3.5 V8 with a 3.9 injection conversion runing to rich

Awkward · Mar 9, 2019

-TPS reads 0.35v & rises to 4.8
-MAF reads between Blue/Red & Red/Black 1.5v constant
-MAF reads between Blue/Green & vehicle’s Earth
With ignition on but engine not running 0.39v
At tickover 1.3v & rises to 3v at approx 2000rpm
-The prime fuel pressure is 30psi & rises to 39psi when reved
-Timing was set to 6 degrees then drove it till it pinked under load than wound it back a couple of degrees until it stopped pinking

Awkward · Mar 9, 2019

I thought it was the throttle potentiometer as well but it’s giving the correct values.

classic kev · Mar 9, 2019

TPS voltage looks slightly high to me. CO trim at 1.5v is high for non-cat car.
Have you checked the throttle pot for resistance and scaling?

Awkward · Mar 9, 2019

Throttle pot is clean & moves freely...
What would you set the TPI & CO trim at...?

classic kev · Mar 9, 2019

Throttle pot 0.27v to max 0.30v.
CO trim 1.0v

Awkward · Mar 9, 2019

Thanks, soon as I get the injectors back il give it another go....

Awkward · Mar 10, 2019

Kev,
Just been checking the EFI wiring loom checking for damaged wires etc and unraveled insulation tape covering the map resister to discover the resistor seems to be missing completely....!!!

classic kev · Mar 12, 2019

I've never tried unplugging the tune select resistor so not sure what would happen.
I could only suggest you get hold of the correct resistor and plug it in and see what happens??

classic kev · Mar 12, 2019

O.K. just had a quick breeze through some info I have and it turns out some NAS spec motors didn't have a tune select resistor. In this case, apparently the ECU will assume a "white" tune which is a cat tune and O2 sensors are required.

If the ecu assumes a cat tune but no O2 sensors are fitted it will run really rich and drop in to limp mode.
I think I would buy the correct tune resistor - if non-cat then you need a GREEN one. You will need to unplug the ecu, connect the tune resistor then reconnect the ecu. Then you have the fun of setting it all up from scratch - Base idle, CO Trim and ignition timing. Yes, I know ignition timing is not related to the efi but your timing needs to be set to optimise how the engine runs.

I assume you also have a stock cam. I swapped my cam a couple of years ago and found that increasing the CO trim and advancing the ignition timing paid dividends so my 3.9 now runs CO trim 1.5v and 8 degrees advance at idle.

discool · Mar 12, 2019

All u need is a 470 Ohm at 0.5watt placed between terminal 5 of the ECU a single grey/black wire goes to the resistor, the other side of the resistor goes to ground, if u had one fitted.
My tune resistor is encapsulated in a white sleeve and partly wrapped with the EFI loom very near to where the ECU is positioned behind the drivers kick panel, something I only found out last year when installing a cable to a dash cam.

Awkward · Mar 12, 2019

Kev and friends thanks for all the help and I’m pleased to say the problem has been fixed...
In short everything needed setting up in the correct order and the final part of the puzzle was the green resister that for some bizarre reason had been cut off at some point. Shame I didn’t unravel the looms and find it was missing earlier...!!!!
Waiting for Kev’s box of tricks for the final tune up then we are all good on the engine, gear box & transfer box next.... !!!!

classic kev · Mar 13, 2019

Glad it's sorted. Always remember if the engine will actually run it will probably be something simple that causes rough running, the problem is identifying which bit isn't doing its' job properly. Have to say, never heard of a missing tune select resistor but hey we all live and learn.

lars-sport · May 14, 2019

Great thread, it might help me with my current fuel economy issues (8-9 mpg with a light foot). Two questions regarding the check engine light in the dash: a) would it come on with any with the above issues (maf, tps, resistor missing). B) is the check engine light supposed to come on when u switch to ignition and stay for a while? Mine (1998 3.9i D1) only flashes very short just to never be seen again.

lars-sport · May 14, 2019

classic kev said:
TPS voltage looks slightly high to me. CO trim at 1.5v is high for non-cat car.
Have you checked the throttle pot for resistance and scaling?

I just measured the voltage on the MAF for CO Trim and it was around 3V. The car does neither have cat nor lambda sensors. Could this be the reason, why it only makes 8-9 mpg? How can i reduce the CO trim, do I need to open the MAF?

3.5 V8 with a 3.9 injection conversion runing to rich

Awkward

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