Last night while out for a drive I noticed the engine was sputtering a little while
crusing at between 2700-2900 rpm. The AFR readout was 10.9 -11.5.
If I accelerated the sputtering went away and the AFR adjusted to 11.8-12.4.

This afternoon I went out for a drive and the car ran fine normal AFR while crusing, ~14.5 . I drove it all afternoon and she ran great.
While on the way home this evening she started sputtering again and the
AFR while crusing was 10.9- 11.5 again. If I accelerated the sputtering stopped and the AFR adjusted to 11.9-12.5 . At idle the AFR is 14.5-14.9
and she idles fine.

So it looks like while crusing she is running to rich for some reason.

Any ideas where to look??

 

maybe the 02 sensor is failing intermittently, reading leaner than reality and causing closed loop to richen the mixture.
hmm could be the TPS also.

 

Just to rule out the TPS, I'd unplug it with the car running and see what/if anything happens, check pins 4 & 6 at idle positon, as you should get 1 ohm. This seem to happen more when the car is warmed up?

 

Hi Tim,
Check the TPS and the engine temp sensor. Of course, make sure there are no leaks and all ground connections are clean and making good contacts.

Email me directly if I can assit.

 

Thanks for the suggestions.
The O2 sensor is new.
The TPS sensor is new 2k ago , but it wouldn't surprise me if the harness
is bad as I've had other harness problems.
I'll check the Engine temp sensor and the TPS and it's harness.

Ski it's not temp related.
John thanks.

 

Just an update.
Useing the Zeitronix I logged the TPS signal and it looks ok. Follows throttle
input well.
I pressure tested the intake again. Found a leak at the ISV again. I fixed this again. (probably should replace it)
The car no longer sputters.
The AFR is mostly 12.6 or so while cruising.
Ambient temp is about 35 degF this evening. Does this have anything to do with the AFR being on the rich side?
The FPR is a fixed 3bar Bosche unit. At idle I'm seeing about 45psi on the fuel rail.

 

Hi Tim, 12.6AFR while cruising is a bit rich. Which FQS are you using? How about the SMT6, what values do you have. This should be an easy fix.
BTW when do you hit 1 bar boost? Can you data log boost with the Zeitronix?

 

HI John.
I've got to check the smt6 and see what the O2 sensor is reading.
I don't recall what the FQS is set to. It would have been set to whatever
you recomended. I'll check it also.
I know I can dial out some fuel but my concern is really, what changed ?, The AFR's had been mid 14's while crusing no load.

Yes I can log the boost. Last I checked I was seeing 1bar at roughly 2950rpms.
I've got a small exhaust leak that still needs to be tracked down. I can smell
it if I'm boosting alot.
My guess is after the leak is fixed and the AFR problem is sorted I'll see 1bar
by 2800 or so.
Thanks for the help , I'll let you know what I find.

 

Check the FPR make sure no fuel is getting sucked in via the vacuum hose..
Was the car fairly warm when you noticed the richer mixture? Just making sure you are not in the cold fuel enrichment stage.

 

John , I'll check the FPR.
Car was warm about 20 mile trip.

 

Took car out today with laptop to log the SMT6 AFR's
Car is running great no problem.
Started thinking of what was different today. Then realised that the last
times I had driven the car it was dark out.
So I turn the headlights on and presto , problem surfaces. Turn lights off,
AFR's are perfect.
SO I tried it again and found that when the lights are up but not on still have the problem.

How can having the lights up effect the AFR's that much?

 

Where did you hook up power for the SMT6 and the MAF?

 

Power for the MAF is from the test port under the hood.
The SMT6 is powered off the DME .

Ski I was thinking along these lines also. This is why i tested with the lights
on and off while up. I'll have to look at the wiring diagram but I don't think there is any power draw to keep them up.
Having the parking lights on doesn't effect the AFR's.

 

Where have you placed the MAF sensor on your car?

 

It's about where everyone else has theirs.
Let me find a pic.