S5 T2 Mop/ecu ?

WE3RX7 · 10-13-2008, 12:50 PM

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

Phoenix7 · 10-14-2008, 02:47 PM

well, I've heard that a bad OMP can take out the ECU so if your ECU was damamged it might be damaging the newer OMP?

Any luck yet?

WE3RX7 · 10-14-2008, 11:00 PM

I cracked the ECU open tonight, but it "looks" ok.

The toshiba MOP driver is normal and the .1ohm resistor that goes along with it is ok, I assume. Its slightly browner in color than the other blue resistors, but there is one other resistor in a separate row the same color, so I'm not sure if thats the normal color they are supposed to be.

I've got another S5 ECU (NA) here as well that I'm going to crack open to compare though.

I'm a little stumped as really this is the only thing that makes sense, its either the MOP or the ECU. I'm retesting the MOP according to a more "strict" guildeline to see what it comes out as. I know its got to be something simple.

If need be, I'll keep digging until I find a "perfect" OMP and ECU though. A real solution would be to upgrade to an RTek 1.0, which ditches the LIMP mode and then run premix for the time being. At least then the car could be enjoyed....

WE3RX7 · 10-15-2008, 03:43 PM

New plan - RTek 1.5 for the S5. No more LIMP mode. I personally feel this is the way it should be. You can ditch the stupid problematic EMOP and either run premix, or swap to an S4 TB and Mechanical MOP.

Not to mention, this car has full 3" exhaust, so the RTek will help with adding a little security w/ the built in FCD and better timing adjustments over 9psi (which with this exhaust, the car should support 10psi all day). Should net a decent HP gain for not a lot of doe and it'll be seemingly factory without the factory headaches.

10-13-2008, 12:50 PM	#1
WE3RX7 RCC Addict Join Date: Feb 2008 Location: VA iTrader: (1) Posts: 1,812 Rep Power: 18	S5 T2 Mop/ecu ? 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 Last edited by WE3RX7; 02-04-2009 at 11:47 PM..

10-14-2008, 11:00 PM	#3
WE3RX7 RCC Addict Join Date: Feb 2008 Location: VA iTrader: (1) Posts: 1,812 Rep Power: 18	I cracked the ECU open tonight, but it "looks" ok. The toshiba MOP driver is normal and the .1ohm resistor that goes along with it is ok, I assume. Its slightly browner in color than the other blue resistors, but there is one other resistor in a separate row the same color, so I'm not sure if thats the normal color they are supposed to be. I've got another S5 ECU (NA) here as well that I'm going to crack open to compare though. I'm a little stumped as really this is the only thing that makes sense, its either the MOP or the ECU. I'm retesting the MOP according to a more "strict" guildeline to see what it comes out as. I know its got to be something simple. If need be, I'll keep digging until I find a "perfect" OMP and ECU though. A real solution would be to upgrade to an RTek 1.0, which ditches the LIMP mode and then run premix for the time being. At least then the car could be enjoyed....

10-15-2008, 03:43 PM	#4
WE3RX7 RCC Addict Join Date: Feb 2008 Location: VA iTrader: (1) Posts: 1,812 Rep Power: 18	New plan - RTek 1.5 for the S5. No more LIMP mode. I personally feel this is the way it should be. You can ditch the stupid problematic EMOP and either run premix, or swap to an S4 TB and Mechanical MOP. Not to mention, this car has full 3" exhaust, so the RTek will help with adding a little security w/ the built in FCD and better timing adjustments over 9psi (which with this exhaust, the car should support 10psi all day). Should net a decent HP gain for not a lot of doe and it'll be seemingly factory without the factory headaches.