I have been monitoring this forum and have several related questions to help me
understand and diagnose my 1990 Turbo II.

Car History:

I'm the original owner of this car and have done all maintenance. The car is
completely stock with 75K miles. Car is only ocassionally driven, especially since
the following problems occured. Several years ago, this car started displaying a
MIL Check Engine light and going into "limp home" mode. However, no ECU codes
were displayed. In the past I have read and used the Error codes to diagnose a
bad TPS. I have been trying a multitude of tests and fixed a number of unrelated
things but no solution. About a year ago I did open up the ECU and inspect it for
possible problems. There was nothing noteable and the two boards looked OK.
Within the last two weeks I decided to look again at the ECU and replace the
electrolytic caps that were on the boards. When I openned the N370 ECU this time I noticed burn marks and a Toshiba MP4501 IC that destroyed itself and a 0.1power resistor. This component drives the MOP stepper motor.

Questions:

1) Does the fact that a known failure has occured (MOP or/and electrical driver is
bad) but no ECU Error codes are displayed - mean that part of the ECU is bad? Like memory failure or something else?

2) Do all S5 ECU's have the same electrical driver for the MOP?

3) What caused what to fail first - the MOP or ECU?

4) Checking the MOP stepper motor resistance readings according to the FSM says there is no problem. I got 25.8, 22.8, 19.0 and 23.1 ohms for each of the windings from B+ terminals. However, when I measure the across both windings I get 45.4 ohms=OK and 10.1 ohms=Not OK? Does this indicate an internal short in the stepper motor?

Any help sorting through this or prior experience is welcome. Thanks.

 

Hard to say there is not much out there on testing the electrical omp. when you mention electrical most tend to keep this info secret or it feels like they do. I would check the wireing for shorts to b+ and ground back to the pins on the ecu plug as well before repairing the ecu driver. I will measure my omp resistance and compare to your data tomarrow. check your stepper windings to the case of the motor as well if any are shorted to the motor case this would burn a driver.
as far as the electrolytics in the ecu they appear to be of good quality and not bad like other newer electronic equipment. I have herd that an open solder connection in this circut can stress the driver IC. but there is no monitoring for the check engine light on the lines to the stepper that i know of its just an output ic driveing the stepper motor.
Also not much info on the amount of oil flow or how to test for proper operation that i could find. I would sugest premix the fuel while it is down to avoid any mechanical failure due to non lubercation.

 

OMP kills ECU, then ECU may or may not report the fault but it will go into limp mode. Since I dont know of anyone who repairs ecu's, most people replace. This may be an issue with your rare n370, so if you can repair then that is great. All s5's use the same OMP, so I dont see why all s5 ecu's would not use the same driver. Both NA and turbo ecu's are basically identical with differences in programming for timing and fuel injection, and the turbo monitors knock and operates a boost solenoid, while the NA operates 6pi and vdi valves.

The best thing to do is get an OMP from a known running engine (no codes, no limp mode) and then repair/replace the ecu. When people come to me with this issue, I recommend getting both at the same time, from the same car if possible.

You might *try* an n374 jspec turbo ecu as well. Some people report that these ecu's will not work in their car, while others (including myself) have done the swap without issues. You can get these for 50 bucks or so if you look around a while, and so it might be worth a try.

 

Checking for shorts between the windings and the case or ground of the MOP occured to me too. I'll be doing that today. I am wondering whether I have done damage to the engine internals by driving without the MOP working. My understanding of the S5 MOP operation is that it regulates the flow of engine oil to the four injectors. It does not do the actual pumping, that is done by the engine oil pump.

So, if the MOP stepper motor did fail, doesn't some minimum oil amount get to the injectors/engine?

Is it possible to replace the stepper motor on the MOP while on the engine? This may prevent damaging the clear injector tubing.

Thanks for the input!

 

With regard to my replacing all 5 electrolytic caps on one of the ECU boards. I agree that after removing and a careful visual inspection, they looked OK. No leaking or bursting of their cases. I measured the capacitance of the 10 uF and it was good. I could not measure the others they were larger than the meter range that I had available. I did replace them with new caps.

 

BTW because I'm concerned about engine lubrication without the MOP, I have started to premix some Havoline TC-3w two cycle oil with the gas. About 1/2 oz oil to1 gal gas ratio for now.

 

Running w/o OMP injection for a short while will not affect engine health, other than perhaps a slight temporary drop in compression due to less of a coating of oil on the housing walls. Actual seal wear in the short term is negligible. Now, over a long term, this would definitely be a concern.

You can easily remove the OMP from the engine while in the car, and not damage the OMP lines. Gently bend all 4 of them back out of the way.

 

The reason I'm asking whether the stepper motor can be replaced with the MOP on the engine is I'm afraid the tubing will be brittle after 17 years and break if moved. (Other vaccuum hoses I have replaced fractured when moved.) I want to disassmble the least to prevent damaging fragile old parts.

I have seen some MOP dissection photos with the stepper motor seperated from the MOP assembly. I am unclear as to whether there may be clearance in the engine compartment to just replace the stepper motor/position sensor.

 

I can't provide much technical support, but here's my experience. I did a JDM TII swap into my vert. Bought an N370 ECU and from the get-go it gave me phantom check engine code for my MOP. It would never go into limp mode. The MOP tested ok but I replaced it anyway with a known good one from my N/A engine and got the same CEL. I just recently replaced the ECU with a different N370 and have been driving it for just over 2 weeks with no CEL for the MOP.

Not much help figuring yours out, I know. But , I'll toss this thread into my subscriptions. I'd like to find out if the ECUs can be repaired. If it would help I can crack open my bad N370 and my N352 ECU and get some digital pics so you can compare the boards. I wouldn't be able to get those till this weekend though.

 

200:1 is probably not a very safe mix ratio if your OMP has failed and you are unsure of its operation... granted, nothing bad will happen in the next 50miles or so.. but... why risk it? Just run 150:1 or better.. 100:1 is what most premix people run. If it were me, I would just throw 100:1 in for an added buffer zone. You might get a small amount of visible oil smoke, but.... piece of mind is worth it IMO.

 

Reason I choose the 250:1 (gas:oil) ratio was that from what I have concluded the MOP just regulates the oil flow to the injector ports. So even if it doesn't vary the way the ECU wants it to there still should be some oil flow through it coming from the engine oil pump. That may be why the ECU goes into "limp home" mode when it determines the MOP/sensor is bad. The amount of oil that flows into the injector ports is a very small amount.

Has anyone dissected a MOP completely to understand how it works with the attached stepper motor and sensor? Are there some detailed photos of the components?

 

Its the "may be" and "should be"'s that I hate to rely on.

 

It would be very difficult to try and disassemble the OMP on the engine. It is only 3 bolts holding it on. If you are gentle you should not break the OMP lines, just be careful of twisting them at the fitting ends themselves. The lines are usually fairly pliable toward the center, so bend them there. I routinely disassemble and reassemble engines with the original OMP lines, many with a lot more years and miles than yours.

I have taken some OMPs apart as well. There is even discussion on rx8club as to possibly modifying the OMP for a higher injection rate.

 

I did just verify the individual MOP stepper motor winding resistances again and checked that there are no shorts to ground. After thinking about it some more, I'm sure that there must be an internal short within the motor itself. This would account for the lower resistance value when comparing the one pair of winding in series to the other series pair (45.4 vs 10.1 ohms).

Has anyone ever measured a good MOP and recorded all the terminal resistances - not just the ones in the FSM?

 

I have measured tens of OMPs and always get 21-24 ohms on all 4 tests.

 

With stepper unpluged C TO A = 21.5
C TO E = 21.5
D TO B = 21.5
D TO F = 21.5
A TO E = 43.0
B TO F = 43.0 ALL IN OHMS APPROX READING NO MORE THAN 2 OHMS ERROR

pins C and D tie in the car harness to +12 volts. however when testing the motor out of car or unpluged the motor pins C and D are isolated and should be no connection between C and D. Only when pluged to the car harness should you read connection on C and D.
From the resistance check you did you have a bad stepper. The stepper IC is aval on the net and I have changed them before and they worked along with the supply resistor which opens to prevent the whole ecu from shutting down due to a blown fuse. replace the resistor with the same rateing in wattage.
Also you can replace the ecu if you like but if you can handle the repair go for it. I am an electronics engineer this is the reason I have done most of my on electrical fixes and have had lots of experences in the ecu itself. Im a little rusty on mechanical knoledge as I learn it as I experence it.
As i have seen in the past the stepper fails a winding opens or shorts, Shorts most of the time and will take out the ecu driver if the stepper windings short.
if you get lucky the stepper opens which is rare and then the ecu dosent get hurt.

 

To be more clear, the measurement that I believe is bad for my MOP is between SM3 and SM1 or SM4 and SM2 on the EM-21 connector. This not a measurement that the FSM describes, which is between +B1 and SM3 or +B1 and SM1 or +B2 and SM4 or +B2 and SM2. These range from 16-31 ohms in FSM. The resistnance measurement that I took is across both coils that are in series. Therefore, the value should be the addition of the two FSM measurements for respective pairs of windings. It seems the value across both winding (coils) should be 23 + 23 = 46 ohms. One of my pairs is 10.1 ohms. This means something is reducing the resistance - the internal short.

 

Yes you have found the shorted winding. thats what we wanted to see.

 

Just read your measurement data post, after I clearified what I thought was failing with my MOP stepper motor. Your data has confirmed, that I do have an internal short. This would have prevented or made it difficult for the ECU to move the stepper where it should have to be during operation. Most likely as you stated also finally caused my ECU driver IC to fail.

Where did you get the Toshiba MP4501 driver IC? The power resistor is 0.1 ohms, but what wattage?

My resistor is open and black. From inspecting the board, it looks like there is the same resistor near the MP4501. Possibly for the other winding pair and performing a current sensing function for the microprocessor. Just a guess.

I have some electrical engineering background also.

 

there are 2 circuts used in the ic one side has failed with the low resistance which the resistor is to protect the traces from burning and also the ecu fuse from blowing leaving the car stranded. I used 1/2 watt. The ic when i got them was mostly from scrap ecu's but some came from digikey online. also the data sheet pdf is online as well. The IC is a basic transistor pair type driver circuts.
If using a scrap ecu if the resistors are burned the omp circut has failed.

 

I just checked DigiKey and have previously checked other electrical suppliers, however the MP4501 must have gone obsolete years ago. I guess I'm going to look for good S5 ECU's and transfer the parts.

 

http://www.summaelectronics.com/cata...3_products.htm

 

I have checked out Summa Electronics a part is listed but no description nor spec sheet. The Toshiba MP4501 is a High Power Switching Application for Pulse Motor Drive with Inductive Load in a SIP 12 pin metal tab power package. It contains 4 Darlington transistors with flyback diodes.

Any other source suggestions?

Secondary problem, if I can manage to locate and fix the MOP driver section in my N370 ECU, I am still wondering why I can not get any ECU Error Codes prior to the MOP/driver failure?

What is an easy test to do to ensure that the ECU can store Error Codes? Unplug a sensor or somthing to test the ECU memory.

 

Ok just checked with dalbani.com they have the toshiba ic in stock $ 3.65 each

I do know if you unplug the tps it will give you a check engine light and the tps code

 

Just unplug something like the boost/pressure sensor, air intake sensor, TPS etc.