bw993

My M-Tune is at least 3 years old. I also use a liquid filled fuel pressure gauge on the fuel rail, which seems to reduce the needle bounce with the gauge.

Tom M'Guinn

If you log, check the MAF voltage when the car is trying to return to idle. After a big turbo blast, the voltage on some MAFs take a while to return to normal idle levels and as a result flood the motor. Compare the MAF voltage at idle when fully warmed up, to the voltage you see as the motor dies. If the voltage coming down too slowly, it can help to open your idle screw as much as possible without overly increasing the actual idle RPMs. Josh may have other tricks unique to m-tune too, not sure. Worth checking anyway -- though of course your issue may be entirely different.

markl951

Good point Tom. I'm in the middle of installing a more permanent wideband O2 sensor/gauge & then I'll do some experimenting. My datalogger captures the MAF voltage. I need to change the label on my plots though as it still says AFM .

blade7

Have you resolved your idle issue yet ?

mahoney944

Unfortunately life got in the way and my m tune resolution is on hold for the moment.

markl951

Not trying to highjack mhoney944's thread, just hoping to sort the running rich / engine shuts off diagnostic for myself and everyone else...

Hooked my datalogger up and went for a test drive hoping to log the post WOT engine shut down behaviour i've been experiencing. Of course I couldn't get it to happen. I haven't seen people log MAF voltage vs boost / RPM so I can't compare but I didn't see any odd behaviour with the MAF voltage as it transitioned to idle speed. I did notice that I was running rich under boost, dipping into the high 9's at times. I'd like to implement an adjustable FPR but for the time being, FQS changed from 0 to position 2 (-3% fuel on my pre-Lindsey M-Tune according to Joshua).

More road testing / logging... AFRs are a whole point higher at max boost so better now at 10.9 min AFR. At Idle and cursing speed, AFRs run around 14.5. Still going to look for an adjustable FPR solution though as my 3.2 bar Bosch regulator is probably still too high.

Again the engine didn't shut off after any WOT off ramp runs but I wasn't able to sit too long at idle either as there was too much traffic on the road. When I got back home I left it idling in the driveway for a while. All steady for nearly a minute then AFRs went from mid 14 to 16-17 for about 30 seconds then back to normal. Then all of a sudden the MAF voltage kicked up from .67 to 1.25 volts. Half second later the RPMs started increasing to about 2000 RPM & AFR began dropping to about 13.2. Never touched the gas pedal. AFR then went lean >22 & the MAF voltage and idle speed settled back down. About 10 seconds later the RPMs dropped & it almost stalled. AFRs went lean then rich and back to normal as it recovered. I wonder if I hadn't adjusted the FQS to -3% fuel if it would have shut off like I'd seen before?

The datalog screen capture below starts just before the AFRs increased from normal to slightly lean. The unexplained MAF voltage increase it at the vertical cursor line.

I can't explain why the MAF voltage would just increase on it's own like that. I'm sure there's a clue there. If the ISV were stuck open would it allow outside air to flow in past the MAF sensor?

I plan to go back through things and check for leaks one more time & maybe reset the idle while bypassing the ISV as Joshua previously said this was an important step in setting up M-Tune correctly. Might also check my stock O2 sensor. All these years of running "Guru Chip" rich have probably not been kind to that sensor either.

For reference, my car is mostly stock 86. Stock turbo, stock (but shimmed) wastegate, 3" exhaust, no cat. Manual boost controller. Bought & installed Joshua's full M-Tune kit including his 80 lb/hr injectors back in FEB 2014. More recently, added LR venturi delete kit & all new vacuum hoses.

Rogue_Ant

Yep, needs to be 3.0 bar. The extra 0.2 bar of fuel pressure is probably worth 0.5 points of AFR...


Could be a few things: bad grounds, sticking ISV, oil on the MAF sensor, bad AIT circuit, bad coolant temp circuit, etc.


That most likely tells us that the TPS is working (or at least that it was working at that point). If the system is in 'idle', and the RPMs get too high, the DME will completely cut fuel to force the engine RPMs to drop - this is why you saw the AFR going lean for a short bit. Once RPMs are back in 'normal' range, fueling is re-enabled, and a little extra is injected to help recover the engine from stalling.

So, basically, what you described is 100% correct DME/engine response for a "run-away idle-speed" situation.

If you look at intake pressure, you see a loss of vacuum corresponding with the rise in MAF voltage. This means the engine is ingesting more air. More air = more power, thus the resulting rise in RPMs. What is allowing more air to enter the motor? Likely candidate here is the ISV. The real question is why is the ISV opening more than it should? This could be a intermittent TPS sensor, or coolant temp circuit.

markl951

Good info Joshua. Thanks. Last year when I installed the LR Venturi Delete kit I also cleaned & inspected the ISV. Also replace every old rubber hose with new silicone hose. I know I have some cracked insulation on the wire harness side for the ISV, TPS, and MAF connectors but pretty sure I addressed those problems. None the less, I recently ordered replacement connector ends and will be rebuilding them completely. I'll re-check the ISV then a well. I know it's (mostly) working as I can feel it vibrate.

w/r to the MAF voltage, if the ISV is letting in too much air somehow, that air bypasses the throttle plate but it's still drawn in from outside air so in effect that air flow goes past the MAF sensor. Am I thinking of this correctly? Hard to tell from my data log what comes first, loss of vacuum or increase in MAF voltage.

I was expecting to see a higher TPS voltage at WOT but it maxes out at 3.6 volts. I had it scaled from 0-100% before in my data log so I never really looked at the absolute voltage. There must be some additional series resistance in the KLR's +5V supply line. Based solely on the resistance of the TPS itself, I was expecting to see ~ 4.5V at WOT. I measured +4.92V at the supply line so that seems normal. TPS resistance range meets spec as well according to the KLR test plan. Can you comment on measured TPS voltages? I notice your data logger doesn't offer that parameter.

Mike Lindsey

The ISV just loops air around the throttle blade, but it doesn't allow any outside air into the system. All air entering the intake is measured by the meter.

Typical TPS voltage we have seen with looking at many Mafterburner datalogs will be be .7 to 3.4v. It depends slightly on how you have your TPS and Idle stop screw adjusted. Yours is what we call a normal reading.

PorscheFanatic202

Where did you install a crankcase pressure sensor?

markl951

I threaded a barbed hose adapter into the top of a spare oil filler cap. It's not exactly a permanent solution but works good enough for diagnostic work. I run a short piece of vacuum hose over to a MPX4250A pressure sensor. The sensor output goes to my data logger. I'm using a 2nd MPX4250A sensor to monitor vacuum/boost pressure tee'd into the line that goes to the KLR.

markl951

I'm measuring 0.49 to 3.61 volts so good to know. Thanks Mike.

Wojo7

I'm still struggling with my idle, I just can't seem to get it to run steady with the O2 sensor plugged in, I thought it may be the sensor so I replaced it ( 2nd time ) but it is still hunting and very erratic. The good news is that it runs great with the O2 sensor unplugged, just a bit rich, 13.2 but very steady. I really don't know what is left to replace, I've been trouble shooting this for 6 months with Joshua who I have to say has gone way above and beyond to help me. He even donated a logger and promptly examined and commented on the many logs I sent him. In the end I believe I was suffering from a few different problems most of which I've sorted out including a new ECU. Just can't seem to iron out this idle bug. I have a K27/6 that I've been waiting to install but I'm afraid to touch it. The weather is starting to get nice here so I think I'm gonna close the hood and put some miles on the car , I'm sure eventually the root of this problem will show itself.

blade7

Is it essential for you to run the O2 sensor ?

Wojo7

I don't think I really need it, the car is old enough to be exempt from emissions testing and I've removed the catalytic converter so I don't have to worry about it becoming clogged from running a little rich. I can lean it out a bit with the FQS but I'm pretty much spot on up top and I think that's way more important.