S5 T2 Mop/ecu ?

[Phoenix7]

Ok. So I'm working on a car for another forum member here that has a problem that is USUALLY easy to fix/diagnose. Its a 1991 T2 and when he brought it to me, you could drive around for a few minutes until it got really warmed up, boost or not about 15 minutes into driving it would toss a CEL and go into fixed timing/fixed fuel and make the car hesitate and basically become undriveable.

This problem is TYPICALLY a bad MOP. I tested the MOP according to the FSM "safety" margin which is 19 to 23 ohms. It failed. So, he had another one in the back that had a connector rewired to it from a running car and should have been in good condition - no such luck. I couldn't even get a reading on that one. I can only assume its probably because that connector had been cut/reconneced and over time has worked loose.

Anyway.. so I had a 3rd OMP from a JDM engine which tested out 22.8ohms across the board, so it was "good" but marginally. I went ahead and swapped it in to see if it would solve the problem. So after letting it sit overnight w/ the battery disconnected, I hook everything back up, warm her up and go down the road. Just as before... there goes the CEL and the fixed timing/fuel.

Get it back home, let it cool off and retest the MOP. Now I'm showing 24.2 to 24.8ohms...

???

My issue is what would make the MOP go out of spec that quickly?

I've heard that you should also replace the ECU when replacing the MOP due to failed resistors in the ECU. Is this true? Which resistors in the ECU go bad and how can I check them - I dont see this in the FSM.

I've swapped other MOPs before with no issues from the ECU.

Oh - and its still not throwing any codes.

Thoughts, suggestions? I'm going to retest the MOP once the car completely cools down...

If in fact its the ECU misbehaving, now it'll need an ECU and another good condition MOP...

Oh - and here are some pics in case the owner wants to see some surgery shots! The last shot isnt anything really - I just like having two awesome FCs in the garage

[WE3RX7]

Ok. So I'm working on a car for another forum member here that has a problem that is USUALLY easy to fix/diagnose. Its a 1991 T2 and when he brought it to me, you could drive around for a few minutes until it got really warmed up, boost or not about 15 minutes into driving it would toss a CEL and go into fixed timing/fixed fuel and make the car hesitate and basically become undriveable.

This problem is TYPICALLY a bad MOP. I tested the MOP according to the FSM "safety" margin which is 19 to 23 ohms. It failed. So, he had another one in the back that had a connector rewired to it from a running car and should have been in good condition - no such luck. I couldn't even get a reading on that one. I can only assume its probably because that connector had been cut/reconneced and over time has worked loose.

Anyway.. so I had a 3rd OMP from a JDM engine which tested out 22.8ohms across the board, so it was "good" but marginally. I went ahead and swapped it in to see if it would solve the problem. So after letting it sit overnight w/ the battery disconnected, I hook everything back up, warm her up and go down the road. Just as before... there goes the CEL and the fixed timing/fuel.

Get it back home, let it cool off and retest the MOP. Now I'm showing 24.2 to 24.8ohms...

???

My issue is what would make the MOP go out of spec that quickly?

I've heard that you should also replace the ECU when replacing the MOP due to failed resistors in the ECU. Is this true? Which resistors in the ECU go bad and how can I check them - I dont see this in the FSM.

I've swapped other MOPs before with no issues from the ECU.

Oh - and its still not throwing any codes.

Thoughts, suggestions? I'm going to retest the MOP once the car completely cools down...

If in fact its the ECU misbehaving, now it'll need an ECU and another good condition MOP...

Oh - and here are some pics in case the owner wants to see some surgery shots! The last shot isnt anything really - I just like having two awesome FCs in the garage