1991 Storm ECM

We have a high mileage 91 Storm with SOHC and Auto Trans. Last summer (05) it developed a nasty hesitation off the line when the outside temp began to run in the 85-90 degree range. I did some troubleshooting and part replacement, sensors, didn't use it much. In Sept the temp went down and the Storm got back to stormin around.

Now here comes the hot weather again and here we go again. This time I checked a little further. As a sensor scan tool (the type that monitors them in real time) for these beasties is too expensive I checked the sensors individually again. No codes being set either. Sensors seem ok.

I may, though, have found the problem this time. The ecm does flash code 12 but no additional codes. I can disconnect nearly every device connected to it and the beast runs without lighting its check engine light. The only exception seems to be the throttle position sensor.

The ECM in these cars is flashable. I am thinking that the unit is acting up. Reason, the idea that you can disconnect all that stuff without it setting any codes or lighting its little dashboard light. That would seem to me to be abnormal. You can even pull the connector for the O2 sensor and the car doesn't react.

As a result I am thinking of either getting the existing computer flashed or ordering another one that is preflashed. I think Kem sells them all ready to go matching the cars vin number.

Anyone seen this one before???

One other thing I am concerned about is that although the computer is bad it also may involve non ecm connected devices such as the evap cannister purge or fuel pressure or ?????

Thanks all

Fuel pressure is mechanical, Evap purge is primative as four sided wheel

Thanks G Rod.

I never really did get that all cleared up. As usual, the temp went down and the car is running almost right. There is only the most minor intermittant sign of a hesitation at this point. As the temp goes really down it will go away.

I also tried another ecm. The cars gas mileage, always not too good for something as small as it is, has run as much as 8-10 mpg better than it was. Everything else remained the same. But, what the heck, it's paying for itself in saved fuel.

The fuel pressure I did mean to check but my thinking has been running that it would be worse when it's cold if the pressure was low. Instead it runs better. But it should be checked.

The ecm is still also puzzling. I can still disconnect a pile of its sensors without generating a check engine light. Wierd! Checking the wiring harness is probably in order. The new and old ecm both seem to feel a little warm when the engine is running. I don't have clue #1 if that's normal.

Anyway, the day, the minute, the second I ever get back to work I'll replace my entire rolling junkyard with new vehicles. End of my Stormin problems at that point. :) I am getting old and dealing with these types of things has gotten old a long time ago. As a hobby its fun. As a necessity it really smells evil.

Thanks again.

Ted

i would definatly check your wiring harness, but also have you checked the airflow sensor? you could also try another ecm, I picked one up from a junkyard for sixty bucks, and returned it when I found it wasnt my prob.

i would definatly check your wiring harness, but also have you checked the airflow sensor? you could also try another ecm, I picked one up from a junkyard for sixty bucks, and returned it when I found it wasnt my prob.

Thanks much toolfan-

The car has actually been running mostly ok as the weather has been cold. It doesn't start the hesitation until it gets warm out. I think as it approaches sixty degrees it starts. As it gets hotter it gets worse.

I did actually put in a reconditioned ECM last summer. It got, I think, slightly better. On the other hand the gas mileage was always too low for a car that weighs little more than a lawn tractor. As soon as I put in the new ECM the mileage increased substantially.

The ECM does seem to get a little warmer than I would have expected but that might be normal. I have no experience with that. If its not normal it could be an abnormal load on it.

I thought I replaced the IAT sensor and nearly everything else but I am going to try a new one anyway as I am not really sure. It tests ok but who knows.

My suspicion is still the wiring. I never heard of a car where you can disconnect nearly every sensor and the ECM doesn't react by turning on the check engine light.

In any case the poor ole beasty is going to go to a new home soon. We've been using it as a station car but it is really nasty looking. Maco wants about a grand to doctor it up. It has a little rust and an ample supply of dents that came with it. I originally bought it several (5??) years ago as a fill in car when something else died. Rentals were rediculous to use. Somehow it stuck around. I even fixed a blown head gasket on the thing. Don't know why. I guess I am just stubborn.

I would like to get the hesitation out of it before trying to sell it. It would be easier and maybe I should have a little pity on the kid, gotta be at this point, that buys it. I just hate standing on my head with a vom to try to check that harness.

Thanks :)

Ted