooting the MAP sensor.

I am GOING to get to the bottom of this. This car has pissed me off for the LAST TIME, DAMNIT.

[3100 MPFI]

finally figured it out. It was a combo of 3 things. The knock sensor connector had broken, so it was unplugged, the MAP was bad, and the ECM was bad.

I stuck a new knock sensor wire in there, I dug up an old MAP sensor (I thought it was bad, but so far, the car has not stalled or surged), and then I stuck my 1993 ECM in there with the 1990 memcal.

So far, it idled for about 15 minutes, then I decided to drive it around the block. No surge, no sputter, and most importantly NO STALLING.

I am going to take it on a long drive tomorrow.

[davida1_hiwaay_net]

Glad you have it fixed!! The MAP sensor alone will cause the whole problem. The ECM will not flag the MAP sensor as bad if the signal is not short circuted; and if the signal moves around some. The sensor signal can be horribly incorrect, but as long as it is not shorted or stuck at one fixed voltage, the ECM will assume it to be correct and inject a faulty amount of fuel based on the faulty MAP signal. Therefore you get the malfunction!

What was wrong with the ECM? Just curious!

[3100 MPFI]

ecm would not go into diagnostic mode. It also will not turn on the cooling fans. I could not hook up my computer (still have not got that adapter for my cable). I did all sorts of test, and several were coming up bad ECM.

I have a couple spare ones anyways, so that was no big deal.

[torq455]

congrats! awesome find! yaaay!

[davida1_hiwaay_net]

IIRC that year range of your car had a history of bad ECM's. You could hit on the ECM and the lost functions may return temporarily. Probably bad solder connections.

I've had 1 ECM failure. I took my TBI converted 72 Nova on a 9 hour trip from AL to TX and halfway home started to have problems. Car started to surge and high-idle and set TPS and MAP codes. It was running "pig-rich" and finally died. Took ECM out and water ran out of it!!! Seems the 30 years old A/C leaked water on the ECM and screwed it up!

After drying it out the car ran OK but with hesitation on throttle response and TPS code. Scan data showed TPS stuck at 45% regardless of actual voltage on that circuit. Replacement ECM corrected this. Lesson learned and ECM relocated...

[3100 MPFI]

the car didn't have the original ECM. When I got the car, it had a 1993 ECM with the 1990 memcal in it. I replaced it with a 1992 ECM, but that is the one that went bad. I now have a different 1993 ECM in there with the 1990 memcal.

So far so good. My fuel economy is also back up to where it should be. When all this stuff was going bad, it was getting about 20 mpg, but now, it is back up into the 40's like normal.

[3100 MPFI]

vid of the fuel economy now that it is running right.

I have check it, and confirmed that it is really getting that.

http://s174.photobucket.com/albums/w86/riven2129/video/?action=view&current=stefueleconomy1.flv

[torq455]

maybe you should go 65 mph for real highway mpg.

[3100 MPFI]

once I get the car registered, inspected, and insured, sure thing. I did that back when I was working in Houston, and it was getting about 52 MPG at 67 mph.

[1994KlrWhaleOlds]