Question on ECU's

[mirage83]

What kind of difference is there (or isn't there) between an 89661-14141 and a 89661-14210 (aside from the car manufacture dates) ? Reason I ask is that my '88 is supposed to have the -14210, but the ECU has been replaced at some point in it's history and it now has the earlier -14141 (one year difference). The car does run, but I am having various electrical/electronic issues with the car and am wondering if having the incorrect date ECU in it might be causing some of the problems.

Thanks in advance.

 

[hvyman]

Are they both yellow plug?

Are they both manual or auto or what?

Yellow plug ecus are the same. Only difference is for auto and manual. There are outputs in auto engine ecu that go to the auto trans ecu.

Can use a auto ecu with a manual but you shouldnt use a manual ecu in a auto. Theres no gain in the difference between the 2.

 

[mirage83]

Both are yellow plug, both auto's. The -14141 in the car is for 87-08 through 88-08, and my date of manufacture is 87-11. I didn't think there would be a significant difference between the two, just unsure if there was enough of a difference to warrant finding the proper one for the date of the car.

 

[hvyman]

Nope wont matter. Engine doesnt know the difference. Car doesnt know the difference. Your problem is else where.

 

[mirage83]

Nope wont matter. Engine doesnt know the difference. Car doesnt know the difference. Your problem is else where.

Well, I suppose that's a mixed blessing. Thanks for the info Hvy.

 

[hvyman]

Yup no problem.

What problem are you having?

Have you checked your codes?

 

[mirage83]

Codes are clear, checked both manually under the hood and on my supermonitor.

One problem is with the #1 speed sensor. Can't seem to fix it even after trying out replacement speedo's, it still faults out and sets the OD light blinking. Second problem is engine related, when I run up the RPM's to about ~3k they abruptly drop to around 1k then pick back up and do it all over again. It's fine below that 3k threshhold, it's fine above that threshold, but if I'm running (or sitting in the driveway running it up some) around that 3k mark it consistently goes through the drop and recovery cycle until I pull the gas or give it more. I've checked for vacuum leaks, lose sensor connectors, etc., still can't figure this one out.

 

[jetjock]

Fwiw you can't have a bad speedo sensor and not have an engine code. That you replaced the speedo without joy also indicates this. Sounds more like a wiring problem.

The rpm cycling sounds like rpm cut. Check for code 51 in diag mode with the gas pedal pressed. If you don't get it that's your problem.

 

[mirage83]

Fwiw you can't have a bad speedo sensor and not have an engine code. That you replaced the speedo without joy also indicates this. Sounds more like a wiring problem.

The rpm cycling sounds like rpm cut. Check for code 51 in diag mode with the gas pedal pressed. If you don't get it that's your problem.

Sounds like a project for tomorrow afternoon. I'll recheck for codes (last time was several months ago) and see what shows up, but wiring is definately a possibility given how badly the car was "rigged" by the PO.

Thanks for the suggestions on the possible problems, it's really appreciated.

---------- Post added at 11:01 PM ---------- Previous post was at 10:49 PM ----------

Okay, so I couldn't stand the not knowing so I went on out to run the codes. As Jet Jock said Code 42 showed up for the speed sensor. Are any particular area's of the dash harness more likely to be an issue when wiring is suspect?

 

[jetjock]

Usually people check codes a bit more recently before asking for help :icon_razz

Has to be upstream of the connection where the signal splits. Or it could still be the speedo. Assuming you still have cruise control you can use its diagnostics to check the speed sensor further. Otherwise you'll just have to get in there and track it down. Check the cluster ribbon first.

As far as RPM cut that usually happens lower than 3K but it's worth a shot, especially if it does it when you stand on the pedal. That said a 3K cut off is normally associated with a disconnected AFM. You would have a code in that case though.

 

[mirage83]

Yeah, well, I've only driven it very rarely the last several months now, too many other things going on to really devote to troubleshooting her. Last night was the first time I've done any work on her at all lately, and wanted to ask about the ECU and stuff while it was fresh on my mind. You're right though, sorry for not having more recent info before asking.

Hopefully I'll have some time this afternoon to dig into it a little more and see what I can come up with, verify the pinouts and check continuity between the cluster plug and ECU. That ought to tell me real quick if that's where one of the problems is hiding.

 

[bioskyline]

Second problem is engine related, when I run up the RPM's to about ~3k they abruptly drop to around 1k then pick back up and do it all over again. It's fine below that 3k threshhold, it's fine above that threshold, but if I'm running (or sitting in the driveway running it up some) around that 3k mark it consistently goes through the drop and recovery cycle until I pull the gas or give it more. I've checked for vacuum leaks, lose sensor connectors, etc., still can't figure this one out.

almost sounds like a bad tps, might want to check that out as per tsm, might have a bad spot that wont throw a code, as 3k is around highway crusing speed.

as for the OD light blinking that not ECU related, that the ECT holding a code. sounds like the sensor in the trans might need replacing, does the abs still work?

 

[mirage83]

almost sounds like a bad tps, might want to check that out as per tsm, might have a bad spot that wont throw a code, as 3k is around highway crusing speed.

as for the OD light blinking that not ECU related, that the ECT holding a code. sounds like the sensor in the trans might need replacing, does the abs still work?

Hmmm, curious that you say that. Reminded me that back in March I was poking around checking connections and stuff trying to figure this one out I unplugged the TPS and the RPM drop went away. Didn't have a 41 code before doing that, was just checking everything I could think of that might have something to do with it. That sound like that the dead spot in the TPS to you?

I honestly have no idea on the ABS. Never had any problems with the brakes, and haven't yet had to really stand on them so I couldn't tell you if the system is woriing properly or not. I did have to replace the ECT as the one in the car when I got it was beat all to hell and I just didn't trust it, but there was no code for it beyond the one for the #1 speed sensor.

 

[bioskyline]

does sound like it. without a code the ecu wont go into limp home mode, and without a good sensor signal, the ecu cant pull the right fuel/ignition map for the current operating conditions, and run on the last map it pulled, till it gets past and corrects itself. or something along thse lines. also the fact that once you past that point its fine. the tsrm test should show if it does, as the 0-5v signal will stall at a point as you open the throttle plate

EDIT* use an anolog volt meter with a needle, it will give you a better idea than a digital one

ok, well the abs light should flash or be on stating a problem with it, wondering if the ect has an old code from the previous car, might try a clear and see if it pops up again

 

[mirage83]

I'll grab my manual when I get home and see about running some tests on the TPS, see what's what with it.

 

[3p141592654]

There are firmware changes between those two ECU versions, but the changes won't impact the problem you are having.

The fuel cut that comes from the TPS out of adjustment is not 3000rpm. Even with a stone cold engine (-20C) the fuel cut will be 2700rpm, and that drops to 1600 rpm with a warm engine. There are some conditions that cause a 3000rpm fuel cut. JJ noted and AFM failure will cause it. You will also get it for the following cases:

reduces rev limit to 3000 rpm if following is true
no SPEED fault & SPEED<=5 km/h, & throttle open, & in PN, & THW > 70C
plus either of the following:
1) THW > 120C and Count_HighRPM >= 6978h
2) Hit 6500 rev limiter & FuelCut3krpm >= F0h & FuelCut3krpm_Control > 5Ah

 

[mirage83]

There are firmware changes between those two ECU versions, but the changes won't impact the problem you are having.

The fuel cut that comes from the TPS out of adjustment is not 3000rpm. Even with a stone cold engine (-20C) the fuel cut will be 2700rpm, and that drops to 1600 rpm with a warm engine. There are some conditions that cause a 3000rpm fuel cut. JJ noted and AFM failure will cause it. You will also get it for the following cases:

reduces rev limit to 3000 rpm if following is true
no SPEED fault & SPEED<=5 km/h, & throttle open, & in PN, & THW > 70C
plus either of the following:
1) THW > 120C and Count_HighRPM >= 6978h
2) Hit 6500 rev limiter & FuelCut3krpm >= F0h & FuelCut3krpm_Control > 5Ah

Damn, good info in this thread. Thanks for chiming in with that. I'm going through the motions with all this and will hopefully have an answer or answers pretty soon on this headache. Appreciate all the help.