AlexE

Well I am a little stumped right now and would appreciate some feedback.

I am officialy chasing my tail at this point. The car runs fine/smooth/strong/18-20mmhg when it has warmed up ONLY when the TPS is unplugged and I set the idle to +- 1300 rpm. I wil give you some background information (troubleshooting results) but the main question I have which would help me find the problem.........

WHAT does the dme ignore when the TPS is disconnected and only runs on partial throttle maps?????

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Car Setup:
Tial 38 with 0.8 bar spring
AVC-R disabled so I am running 0.8 bar (11 psi) only.
Fuel pressure has been played with from 45-52 psi.
Maf/chips and dip etc


A. Scenario - Car cold to first line on temp guage: (car runs fine)

Boost builds strong.
Boost stays pegged at 0.8 bar
idle vacuum 14-15 mmhg
Wideband reading 14.7 + - .1
idle solid 840 +-
Fuel pressure remains pegged where it has been set.


B.Scenario - Car warm to hot (second line) (carstarts to hesitates/bogs), the idle begins to wander erraticly

Idle starts to flutter (800-900) ... up and down......
idle vacuum 14-15 mmhg
Wideband reading AFR 15-16 as the idle flutters up and down. It even will lean out further while at idle....17 sometimes! The more the car leans out the more wandering the idle becomes.
Car becomes undriveable.
Fuel pressure remains pegged where it has been set.


Thanks.

testarossa_td

This is a new TPS?

AlexE

Yes one of three TPS. The latest being a new one that was tried.

When the TPS is disconnected it allows the partial throttle maps to be read. Turning the idle down then allows the car to run smooth and strong (albeit with the idle set around 1300 to keep the car from stalling out when full throttle is let off)

I checked the TPS at the engine harness and it reads correctly. The problem only occurs when the engine has warmed up.

WIth the TPS plugged in and engine hot it runs lousy at idle and partial throttle until it starts to rev up the rpm range...

It would make sense to me that even with the TPS plugged in ....... that at least at partial throttle it would smooth out as it does without the TPS plugged in.

Hence my question as to what is different in the two situations.......

Charlotte944

OK, this sounds like a temperature related issues, so my first suspect is the DME Temp Sensor II (the one with the blue connector). The DME uses this sensor to "tweak" the A/F ratio as a function of engine coolant temperature. When the engine is "cold" the DME will richen the mixture (Cold Idle Enrichment). As the engine warms the DME leans the mixture.

My second recommendation is to pull the MAF and go back to a stock AFM and air box/snorkle. If the AFM works, then check the MAF to see if it is measuring incoming air temp. The stock AFM has a temp sensor which the DME uses to compute air density. Once the air density is computed the DME "tweaks" the injector duty cycle to maintain a proper A/F ratio.

AlexE

Thanks Cliff for the reply.

I had thought the same thing when troubleshooting...........but I had not though of swapping in the old AFM. I will dig that up!

Now a couple of things two fill you in on the two suspecting sensors.

ONce the car heats up and the wideband starts to read a lean at idle and the idle begins to jump I tried the following.....

- The air sensor on the maf went from 2.3K ohm to 1.6 K ohms as the engine bay temps went up.. So I figured I would jumper the plug with a 2.2K resistor. The idle steadied out and so did the AFR. GREAT. Except going on the throttle it was jumpy and hesitating and car lacked power. No where near as good with the TPS umplug (power, smoothness,etc)

- The dme temp sensor starts reading at ~ 3 K ohms (can't quite remember exactly) (tried 2 different sensors) and it would drop to 200 ohms (conincided with block temp) as the cars temperature went up. NOW I shut the car off and plugged the dme sensor plug into another sensor I had sitting on the manifold. Trying to fool it that it was colder to richen up the mixture. Go and figure the idle improved somewhat and throttle response was better than with the airsensor plug with the 2.2 k resistor but no where near as good with the TPS plug unplugged.

........and thats why I am chasing my tail at this point.

fast951

Alex, did you try running with IAT sensor unplugged (resistor in its place) and temp sensor unplugged?

AlexE

Uhmmm didn't try it that way. But any time I would pull the dme temp plug it would stall out (makes sense with it dumping fuel)

The surface temp on the block read ~175 F

Now the sensors specify a 280-360 ohm spec........ but both temp sensors go down to 200 ohms....... They both could be leaning out too far. I may stick a 300 ohm resistor into the blue plug once the engine warms up and I start getting the symptoms (leaning idle, wandering).

A couple of things to try today. Jumping off a bridge was looking good yesterday.

Thanks for your help.

* another item for the puzzle. If the o2 sensor is unplugged when the symptoms occur. It really wanders like crazy and leans out further. With the o2 in place it tries to keep it at 14.7 but it can't compensate enough and leans out further 16,17 etc..

J Chen

Alex,
Check your soldering of your PB system. I have exactly the
same problem as you. I was chasing the problem for a couple
of weeks. First I thought it was the temperature sensor that
Cliff mentioned. I change it & problem still exist. Anyway it
suddenly dawn on me that I could have had bad soldering.
So I decide to resolder the wires & guess what, problem
gone. The one thing that I cannot explain was that during
winter, the car ran perfectly. It was only when summer came
that the problem appeared.

AlexE

Uhmmmm I did resolder the dme temp sensor plug a couple of years back. Uhmmmm maybe its coming loose?

Which wires were loose in your setup J Chen. I remember reading one of you posts with a similar issue when I was searching.....

Thanks. Sometimes its the little things like this. Another thing to add to my list to check.

fast951

Alex, of course double check all connections and triple check engine ground. I emailed you a test procedure to follow, hopefully we'll get to the bottom of this...

AlexE

Well went for a long drive after I ran some tests that John from Vitesse had given me.........................

*** I think I have been inhaling too many fumes! but read on ***
*** FOLLOW UP for anyone searching for the resolution ***

A LITTLE FURTHER BACKGROUND:
I completed this car 4 weeks ago and wanted to get it to an event on that weekend (John from Vitesse BENT OVER BACKWARDS IN SERVICE) to get me to my event. So I made it to my event....... I set the AVC-R to 11 psi and had a wandering idle issue at that time so I bypassed the ISV by jumpering test port B and C this had solved the problem...................

THe following week I replaced the ISV and had hoped that had solved the problem. I even tried to remove it by capping the two ends but the wandering problem remained if I removed the wire from the B and C. SO I began troubleshooting a couple of weeks ago..... and chasing my tail has led me BACK to where I started.

TODAY:

So after getting an email from John I went to run his test (did I mention he is extremely helpfull)........... I then decided to stick the wire back in to the test port B and C.

POOOOF car idles perfect every problem gone. I MEAN EVERY PROBLEM. I went for a 40 minute drive with the laptop hooked up. Car ran great. I had to add quite a bit of fuel with the smt6 to richen it up on the top end. THis turbo must be running MUCH more air than my last one.

ANYways problem is solved car runs FINE. Lets say PERFECT but only with the wire in place. ?

The odd thing is that I figured I would try and cap off the ISV on the intake and intercooler pipe side.........so I did that........but If I remove the wire from B and C the hunting idle still returns?

Now I am just cuirous about the answer to that last lingering question. DOes B and C have any other function asides causing the ISV to stay half open if you short it? Where else do B and C go ? Why does the idle hunt if the ISV is removed and shorting wire is removed?


*************


Thanks everyone for the the help.

BIG THANK YOU TO JOHN. I can't tell you the level of service this man gives. Truly a huge asset!

fast951

Alex, glad you got the problem figured out, it's always a pleasure assisting customers such as yourself.
As soon as I get a minute, I'll look into B&C in more depth and will email you.

wior

I am having a similiar problem, what is the B and C ? Can you forward me the
test that John sent to you.
thanks
Victor

J Chen

Wait a minute, if the idle stabilizer stays half open,
would not boost pressure leak through it ?

AlexE

Heheheheh J Chen.......... Well I never said it was a good solution.

EDIT: I am a goof. Yes you are right........So at least I should plug the holes for now!!

We have other dilemnas. THe car runs perfect like this. YES its weird.

The question that needs to be solved is WHAT else does the shorting out of B and C do????

The miniute I remove the wire it goes haywire....... roaming idle ...leaning out....... ( with or without the ISV in place so your point is a good one so at least for now I will cap off the intake and intercooler pipe side)