Intermitten throttle/ignition cut?

[Alex Mc]

Hey guys,

The car is an '85 but has the 1.3 Motronic on a 2.8L M20 that's converted to 'i', etc.. it has high compression, dual-patter Schrick cam, our chip in a 173 ECU.. when you're driving it, every once in a while the car bucks when the ignition just cuts out randomly. It feels like ignition.. here's what i've replaced/tested:

-Ignition Relay
-Rotor
-Cap
-ECU
-Coil
-Plugs (appeared normal)

Do you think the plug wires could be at fault? TPS?

Any ideas or experience with similar symptoms?

Thanks in advance..

[bimmerphile]

Alex,

Someone else posted about a similar problem no more than 2 weeks ago. I can't remember what the culprit was though.

Hopefully they'll reply.

[nando]

that thread was a little different.. it wasn't really a buck, but more like a flash power loss. I don't think the culprit was ever nailed down, but one common thing between cars showing the symptoms was very cold weather (far below freezing). Somebody mentioned the O2 sensor, which I was replacing anyway. my car hasn't done it since, but it hasn't been really cold either.

[rwh11385]

Re: Intermitten throttle/ignition cut?

Any ideas or experience with similar symptoms?

I don't know if it has anything to do with it, but occasionaly I'd be driven along the the car would almost shut off real fast. The lights all blink for an instant and the revs drop. I also had a 173 ECU. Only happened a few times tho.

[Alex Mc]

Well the more aggressive "bucking" only happened as a result of low road speed combined with a real short 4.10 LSD and being in 1st or 2nd gear.

It has to be an ignition cut, because just today he had it backfire on him after it happened again.. which means that the ignition cut out while the fuel was still firing, so when the ignition comes back online it burns off that excess and causes a backfire. So, now i'm certain its ignition, but still looking for a solution..

Anyone have a link to the other thread?

[iXer]

I've answered this question back in the old e30sport forum, in my case I had the same symptoms: The car could suddenly just die, as if the ignition or fuel was cut. Every lamp in the instrument panel would go out, power was lost. Turning off the ignition and then on and it would start up like normal. Sometimes it would just stumble, just for a fraction of a second.

For me it was clearly an electrical problem, I had relay problems. And I though I had to replace them but..

The solution for me was to clean the surfaces of the main relay and fuel pump relay. On the iX and most other 325 cars, those two relays are found beneath a plastic shield in front of the left shock tower. Turning on the engine and lightly tapping the plastic shield would kill the engine or make it stumble, that was how bad it was in the end.

[Brew]

I've got a 173 ecu also....

http://www.r3vlimited.com/phpBB2/viewtopic.php?t=3011

The problem hasn't happened since, but I definitely would like to address it. It is definitely associated with heavy load on the engine...either hard acceleration or high speed highway cruising.

[Alex Mc]

I've answered this question back in the old e30sport forum, in my case I had the same symptoms: The car could suddenly just die, as if the ignition or fuel was cut. Every lamp in the instrument panel would go out, power was lost. Turning off the ignition and then on and it would start up like normal. Sometimes it would just stumble, just for a fraction of a second.

For me it was clearly an electrical problem, I had relay problems. And I though I had to replace them but..

The solution for me was to clean the surfaces of the main relay and fuel pump relay. On the iX and most other 325 cars, those two relays are found beneath a plastic shield in front of the left shock tower. Turning on the engine and lightly tapping the plastic shield would kill the engine or make it stumble, that was how bad it was in the end.

This is not the case with this car.. it is clearly an ignition problem as the problem with a backfire i described avoce illustrates. Im thinking Speed Ref Sensor and maybe AFM?

alex

[James Crivellone]

does the tach act up? if thats it then the speed ref is to blame imho.


if its not, check the Coolant Temp Sensor, TPS and AFM

on my car it was the AFM acting up, pop the cover, if its all corroded replace it

[65Matt]

Alex,

I had the same problem and it was the main relay. It would cut out randomly. I replaced the relay and sprayed contact cleaner to clean the connections. Have you tried the test he described?

Turning on the engine and lightly tapping the plastic shield would kill the engine or make it stumble

[UNHCLL]

Check the spark plug wires, they could be crossfiring if they have worn through.

[Alex Mc]

I'm basically 100% certain its the air-flow meter.. going to check it out tomorrow, i'll update accordingly.

[Alex Mc]

Well today we cleaned out the track on the AFM and unfortunately the problem is persisting. I suppose we will throw a new Speed Ref. Sensor in there to see what that does for us.. and if that makes no difference (i'm still not clear on how it will) then maybe the AFM is bad?

Does the circuitry poop out on these trap-door AFM's? I know if i had an oscilloscope I could check the output through the throttle-angle sweep, but i don't.. is there a way to test them with a multi-meter perhaps? If anyone has any ideas i'd be very appreciative.. this one is driving me nuts! We've tested so much!

thanks in advance..
alex

[James Crivellone]

Well today we cleaned out the track on the AFM and unfortunately the problem is persisting. I suppose we will throw a new Speed Ref. Sensor in there to see what that does for us.. and if that makes no difference (i'm still not clear on how it will) then maybe the AFM is bad?

Does the circuitry poop out on these trap-door AFM's? I know if i had an oscilloscope I could check the output through the throttle-angle sweep, but i don't.. is there a way to test them with a multi-meter perhaps? If anyone has any ideas i'd be very appreciative.. this one is driving me nuts! We've tested so much!

thanks in advance..
alex

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i tested mine with a meter, and it was ok, however after I popped the cover off and noticed how bad it was I decided to replace it.

the issue is recreating the problem on the bench