92 MFI stuck in limp mode?

[poptones]

I just got a 92 Beretta with 3.1MFI and auto trans. It is my first GM car (the only new car I ever bought was an 87 Mustang which I loved and drove hard til it died at 250,000 miles) and I am surprised by how much I like this little beretta. It seems like a solid little car in spite of the fact it needs truts, shocks, ac work, torque converter (lockup is unplugged from trans) and (apparently) a new 300 stinking dollar EGR valve.

When I first got the car it had been sitting about a year. It was started regularly but not driven much the last year and a half, but before that it ran quite well and I know it got good mileage because my father bought it from his cousin and they once drove it about 500 miles on a tank of gas. The motor sounds good and on the few rare occasions it has found its way out of limp home mode it is surprisingly peppy. When I first got it the motor was running very poor and erratic. It never died on me but idled rough, had little power, surged a lot and seemed to drink gas. A friend told me it was probably an egr valve, he took it off car, we cleaned it and the ports and replaced it, changed oil and that other stuff you do with a new used car, didn't help.

I decided to drive it and see if things got "burned in" since it has been sitting., I set out on a 100 mile drive, i decided if it was egr maybe disconnecting it would help, so i unplugged it. It did very ok on the trip, not too bad mileage, but next day it ran very bad and was so weak and sputtering i feared i might be stranded. I went to wal-mart, bought some tin foil and removed the egr valve, packed the tube with foil and replaced it. On the drive home it settled down and even got oput of limp mode for a few minutes. It now runs smooth, it jsut gets poor mileage and has no spark advance. Every once in a while it gives me a few seconds of "normal" mode but as soon as I change anything from steady (give it gas, slow down a lot, etc) it goes back into limp home mode

My father bought this car for me on my birthday. I am 44 years old and he is getting along in years, I see it (and I'm sure he did) as a sort of last project for us. I really like the car, I am a big guy and it is incredibly roomy compared even to my old Mustang. I also think it's a sharp looker so I am prepared to spend some money on it (the dull factory red will get a topcoat of pearl white, I always wanted a hot pink car), but I absolutley refuse to pay $300 for an EGR valve and the research I have done indicates this model had other problems as well with spark modules and even the ECU and these are all ridiculously expensive - I can build my own ecu and ignition system for LESS than the OEM replacement parts, and if one of my modules fails I can repair it (not to mention programming it myself for performance/fuel economy, etc).

My question is: for those who have more experience than I with these models, does this look pretty much like the ECM just refusing to work "normally" with no proper egr control? I am an experienced electronic engineer with a background in detroit. I have even designed electrical test fixtures for GM and designed an engine controller. My plan is now to just replace the ECM with a megasquirt kit and program it myself.

The car is old enough I can get by in this state without that cats and egr valve. I would welcome some advice here, however, if it might be some simple sensor problem then I could at least get the car running normally and could drive it now before doing the ECM work, right now it runs smooth as a (weak) top but sounds like a lawnmower and drinks gasoline.


Thanks for reading my tome,
new beretta fanboi

[Blue Bowtie]

The '92 will be the older ECM (should be the old '727 ECM). Since you can reprogram, you should also be able to scan. Are there any persistent error codes?

There are a few common problems with that vintage MPFI engines:

1. The Multec injectors are susceptible to electrical failure (coil insulation breakdown). It may be helpful to check the injector resistances while the engine is fully warmed;
2. The O² sensors are the old, single wire variety and are usually good for about 30-40,000 miles before the signal starts to degrade;
3. The linear EGR valves used on them can "fail" from carbon and coking in the pintle and seat areas, and can frequently be removed and cleaned with success;
4. The DIS system uses a wasted spark (firing two plugs simultaneously) and spark plug gaps, condition, and plug wire integrity are critical. The coil pack itself can be susceptible to moisture incursion and accumulation under the mounting plate.

There are probably some others I'm overlooking, but those are the more common ones.

You can scan for error codes with a scanner or by grounding the diagnostic request line at the ALDL on your '92.