Lean running ideas help
 

My car has recently started running excessively lean to the point that it barely runs at part throttle, as if I'm hitting fuel cutoff. However, if I floor it and trigger the WOT switch it comes alive and AFRs read in the 12's momentarily as expected but then goes excessively lean again as I back off the throttle. Unfortunately it's not practical to drive around my subdivision at full throttle. I have an AEM gauge that reads --- at higher than 19ish AFR as that is the limit of the gauge.

I have a wideband O2 sensor and gauge in car and car has ran fine and idled well on a 3 year 6k mile full rebuild. By fine i mean cruises at low 15 AFRs and idled right at 14.7, and gets into the 12s at full throttle. I'm running the stock chip (24 pin early 1987), stock intake with slightly bored TB and stock exhaust. 3.4 Mahle P&Cs around 10.2 compression ratio and Web21 cams. And I do feed the O2 signal to the DME

Prior to this I had some crank but no start episodes that resolved by simply disconnecting and reconnecting the CHT, Speed and Ref sensor connectors. So I'm kind of leaning toward thinking the CHT is the culprit, but some posts on here suggest a bad CHT will cause rich running, not lean.

I hooked up a fuel pressure gauge this weekend and found pressures of 33-34 psi at idle which moved down to 29 psi when throttle activated, and pressure held above 30 psi for 20 minutes after shut off. That's all I tested for now.

I also opened up my AFM and the track is not worn through, but the spring clip that looks like a "W" was slightly out of place, one end was not up on top of the toothed wheel and was sitting just off the wheel. I'll try to include a pic.

All the sensors CHT, Idle Control, throttle position, check out with ohmmeter and I think the AFM is behaving based on a limited ohmmeter test. I tested 2 injectors resistance and they were both in spec.

Injectors were cleaned and rebuilt 3 years ago. The CHT and ref sensors are 12 years old, and the FPR and fuel damper are both original.

The car starts fine and the AFR reads 14.6 after the gauge finishes booting up, but within a few seconds the AFRs start to increase and eventually go off the chart. I'm at high altitude but haven't checked that sensor and I've never touched the fuel quality setting so I assume it's stock.

What do you guys think?



http://forums.pelicanparts.com/uploa...1720407484.jpg

Check O2 sensor wire, not sure where you tapped into WB sensor to send it to brain but the green wire is a coax and outer shield is ground. If its touching signal wire weird things happen.

Signal to brain is not tapped into WB sensor if it is an AEM WB.

AEM gauge has a 0-1V output that is specifically provided for closed-loop mode and is to be connected to pin 24 of ECM. If car has been running fine until now, it was probably set up this way.

This is correct, its and AEM gauge that has an output signal for the DME in addition to the signal to the gauge itself.

I also tightened down the intake manifold and there were 3 or 4 bolts that turned a bit. If the engine partially sucked in an intake gasket how far off do you think the air fuel ratio would be?

This causes the ECM to ignore the O2 sensor.

Disconnect, or cut, the pin 24 wire at the ECM connector for testing, i.e. eliminate the O2 input as a problem source.