tiamog

hey i'm new at this but i need help bad.! i had my 91 gxl diagnosed cause the check engine light was on and it came back that it was either my oil metering pump, short in wiring harness, trailing coil going out or ecu failure. here's the thing, if i start my car and do not drive off the light will not come on but as soon as i start driving the light will come on and my car starts running real rough. the dealership said that they checked my coil and it was fine so can anyone tell me what would be the easiest way to find out what the hell is going on? this is my daily driver.

RX7 allnight

if OMP is bad or ecu doesnt get a nice reading than it goes into LIMP mode and runs rough

magus2222

iTrader: (22)

why the hell did you go to a stealership? i have yet to find anyone, even the people that work at mazda, that know jack **** about our cars.
good luck though!

peace

NoDOHC

I would guess the OMP

Keep your eyes pealed on ebay, there is usually a good one for sale there (not cheap though.)

tiamog

thanks i'll try to find an omp online and take care of that pefore i do anything else

none of you thind there mught be a short in my harness huh?

just thought about something. would it be possible to use the omp off my 88 se or no i know that a lot of things are different about the two cars. it's worth a shot to ask though

Snack

you drive an S5 rx7 which has electronical Oil Metering. The 88 se u speak of is an S4 which is run mechanically(has nothing to do with the ecu) so no u can't do that.

tiamog

ok thanks so my best bet would be to go ahead and get an omp for the car then.......... hey what if the light does not come on until i drive cause i can sit there and rev my car while it sits there andthe light will not come on but as soon as i drive it the light comes on and it will run rough would it still be the omp or could it accually be a short in the harness?

NoDOHC

Shorts in harnesses come and go, this seems to be a sudden and irreversible change, thus causing me to gues it is a failed OMP

Also, S5 OMPs do tend to fail at about the age of your car, so I am also speaking from experience.

Is there a reason that you suspect a short (damaged harness, PO hacked it up, the engine has een on fire, etc.)?

tiamog

there is no real reason to suspect damage to the engine. so i'll go with your suggestion and get an omp........ i'll let my ignorance show but is this a hard task replacing the omp

FC3MAN

Hmmmm, yeah diagnosis on the old cars isn't as easy as plugging in a scan tool to your honda civic, the code discriptions are vague at best,and,magus2222 the problem with your mazda techs these days is they weren't even in grade school when the second gens came out ie no factory training,ie no clue. I'd much rather a professional work on my car, than an accountant playing backyard hack or internet professional. I have that OMP you need,drop me a line, and find you a mazda dealer with a master tech on staff, and remember we don't work for free if you want more info you'll have to pay for the test to be done to pin point the problem or your just haning parts and wasting money

HAILERS

Go to the ONLINE AND FREE Factory Service Manual. Download the FUEL AND EMISSIONS section. In the front of that section is how to download the Fault codes. It's a simple procedure. You jumper a single, green plug near the Lead coil assy to ground then determine the codes. It is simple to do.

It sounds like you had at least three Fault codes. One being the OMP and a possible Trail Coil problem.

So if you download the same OMP fault code, then go download the LUBRICATION section of the same FSM. In there you will find procedures for checking the OMP wiring.

No digital meter? Farm it out or become a *parts swapper* (expensive).

And about the trail coil Fault (if indeed there was one there). If the signal from the ECU to the Trai Coil is lost, then the ECU will kill the operation to the Trail coil assy. BUT let it be known, if a Lead coil is still working, you'd NEVER notice the Trail coil not working. The Trail coil working or not is NOT noticable at all.

And the wiring from the ECU to the coil assy's is a straight shot and there is NO reason to think the wiring is the problem unless its at a termination at either end. Personally for right now I'd forget about any Trail coils assy problem. Concentrate on the possible OMP problem.

Search for LIMP MODE in the search function of this forum and you'll see this OMP problem has been encountered before.

NoDOHC

Actually, changing the OMP is not that bad.
You just have to make sure that the drive is alligned properly and that you get the oil lines in the right places (they should stay about right).



This section describes the troubleshooting of the OMP

02_Lubrication_system

This Section contains all the information you should need for the OMP (if you scroll through it).

01_Engine

This section tell you how to retreive the diagnostic codes from your car and how to interpret them.

04B_Fuel_and_emission_control_systems_non_turbo

Sorry about that other link, I forgot that the forum does not use HTML

NoDOHC

The tach will cease to work if the trailing coil is not firing, right?

HAILERS

Right as rain.

1990TurboII-75K

You might find this thread interesting.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-mop-ecu-failure-diagnosis-710938/

Your problem sounds similar to mine. Check you MOP with the Test Table in the thread above. If its OK then check back through the system - harness and ECU.

texFCturboII

iTrader: (17)

yup, get that OMP fixed NOW, before it fries your ECU.... I recommend replacing both at the same time, preferrably from the same car. If the MOP does toast the ECU, like on mine, you're in a world of pain and chasing CEL's!

Background:
1- replaced the waterthermosensor to learn the OMP was bad, in fact it wasn't even going into limp mode until I replaced the thermosensor
2- replaced the OMP and the ECU told me that now the knock sensor was out!
3- detonated cuz i didn't know my knock wasn't working
4- saving up for a rebuild cuz of a chipped seal

Get it fixed before it kills your car too! Its not hard, 3 bolts, two connectors, and if the feed lines are in good shape then leave them on, it makes installation SO much easier.

tiamog

ok i have the codes at my house from the test and if i'm not mistaken they were 1,27,and 36 they said that it refered to omp mop (step moter)ei. ecu failure or short in the wiring harness they also said something about the trailing coil going bad but they chkd it and said it was firing correctly. so thank you all for your help hailers and NoDOHC and texfcturboII if any of you have or know of a link with steps to swap an omp please send it to me thanks again

texFCturboII

iTrader: (17)

Its really simple! It's just three bolts, two you can reach from above, and one you are going to have to get under the car for. If your oil injection lines look clean and not clogged up you could re-use em, and that makes the job much easier!

disconnect the battery..... duh......

1) drain out all the oil
2) get out your trusty 10mm wrench / socket and remove the 4 bolts connecting the lines to the OMP. Hold on to the little aluminum plate, you'll need it unless your replacement has one too.
3) remove the two bolts you can reach attaching the OMP to the block, then get under with an extension and ratchet the other off (this one is a little tricky and requires some wierd arm placement, but once you get under there you can figure it out.)
4) remove the old OMP from the block, and disconnect it from the harness hold on to that hard gasket, make sure it's in there when you put the new one on.
5) get the new OMP, and follow those steps backwards to re-install!
be sure to pre-mix for a few hundred miles to make sure that the oil feeds through the lines to the injectors!
Good luck!

tiamog

ok sounds good but could you be a little more detailed about (pre-mixing) cause i'm not sure exactly what and how to do that........ i know i'm helpless to meyself but thats why i came to you all. thanx

phoenix7

premix- 2 cycle oil you add to your gas tank when your OMP is bad/dead.

On an S4 = no problem

on S5 = limp mode still.

Just fix the OMP and forget premixing. I've been reading about the OMP taking out the ECU also so you might need another one.

Check post #8 of the FAQs for FSM.

NoDOHC

From my point of view, It seems that the short in the harness is unlikely.

Here is my reasoning:

S5 (1989-1991) RX7s have Metering oil pump failures quite frequently when they get older. (You can do a search on the forum for "limp mode" or "check engine light" or "no power" or "my car won't rev", etc.)

Although wiring harnesses do fail, there is no indication that your harness is damaged except for it's age and the fact that you are throwing codes and in limp-home mode.

Wiring harness problems usually come and go (at least at first). There is very little chance that the code would be thrown everytime that you start to move if it were only a short or open circuit (there are some exceptions to this rule).

I could theorize about this for a week (or more). I originally thought that replacing the OMP would be the quickest and most simple check and if it didn't fix the problem, you have a spare.

Then I looked at OMP prices on eBay.... WOW... Before you spring for $200.00 on eBay, some additional diagnostic work is prudent.

With that kind of expense at stake, parts changing (while easy) is not advisable. The diagnositc skills that you will learn here will be beneficial for the rest of the time you own your car if not for the rest of your life.

Since all three codes thrown relate to the OMP, I would start with it.

I would recommend following the FSM procedure for determining if the OMP is ok. If it passes the FSM test, then I would suspect the wiring harness and/or ECU.

The wiring harness can be tested with an ohmmeter and a visual inspection, while the ECU and OMP basically require teh FSM procedure.

These are your possibilities listed in what I consider the order of probability from what I have read and what I have experienced:

1: OMP stepper motor or position sensor has failed.
2: OMP stepper motor or position sensor has failed and has damaged the output driver portion of the ECU, making the replacement of both necessary.
3: ECU OMP hardware driver had failed, causing the OMP to appear bad.
4: Open circuit in the wiring harness (read: broken wire or corroded contact).
5: Short circuit in the wiring harness (read: one wire rubbed through and touching another bare wire or the body/engine).

This era of Mazda electronics had a serious problem with cold solder joints. ECU failures, while almost unheard in newer cars, do occur on these.

Anyway, if anyone else can think of another possibility, or thinks that the probability order is incorrect, please feel free to comment/correct.

tiamog

all of this info will help me out so much thanx