The always frightening electrical problems

[supraheelfan]

To catch you up to speed-car was hitting fuel cut under boost or aggressive throttle. Had mechanic come take a look and he said it was a bad cps. Removed cps and took it to a shop low and behold they said cps was fine, but fuel pump was bad. Got a nice Walbro put in however it would still hit fuel cut while driving. Now car won't even engage the starter; I got power coming from ignition to clutch then to starter relay however only the bottom two pins are hot (on the relay). Should there be another wire with power going to relay? I can jumper relay and it will try to crank but will not fire up.

[cre]

Just to catch who up on what? Always better to keep your posts about a given problem in the same thread... if it's getting too polluted let a mod know and we can see about pruning out irrelevant or dead end posts and suggestions.

A fad fuel pump doesn't feel/act quite like fuel cut. Test the AFM and check for leaks in the intake system for that.

Have you even checked for diagnostic codes?

Where the original thread on this? I'm going to merge this one and that one.

[supraheelfan]

no previous thread just wanted whoever replies to know what I'm dealing with. Error codes 12, 21, and 24. I've looked for vacuum leaks (no leaks) but haven't checked AFM yet.

[cre]

So codes for: CPS or ECU, Oxygen sensor or ECU and AFM temp sensor or ECU.....

The code 12 may be set if the vehicle stalls and is restarted by 'popping the clutch' or if it is push started. So if you've done either recently you may want to clear the codes and see if this one returns. If it does a bad CPS, wiring, fault in the starter circuit or the ECU may be to blame.

The code 21 well, a bad oxygen sensor won't cause a significant change in the fueling. The ECU is SUPPOSED to disregard the OX input after a minute or so of an 'out of bounds' signal. You may disconnect the O2 sensor to put the car into open loop operation to see if it drives any better.... BUT even if it does drive better that doesn't mean the O2 sensor was to blame.

Code 24 is important. The ECU must know what temperature the incoming air is in order to properly adjust timing and fuel. Test the AFM before anything else.

[supraheelfan]

If I clear the error codes would I have to drive the car again for the codes to show back up?

[cre]

I already answered that. To clarify: Some will show up at the ECU power up diagnostic; Some will appear when you run the car for a couple minutes (just idling will do); Some require the engine to be up to normal operating temp and running; And some require you to drive the vehicle to give it a chance to sample data at various load levels.

[supraheelfan]

I have a question: A mechanic I just recently met said since I have a used JDM engine and the original ECU wiring harness from the old 7mgte, that I need to "upgrade" by getting some new sensors so the ECU can read the signals it needs to operate the engine. Is any of this true? He wouldn't clarify which sensors he was talking about and he said there is about 3 sensor that needed to be upgraded..

[cre]

The ONLY sensor which isn't cross compatible is the oil pressure sensor. If it's a California car (originally sold in Cali) the ECU will also be expecting signal from a sensor in the EGR cooler which other MKIIIs don't have; As you don't have an error code for that sensor I assume that to not be a Cali vehicle or the swap was more complete.

Does your oil pressure gauge work?

How does he know it's JDM? It's not written anywhere and aside from the oil pressure sender and the way the coolant is routed there are no other differences.

[cre]

I suppose it is worth mentioning that there were a number of changes made to the electrical system throughout the '89 model year. Pretty much all of the components are cross compatible but most have different plugs, the wire harness changed, the external HAC sensor was built into the ECU, the ECUs are different (many different models actually but the only significant difference it the redline depending on wether the engine has a 6M or 7M crank). The AFM and TPS connectors are the same as are all of the temp sensors and the oil pressure sender, the CPS is different and you wouldn't be able to plug it in and the wrong TPS will plug in but the interface tabe will be clocked 90? differently than the tabs on the throttlebody. The significant differences in ECU are highlighted by the harness connector colors.... Basically, if plugs and connectors are yellow it'll work and if they're both grey it'll work.

Again, it doesn't sound like any of this is the case with your vehicle.

[supraheelfan]

Actually my oil pressure gauge did not work for a long time until recently my dad and me installed a Prosport oil pressure gauge, but before that it didn't work at all. Still no error codes and the only lead is this new mechanic however I don't know if he is right or just trying to get more work ya know.

This is off topic, however my dad and I have been in an on-going debate about the oil pressure sender; Does the Prosport sender need an adapter to work? The reason I ask is because my dad hooked the sender up (somehow) and now the gauge reading is way off. Just wondering cause the sender was really hard to get into the block and from the search on the internet the sender needed an adapter to go from NPT to BPT or something like that. Any knowledge about this is appreciated.