k i know its a little off topic but it looks like you guys have a nice and knowledgeable community.

i have a 95 trasport van with the opt motor (3800)its got 98,000 miles on it now, and has started to get a slight miss in it. i would say it started last winter/spring and is now getting worse. there is kind of a sweet spot when you accelerate were it feels it has all the power it use to. but if you try to drive away from a light (like the bigger motor would ) it sorta just stumbles and falls on its face. also it no longer revs past 4,200 rpm, it drops right down to 3,500 and goes back to 4,200. the redline is at 6K.

the other thing i have noticed is when your driving along at 40 mph or so and put your foot on the pedal to speed up to lets say 45 the rpm start to clime, they get to 2,500 and drop to 2,000. when i say drop its almost like the motor turns off it goes down so fast. once and a while it will shake a little when it does this.

we have a actron scaner and it shows a cyl 1 and 4 (same coil pack) miss fire at idle and when you rev it, and cyl 3 at idle miss fires. other then that it shows a code for a miss fire signal and nothing else.

if you need to know any numbers from the scanner about the motor just ask and i will get them and post

before this happened we were joking around about doing a burn out contest in this van now were joking about burning this van up.

I'd venture a guess of either bad ICM or bad coils.

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2004 Impala LS - got some mods
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k we have replaced 2 of the coils 5,2 1,4 so far so it looks like time to grab a icm from the junk yard and see if the problem goes away.

is there any check you can do with a multimeter for resistance or any thing to tell for sure? the coils have a resistance that goes out of a range when they go bad is there any thing like that for the icm?

had a 2001 4.3L chevy eat its self (dexcool ate the head gaskets and filled the oil pan) so we haven't really tor in to this motor yet but the 4.3L is back and running and broke-in so its time to try a few things to get rid of this miss

go to where you can flush out the fuel injection system. change all filters and then take apart your TPS and clean it as well. Now that you eng is cold pull your plugs and read them. If they are good get your Ohm meter out and check your wires. Then get a node and check your Injectors. Once you can claim she is clean you will have only a few places left to check. Some which can be costly. But you will know what it is not.

we pulled a icm off a car that was said to use the same icm part but the pins on it are different is there any reason it would be missing a one of the connectors? its the same plug from the same motor just its missing one of the pins. would there be a problem just plugging it in and trying it....

o and one other thing that has started now. on the dash there is a switch for tc so you can turn it off (very useful ) but with the motor running the way it is the light is just off now cant turn it on/off. with the miss in the motor it doesn't have enough power to spin the tires like it use to so you can't tell if its just the light is burned out or if it really is off. is it possible that the whole ecm is just taking a slow drawn out dump on me? lol

I agree with Mongo, start with the simple stuff. I have been guilty of assuming the simple things are okay but, in the end, they turn out to be the problem.

A clogged fuel filter could cause some of what you are experiencing but doesn't explain everything.

we have cleaned the tps cleaned the k&n air filter and i am pretty sure we changed the fuel filter last year. the tc light being out makes me thinks something bigger is the problem. we have a scanner for it and it says that the 1,3 and 2,5 miss fire when it gets this shake in it. that would make me think its a ign problem not a fuel problem b/c 2 of the cylinders miss fire. any other guesses really don't wanta spend a lot of money on this van its 13 years old and the under side isn't the best looking some of the supports are rusted out and the dealer broke 2 of the bars that mount parts of the body to the center of the car when they put it on the lift a few months ago to look at something else

its only going to be maybe 1 or 2 more winters and its going to the trash just want to make it run a little better till then

please describe this 'shake', you have my attention. A miss fire on your reader could be caused by many things. Because it is showing up on most of your engine. How far can you go back t the original reason you started playing. What was the reason, fuel?? What is an icm, did you mean ecm or ecu??

you mention the year is 95, is it OBD II or an earlier version, this is very important

mongo

its a odb not a odb II. the shake.... k if your driving along in over drive say doing 40-45 miles an hour and try to speed up to 50 mph, the rpm start to go up and they get to like 2,500 and drop back down to 2,000 and it starts shaking front to back (i think its b/c its fwd so the motor shaking would shake the car like it does) if you hit the gas harder and have it down shift it will down shift and drive away better but still not with the power it use to have before this started. icm is the integrated control module. there are 3 coils on it, 2 spark plugs for each coil. we got a few coils from the junk yard (they were hard to find a lot of 3800's where missing them) and it didn't effect the problem.

is there a fail mode in the icm that is kinda like a "get you home" mode where it cant control the spark for the advance that you would want for a motor under a load? but it would just miss fire due to the spark being out of time but would work at higher rpms better?

we had the tps fail and was told that there is a get you home type of setting in the ecm that just lets the motor run but it loses a lot of its power and wont go over 3,000 rpm.

o and in 1st gear you can still hit the red line when it shifts but when there is a bigger load on the motor it craps out.

o here is the icm so you can see a pic of them http://www.rockauto.com/catalog/x,ca...,parttype,7172
the car looks like a million bucks just runs like a piece of trash now. if any thing it started last winter if that helps.