xmcnastyx

I have this issue I haven't been able to pinpoint the cause of yet, I have an 89 gxl mt completely original, 83k miles that runs really well. fires right up. idles perfect. but loses all power past 20% throttle. you can bring the car to redline if you keep throttle below 20%, I do get a check engine light but it doesn't come on until you start giving the car more than 20% throttle. if I try to check the cel codes via the jumper wire method my cel will come on for one second, shut off, then come back on and stay on. im totally unable to read any codes. I have checked tps resistance and checks out well. afm checks out good as well. ive searched around the forums and haven't had much luck finding this exact issue, its not the normal 3800 hesitation because it will go all the way to redline but if you press more than 20% throttle the engine totally cuts out and starts bucking as if fuel is cut or something, I appreciate anyones input

insightful

limp mode, most likely a bad OMP...

xmcnastyx

I have a new omp on the way because I suspected that might be the problem, do you know why I wouldn't be able to get cel codes? its supposed to store the codes until the battery is disconnected but my cel will stay off until I get to 20% throttle, after that cel comes on and starts bucking/ no power.

insightful

who said the ECU stores codes? OBD1 vehicles don't generally store codes, you have to do the code checking procedure after a code is present. the vehicle does a self diagnostic test during and after startup, but that doesn't guarantee a failing part will throw a code until the engine is warm and run for a bit.

i don't know what you're doing wrong, you sure you are grounding the single wire green connector by the leading coil?

xmcnastyx

Yeah if I turn the key without the jumper wire the cel will stay on forever. If I put the jumper wire on the single green connecter to ground the cel will turn on then shut off for a second then stay on forever. If I start the car the cel won't show until I go past 20% throttle

insightful

are you trying to ground the wire after the CEL has illuminated with the key on and engine running? it will not hurt anything.
the code you're describing sounds like a pass with no codes present. the OMP code usually only occurs once the perameters are met, which is after the engine is running and often times slightly warm to fully warm to extremely hot(summer temps full operating temp).

xmcnastyx

I haven't tried while engine was running, if I start the car the cel wont illuminate until you start driving. your saying I should run the car until cel shows then add jumper wire while car is running to get codes?

insightful

yes, leave it running while the CEL has illuminated indicating a code is set and then jumper the single green connector to ground.

xmcnastyx

ill try that tonight when I get home from work. I already ordered the omp cause I figured that would be the issure, car has new plugs wires fuel pump and filter, tps checks out, injectors check out, I haven't had the time to dig down to the omp yet, I figured I would wait until I get my replacement

insightful

it almost certainly is the OMP, and when replacing it just be very careful moving the old lines, they are EXTREMELY fragile.

lduley

iTrader: (1)

Your ECU could be fried too. Theres been a couple threads with your exact symptoms with the CEL and the OMP fried the ECU

xmcnastyx

ill be sure to post tonight to see if I can get a code to read. I heard about the ecu problem too, I pulled mine and it looks okay. is there a way to check the ecu with a multimeter ?

insightful

that is possible but it isn't really all that common that i've seen. i run into failed OMPs quite a bit but honestly don't recall ever seeing a burned ECU first hand from it, though it does happen from time to time.

if it looks ok then it probably is, there is a pair of resistors that should be obviously burned if it failed.

i believe these were the ones:

Pete_89T2

iTrader: (4)

Actually the S5's do store CEL codes, as long as you don't clear them by disconnecting the battery. It will store codes that cause the CEL to stay on, as well as faults that don't necessarily trigger the CEL. I know this for a fact as I've been able to read codes off of mine, even when the CEL is not currently illuminated.

OP - here's a good how-to reference for checking the stored codes in a series 5 FC: 89-91 CPU Trouble Codes

Also, before swapping out OMPs or ECUs, be absolutely sure your wiring harness is still electrically & mechanically sound. A harness that tests well electrically (i.e., no shorts & proper point-to-point continuity) under static conditions is not necessarily 100% OK. These stock S5 harnesses are now between 26 and 29 years old, and most are rather crispy & corroded by now, meaning the odds of intermittent failure pretty high. I used to have all sorts of electrical gremlins with mine before I replaced it with a new one, including OMP related hiccups that put the ECU into the limp home mode. New harness and all those old intermittent problems magically went away.

insightful

perhaps that applies to some codes and not others, i believe as long as the OMP code is set then the car will be in limp mode so it is wiped each time you cycle the key.

xmcnastyx

Your help is greatly appreciated. I'll double check those resistors tonight as well. Im determined to get this car running. I'll post whatever I find tonight

Pete_89T2

iTrader: (4)

It is true of ALL codes, not just some codes or only the ones that trigger limp home mode. Case in point, I had removed my AWS (accelerated warm-up solenoid0 and disconnected that other solenoid valve that mounts to the backside of the UIM, which happens to be wired in parallel with the AWS, per the FSM wiring diagrams so the ECU won't throw a code for those unless BOTH devices are electrically fubar'ed. CEL would never come on for these things, nor would it induce limp mode, but as long as the ECU had power, the codes for these were stored & readable when I pulled them. Now obviously, if you had the CEL come on for an error that does induce limp mode, both the CEL and the limp mode would be cleared when you disconnect the battery - and will stay cleared unless the same problem recurs when the ECU is powered up again.

xmcnastyx

I can't pull any codes when I connect jumper wire and turn key to on. Do you think it's not storing engine codes because of some sort of wiring problem that doesn't give the ecu power with the key off which clears the codes?

xmcnastyx

Got the cel to flash a code while the car was running. I got one code #27 for the omp. I'm gonna go hunting in here for the connections to check them with the multimeter

insightful

shrugs, your experiences haven't been what i noticed. case in point above.

i tend to pull codes once with the car off and once after a test drive, i often times get codes that aren't there just after the self test..

xmcnastyx

So I replaced omp last night and still getting code 27 and no power. At this point it has to be a problem with the wiring harness. I did some checking on my ecu and at pin 1a I should have constant 12 v power but for some reason I only get 12 v when key is turned on. Which is probably why my ecu isn't storing codes. I'm thinking I need to splice a new section of 16g wire with a 10 amp fuse directly to the battery and see if that helps any

SlowDC5

I just bought a 91 RX7 last night, it has the same issue where the car "breaks up" after 20-30% throttle is applied, what are you jumping to check the car for codes?

xmcnastyx

RX7 FD & Series 5 Error Codes that will give you everything.

NCross

iTrader: (18)

Bad OMP would not allow you to go to redline. Correct me if I'm wrong... When it happened to me years ago I seem to remember it hit a wall at about 2000RPM give or take and would not go past that mark at all. CEL was constantly on as well.

xmcnastyx

Yeah I have an rtek 1.0 that should be here tonight. Gonna delete the omp and run premix maybe do a mechanical on leave from an s4 if I ever need to rebuild the motor