violently random bucking confused...

[SHOlover1]

i have a 91 mtx that had been sitting for three years we just got running again, titled and inspected. We were driving back home from where it was sitting for the week. Just running down the interstate bout 2 3/4k and it randomly just jerks a little and the eatc flashes on and off. We thought ok just a fluke and it didnt really happen again until today.

i was just getting on it a bit and i get to about 4 1/2k in 2nd starts jerking a bucking like the motor was trying to lock or die or something. I was thinking either cid or cps possibly... im running on guesses and suggestions cause i can not check codes until i can replace the cel in the dash due to previous owners took it out and i dont have a scanner. ca yall tell me what yall think...

 

[raff18]

id look at these
dis
coil pack
plugs , wires
cps
and deeper if still nothing

 

[eLindemann]

Also try cleaning out the idle air bypass valve. An old tank of gas gunked up mine, and since yours has been sitting for 3 years you might wanna look into it.

 

[jayhoyt28]

Also try cleaning out the idle air bypass valve. An old tank of gas gunked up mine, and since yours has been sitting for 3 years you might wanna look into it.

Same here. Old gas did it in. And cleaning it didnt solve it. I had to replace it.

 

[projectSHO89]

Your symptom is typical of a bad CID (cam) sensor or intermittent loss of the CID signal.

Unplug the sensor and test drive it. Disregard the resulting CEL and be prepared for several starting attempts whenever you wish to start it. If the random bucking goes away with the sensor disconnected, then the sensor is probably bad or has a bad connection.

 

[rubydist]

The most likely candidate, in my experience, is a bad ground.

The eatc flashing on and off means that it is seeing voltage less than 11V. Good chance that is due to an intermittent ground. Depending on which ground it is, that can also mess up the dis or the crank sensor, which would lead to the engine cutting out and in again.

 

[Phoenix]

Since its violent jerks , I think its the crank sensor , I had this happened to me a couple times.

If ever its not that , go with the cam sensor.

 

[ViPER1313]

Have you checked for codes stored in the computer?

This is exactly what my car did when the cam sensor died, but it also set a fault code in my computer immediately (bucked 2 or 3x driving over a 150mile trip home, got home, pulled the codes and got the one for a bad cam sensor signal.)

 

[SHOlover1]

Your symptom is typical of a bad CID (cam) sensor or intermittent loss of the CID signal.

Unplug the sensor and test drive it. Disregard the resulting CEL and be prepared for several starting attempts whenever you wish to start it. If the random bucking goes away with the sensor disconnected, then the sensor is probably bad or has a bad connection.

unfortunately when i unplug it the motor dies the first time it ran better but wouldn't start back up after it was shut off i do need to clean the iac or replace i cant check the codes until i can get a obd1 scanner or i replace the check engine light in the instrument cluster

 

[91PDXmocha]

had this problem. Id guess bad ground, DIS , or crank sensor.

 

[ViPER1313]

unfortunately when i unplug it the motor dies the first time it ran better but wouldn't start back up after it was shut off i do need to clean the iac or replace i cant check the codes until i can get a obd1 scanner or i replace the check engine light in the instrument cluster

Yes, you can check the codes even with a burnt out CEL - you can hook up any sort of light bulb or a multimeter in DC voltage mode between the positive terminal of the battery and the self test out pin as explained here:

http://www.shotimes.com/php-bin/modules.php?op=modload&name=News&file=article&mode=thread&order=0&thold=0&sid=83

The light or multimeter will blink / sweep the codes for you.

 

[Rubix]

Just open the dash and swap the CEL bulb with another bulb, it'll take less than 5 minutes. Or go with the method Viper just described.

I don't think you're going to get anywhere with this until you get codes, too many things it could be.

 

[SHOlover1]

Just open the dash and swap the CEL bulb with another bulb, it'll take less than 5 minutes. Or go with the method Viper just described.

I don't think you're going to get anywhere with this until you get codes, too many things it could be.

I'm gonna go with viper, but for reference what do i need to do to replace that CEL. Does the whole dash need to come apart

BTW She gave out on me on the way back from Richmond today. With the tach crusing at 60 at between 2 to 3k and randomly bucking and tach jumping crazy from 2k to 0 to 8 1/2. It just did that back and forth all the way back, untill it said no more and had to have it towed...

 

[rubydist]

Crank sensor is a pretty likely candidate for that issue.

 

[ViPER1313]

I thought that the tach was fed purely by the cam sensor, not the crank sensor.....

Just pull the codes - they should indicate cam or crank sensor.

Some people claim that the car will still run with a bad cam sensor - I have never been able to get the car started and keep it running with the cam sensor unplugged.

 

[SHOtime2511]

I thought that the tach was fed purely by the cam sensor, not the crank sensor......

you would be correct.
I think people say crank sensor like they say crank canser these days.

Again check the CAM sensor first then check some grounds including the engine ground on the rear passanger side on the intake manifold and lastly it could be the IAC.

 

[SHOlover1]

you would be correct.
I think people say crank sensor like they say crank canser these days.

Again check the CAM sensor first then check some grounds including the engine ground on the rear passanger side on the intake manifold and lastly it could be the IAC.

It was the cam sensor seal had been leaking after been replaced in 2007 and parked for 3 years. It would make sense, but i haven't drove it but 20 miles today since i replaced it, but she was warmed up the tach didn't jump and the car hasn't bucked still dies but i still need to clean the iac or replace it.

 

[projectSHO89]

I thought that the tach was fed purely by the cam sensor, not the crank sensor.....

Just pull the codes - they should indicate cam or crank sensor.

Some people claim that the car will still run with a bad cam sensor - I have never been able to get the car started and keep it running with the cam sensor unplugged.

The tach is fed by a composite of the CID/CMP signal, the CPS/CKP signal, and the three coil signals. All are required for the IDM signal.

I ran my 89 for several weeks way back with the CID sensor unplugged. It can be done. It often took several attempts to start, but once it was running, the engine ran normally.

 

[SHOlover1]

It was the cam sensor seal had been leaking after been replaced in 2007 and parked for 3 years. It would make sense, but i haven't drove it but 20 miles today since i replaced it, but she was warmed up the tach didn't jump and the car hasn't bucked still dies but i still need to clean the iac or replace it.

Strike that.......

If its not one thing it another right?
Coming home tonight. I lost the throttle and the motor died then coasted up the hill a bit popped the clutch then heard a "whap"... with a smell of burnt rubber(sound like a belt snapping). Then continued coasting to the top of the hill turned off then into the post office. From there i checked the 2 belts but they were there so i figure my fears were bout to come true.
The timing belt either slipped or snapped cant check it till tommorow before work but it will crank fine but no start... i almost am about to think this 91 is gonna be more of a money pit then my 92

 

[SHOtime2511]

It was the cam sensor seal had been leaking after been replaced in 2007 and parked for 3 years. It would make sense, but i haven't drove it but 20 miles today since i replaced it, but she was warmed up the tach didn't jump and the car hasn't bucked still dies but i still need to clean the iac or replace it.

The cam sensor is magnetic.
If it does happen to get oil in there it won't effect anything.