Thread: 3800 n/a need some help

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.

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

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.

the pre OBD II was next to useless. Any one part can place it in limp mode.


Couple more qustions

1. If the transmission was in neutral would it do the same. Rev it up ad see
2. Part of the shaking has me looking at your transmission, automatic with modulater?
if you were invovled in an accident weights could have fallen off
3. What does the trouble codes say, did you red the blink or use a scan tool
4. I am leaning at the transmission. Lets rule it out.
1. What does the fluid look like
2. Filter ever been changed
3. Is there modulater cable, make sure it works with your throttle pedle.
4. Look at your drive shaft and see if any thing look diffent.

What you gotta do is start canceling things that do work propelry from those that don't. Sounds and vibrations can come from everywhere. Shaking of your engine while running in gear or in neurtal tell differnet stories.

happy hunting

mongo

I am also not forgeting that your torque converter could also have a frozen stator, that would make it shake rattle and stop rolling. hmmmm

Originally Posted by mongo

the pre OBD II was next to useless. Any one part can place it in limp mode.


Couple more qustions

1. If the transmission was in neutral would it do the same. Rev it up ad see
if your in N and rev it, it goes to around 4,500 to 5k i think and drops off and goes back up almost like a rev limiter but it gives the same miss fires

2. Part of the shaking has me looking at your transmission, automatic with modulater? it is a automatic not sure what modulater your talking about
if you were invovled in an accident weights could have fallen off
the car has never been crashed, but after this all started i had a drunk roll in to the back of it sitting at a red light but it didnt even put a scratch on it

3. What does the trouble codes say, did you red the blink or use a scan tool
scan tool and you can monitor the cylinders and you see the miss fire pop up.

4. I am leaning at the transmission. Lets rule it out.
1. What does the fluid look like
not sure but i dont think the tranny would give you 3 or 4 different cylinders miss firing
but we haven't changed the fluid in it ever.

2. Filter ever been changed
no
3. Is there modulater cable, make sure it works with your throttle pedle.
where would it be connected on the transmission?
4. Look at your drive shaft and see if any thing look diffent.

What you gotta do is start canceling things that do work propelry from those that don't. Sounds and vibrations can come from everywhere. Shaking of your engine while running in gear or in neurtal tell differnet stories.

happy hunting

mongo

we swapped out the icm that the coils sit on with a brand new 100$ i found on the web and nothing changed really. still clueless.