Croyston

Another day, another issue with my FD.

Car details: 1993, manual trans, mostly stock save for suspension and exhaust. Recently rebuilt motor, new plugs and leads, re-manufactured stock ECU.

The Issue: When I take the car up to about 5000 RPM in neutral or in gear, it starts running super lean and (presumably as a result of the AF ratio) begins to stutter and lose power. It almost acts like a rev limiter of sorts in that it will rev up to 5000, bounce down to about 4200 and then I can bring it back up to 5000 and repeat seemingly indefinitely. I haven't had the opportunity to test higher gears, but this happens in gears 1-3 at basically the same range for each +/- maybe 200 RPM. The only different thing that only seems to be happening in 2nd is that occasionally after taking it up to 5K, it will drop down to something around 2500 RPM and then won't go above ~3500 RPM for a few seconds afterward. If I throw it in neutral or a different gear following this, the anomaly goes away and I am back to issues at 5K.

My suspicion is that I have an issue with a solenoid although I'm not yet sure which one it may be. If anyone has any suggestions I'm all ears. I need to get this car done...

Thanks all

Barry Bordes

Could be a fuel filter or pump.
Do some tests per the manual.
Barry

Croyston

Quick update:
Replaced the fuel filter so that's out. Don't have a pressure tester so I can't presently eliminate the fuel pump entirely but, based off some new information which I will disclose below, I don't think the fuel pump would likely be the culprit.

So the new info: It seems this air/fuel issue is not actually tied to RPM but rather throttle position. I can get the same symptoms to occur in the same manner by quickly depressing the throttle down to a certain point (eyeball estimate about 2/3 open) or by steadily pressing to that same throttle point. On quick depressions, the engine only gets to about 3500 RPM before dropping power but the air fuel and power loss effects are the same as described in my initial posting. I haven't been able to dig through the manual yet to see, so has anyone run across any solenoids or switches that would activate/ de-activate in this throttle range? I was thinking it could be something in the double throttle control system. I will hopefully be able to fully test the fuel pump soon and I'll update my findings as soon as that's done but I'd appreciate any other suggestions the community may have in the meantime. Thanks all

Croyston

Another update/ partial solution:
After doing some tests of the fuel system I've figured out a couple things. First, the pressure test revealed that my system is operating at constant pressure at ~35 PSI which is slightly high for standard operation (which should be around 28-32) and slightly low for high load operation (36-38). I also discovered that a vacuum hose going into the big pressure tank on the top of the engine had failed so I wasn't obtaining proper vacuum. After fixing that issue, the weird ~3000 RPM issue is gone and the ~5000 RPM issue has changed slightly. Now what happens is that when I take it up to that range (either quickly or slowly, makes no difference now), I still get some funky stuff happening with the A/F ratio (more or less the same as before although possibly more erratic changes). The big difference is though I never get lean enough of a mixture to cause the power losses that were happening before, so I can now go up to redline and hold at Revs above 5000. The problem is that I get some stuttering and backfires above 5000 still and the operation is clearly not healthy. This tends to make me think it may be the Fuel Pump Relay (speed) (e.g. the one on the relay bank at the front of the car) not working, or possibly the pulsation damper for the injectors isn't working properly when the secondary injectors kick in. Thoughts? Anyone had this issue before?

FührerTüner

iTrader: (5)

Could it be that you tuned in shitty conditions, and now that theyre fixed, you need to retune?

Croyston

It's been awhile since I've logged on, and unfortunately I do not have much news on my FD issue...

First and foremost, I think the car does need a tune (although right now I'm worried that a tune would reveal a problem with my ECU, as I have chased down some issues back to that area). Does anyone know of a shop near the Castle Rock, CO area who can either A) test my ECU on vehicle and/or B) tune it to factory U.S (non-California) specs?

Second, I've discovered through some testing that I have some solenoids (specifically the charge control and double throttle control solenoids but there may still be others) that are not presently functioning. I have tested the solenoids directly and they aren't sticking or anything like that, and they are getting proper voltage to them and past them back to the ECU. If I read the voltages on these circuits with the respective connector disconnected from the ECU, they both show 12V with the ignition in the on position, but show ~4.5V with the connectors connected to the ECU. This smells like an ECU issue to me due to the fact that the manual says these solenoids should be at >1V at idle and 12V after warm-up/ above 5300 RPM. Has anyone seen this before?

smokimon001

Are ur secondary injectors getting signal from ecu at 5000 rpm?