MV dropping

[jshot]

ok im back at. it. new pump in. tyring to troubleshoot MV dropping to knock levels. i verified pressure is rising 1 to 1. here are some screen shots of the scanmaster readings. this is at 18psi. only thing new on this car is ta49 and 3" down pipe (plus the new fuel pump. 340 ) i also ran this at 16 psi the mv still dropped but at a slower rate. prior to mods i would run 18-19#'s with zero knock.

scanmaster is showing 2 deg KR but on my gauge was in the red...

the pull starts at 838 mv at the start of 3'rd gear. by the top of third MV has dropped to 717 . The know always start at about 730. MAF is at 255 and battery voltage is good. fuel pressue rising 1:1 (58 psi & 18lbs boost line on of course) Log shows TPS4.39 but is actually 4.6.

 

[MikeS]

I see you have the pump hotwired, what about the ground wire? Your stock wire harness is approaching 40yrs old. I ran a new ground wire from the pump back to the battery when I did mine. Have you tried reading voltage at the pump harness?

 

[dynoman]

Have you pulled the injectors and had them cleaned ? Can you monitor injector duty cycle , if so what is it at WOT when MV starts dropping off ?

 

[jshot]

I have not upgrade the ground on the pump. i should try and read the voltage at the pump.
as for the injectors, they are not that old and have always been run with a clean filter and tank is newer. this is at WOT.

I did replace the filter this year and no change. also looks like the hanger is newer as well. not sure how old.

can the hotwire go bad? with the pump still run just without the direct voltage?

 

[dynoman]

What is the duty cycle ?? It appears that your pump is keeping up with pressure needs which accounts for the 1 : 1 rise in boost / pressure but what is the motor seeing AFTER the rail / gauge ? With a bad or dirty injector you will still get 1 : 1 but the motor won't see it . Just because the injectors are " not that old " doesn't mean they are ok . Check everything . good luck

 

[jshot]

What is the duty cycle ?? It appears that your pump is keeping up with pressure needs which accounts for the 1 : 1 rise in boost / pressure but what is the motor seeing AFTER the rail / gauge ? With a bad or dirty injector you will still get 1 : 1 but the motor won't see it . Just because the injectors are " not that old " doesn't mean they are ok . Check everything . good luck

is there a way to know the duty cycle?

 

[dynoman]

You can see duty cycle on a powerlogger or most aftermarket ECU's , not sure on a Scanmaster G . I would pull the injectors and have them flowed and cleaned . That would eliminate them from being the source of the problem you are having or fix it .

 

[salvageV6]

I'd throw some octane at it, can of xylene on a quarter tank of 94, or 4 gallons of 100 octane at fill up time and see if it goes away.
Then again the downpipe could be hitting the A/C heat shield or control arm etc.
Easy enough tests compared to others.
Did Eric reburn the chip or need to for the changes?

 

[dynoman]

I'd throw some octane at it, can of xylene on a quarter tank of 94, or 4 gallons of 100 octane at fill up time and see if it goes away.
Then again the downpipe could be hitting the A/C heat shield or control arm etc.
Easy enough tests compared to others.
Did Eric reburn the chip or need to for the changes?

The problem is his O2 mv reading is dropping to the low 700's like it's going lean .

 

[dynoman]

Did Eric reburn the chip or need to for the changes?

Good catch , different turbo moving more air .

 

[chris romani]

Good catch , different turbo moving more air .

He’s only running 18psi plus he said he added more fuel through the chip.

 

[jshot]

Good catch , different turbo moving more air .

I thought about that. That’s why I dialled it back to 16psi. I can try adding fuel back I now that I put the new pump in. But I don’t have high hopes

 

[jshot]

Did Eric reburn the chip or need to for the changes?

No he did not. I can ask Eric if it will make a difference. I have confirmed I do not have down pipe knock.

 

[SCOOBY DOO]

You're sucking the chip dry with the larger turbo. Get it reburned for the larger turbo.

 

[Pronto]

I would upgrade the injector harness with Casper's. You my be running into a resistance issue with old wiring.

 

[jshot]

You're sucking the chip dry with the larger turbo. Get it reburned for the larger turbo.

Eric Recommends updating the chip

 

[jshot]

OK Update time. i have the new chip installed. burned for the upgraded turbo. am now running 18psi boost with no knock. i have also tested at 17 pounds. i am seeing the mv still dropping but slower and not past 750 mv before it shifts.

this is good for knock, but does this sound normal for MV or should they lock in and hold ?

 

[Chuck Leeper]

What are the plugs telling you?
" i am seeing the mv still dropping but slower and not past 750 mv before it shifts".
Dropping from?

 

[Mr.Spool]

OK Update time. i have the new chip installed. burned for the upgraded turbo. am now running 18psi boost with no knock. i have also tested at 17 pounds. i am seeing the mv still dropping but slower and not past 750 mv before it shifts.

this is good for knock, but does this sound normal for MV or should they lock in and hold ?

750s is too lean
Your problem has not been fixed
Several in thread have given good ideas and your on the hunt.
I would check plugs send the fuel injectors out to be checked and flow the fuel lines and rail.
I have seen rust in the lines from age and sitting come off and lodge in the fuel injectors.
I would also suggest installing a wideband o2 and seeing what the real afr actually is.

 

[jshot]

What are the plugs telling you?
" i am seeing the mv still dropping but slower and not past 750 mv before it shifts".
Dropping from?

Hard to tell with the slow scan time of the scanmaster. probably 780-800. i have not tried adding fuel to this chip.
i will pull the plugs and post some pics as I do not know how to read them. may take a few days...i will try and get at it.

the car goes into storage next week so may have to flow test the injectors next season.