Odd Lean out problem, running out of ideas

[e30esque]

Hi guys. I have a 2.7 stroker (i head with seta pistons combo), running motronic 1.3 with the stock i chip. When I first put the thing together two years ago, It would run around 13.4-13.6 all the way to redline. After that I had an adjustable FPR on it for about a year. It worked fine up until this spring/summer. Then it would start out at 13.4-6 for a while till about 5500 rpm, at which point it would lean out to around 14.0-2. At this point, it has gotten worse. Now it starts out at 13.4-6 under WOT until around 5500 rpm at which point it drops like a stone to around 16.0 afr. Now I am back to a simple 2.5 bar fpr. I have newer 24.5 lb injectors btw ( I know, they are a little large). Things that I have changed in an effort to solve this problem: inline fuel pump and fuel filter, elimination of adjustable fpr, check for vacuum leaks, elimination of line that goes from valve cover to intake (now using a moroso catch can that I got for christmas, thanks dad!). Wondering if anyone can point me in the right direction.

[jlevie]

Check to see if the WOT switch in the TPS has failed.

[stumble_t]

how about o2 switch time? Seeing that the problem is more evident at higher RPM. A good sensor should be about 10 times a second.

[SpecM]

how about o2 switch time? Seeing that the problem is more evident at higher RPM. A good sensor should be about 10 times a second.

o2 sensor readings are ignored by the DME in WOT mapping

[e30esque]

o2 sensor readings are ignored by the DME in WOT mapping

Yeah, I kinda figured this. Also, I dont think that its the WOT switch seeing as how the AFRs are perfect in the whole rev range up until around 5500rpm.

[SpecM]

Yeah, I kinda figured this. Also, I dont think that its the WOT switch seeing as how the AFRs are perfect in the whole rev range up until around 5500rpm.

eh, it still could be the TPS. It just may be that the WOT mapping makes a bigger change in that area, or is supposed to.

[e30esque]

hmmm. Interesting. How would I test the switch?

[SpecM]

with an ohmmeter

its really just an on/off switch

[kennedy]

coolant temp aswell had that happen to me

[e30esque]

coolant temp aswell had that happen to me

What does that affect?

Checked the injectors today, clean as a whistle. Now has a 3 bar and the same problem. Also checked tps functionality (good), cleaned icv, checked for vaccuum leaks again, checked continuity of injectors, checked fuel pressure. Really at a loss here.

[jlevie]

I've been told that above 4500rpm at WOT the DME is ignoring AFM and O2 sensor data and is computing injector on time based on rpm, intake and engine temp. So seeing the A/F ratio go lean above 5000rpm would imply a problem with fuel delivery, rpm data, or temp data. With parts that have been replaced, the fuel system shouldn't be a player. But I'd still want to see what the rail pressure is as the engine runs up to redline.

It is easy enough to temporarily connect a 0-60 psi gage to the rail and clip or tie it to a windshield wiper. You can get the gage (commonly used in water systems) and the fittings needed from a Lowes, Home Depo, etc., and fuel injection hose from any auto parts house.

If the fuel pressure is proved not to be the problem, check the DME & intake temp sensors.

[e30esque]

Checked fuel pressure, right at 50psi up to redline. So you think the engine temp sensor is the culprit? For one, I know I have a white sensor vs the blue one it is supposed to have. I guess I reused my eta sensor. Also, I didnt know our cars had an IAT. Where is that located?

Thanks for all the help!

[jlevie]

The IAT sensor is in the AFM and is the small rod like thing sticking in the forward end of the AFM.

I would definitely replace the temp sensor with a new M20B25 part. Then see what happens.

Oh yeah, replace the 24.5lb/hr injectors with stock injectors. The DME may be adapting to the excessive flow rate by running down to minimum fuel trim, which will affect the WOT map. Unless you have drastically increased mass flow through the head the stock injectors have enough head room for this engine at WOT. After you install the stock injectors, reset the DME by removing power for 30 seconds.

[e30esque]

Would anyone happen to have a part # for the coolant temp sensor? I went to advanced auto today and they had one, but it was brown, not blue.

[jlevie]

I think the part you want is 12621710512