View Poll Results: what should fix this
replace the factory O2 sensor
0
0%
more tuning on the MAFterburner
0
0%
make sure the MAFterburner gets an RPM signal
0
0%
check TPS voltages
0
0%
something else?
1
100.00%
Voters: 1. You may not vote on this poll
EDIT: HELP post 11, now my car won't start. Poor Part Throttle running (when running)
05-21-2008, 06:43 PM
#1
Three Wheelin'
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Good Idle, Good under load, Bad Part Throttle
I'm trying to figure out why my car idles at a nice 14.7-14.9 and runs great under load but when I just start to give it gas it goes lean (16:1-18:1) and stumbles.
This problem didn't exist before switching to a MAF system, and doesn't seem to happen every time (I think it's worse when the engine is cold). Sometimes when I've been driving around and return to idle it will be rich and then slowly work it's way back to 14.7
What should the TPS voltage be with the throttle closed? The voltage should increase at a linear rate w/ relation to the throttle position?
This is what I'm scratching my head over so far:
This problem didn't exist before switching to a MAF system, and doesn't seem to happen every time (I think it's worse when the engine is cold). Sometimes when I've been driving around and return to idle it will be rich and then slowly work it's way back to 14.7
What should the TPS voltage be with the throttle closed? The voltage should increase at a linear rate w/ relation to the throttle position?
This is what I'm scratching my head over so far:
If it was an electrical issue or faulty reading of the wideband, your reading would be inconsistent. If it is ALWAYS high off boost and then drops back down to where it belongs only at WOT as you described ... then it is more likely that the wideband is reading correctly and showing you something is wrong. Especially if you were previously getting typical readings and only recently started to see the issue.
It is going into closed loop mode at WOT and ignoring the signal from the O2 sensor, thats why it makes sense that it is the narrowband O2 sensor.
It is going into closed loop mode at WOT and ignoring the signal from the O2 sensor, thats why it makes sense that it is the narrowband O2 sensor.
From Clark's Garage:
When the DME is operating based on the feedback signal from the O2 sensor, this is referred to as Closed Loop operation. If the O2 sensor is faulty or is disconnected, the DME computer operates in Open Loop mode. In this case, the DME simply proves the fuel by determining the amount of air flow into the engine and selecting the appropriate amount of fuel from a set of preset fuel maps. On 944s which do not have O2 sensors (many ROW cars), the DME operates in Open Loop mode from preset fuel maps.
When the DME is operating based on the feedback signal from the O2 sensor, this is referred to as Closed Loop operation. If the O2 sensor is faulty or is disconnected, the DME computer operates in Open Loop mode. In this case, the DME simply proves the fuel by determining the amount of air flow into the engine and selecting the appropriate amount of fuel from a set of preset fuel maps. On 944s which do not have O2 sensors (many ROW cars), the DME operates in Open Loop mode from preset fuel maps.
Last edited by porschefig; 05-29-2008 at 08:16 PM.
05-21-2008, 06:57 PM
#2
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Can you post a pic of your MAF? Just wondering where your actual sensor is. If it's one of the MAFs that has the sensor just past the elbow, the sensor needs to be clocked around the 10 o'clock position. I don't think the newer ones have this issue, since they're in the straight part of the tube.
http://www.arnnworx.com/tps-repair.htm
http://www.arnnworx.com/tps-repair.htm
05-21-2008, 07:16 PM
#4
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What MAF system do you have? Are you converting an MAF signal to read like an AFM?
On a related note, GotMeAPorsha will be in great falls next week and he may be able to help you out since he's MAF equipped and dealt with some of his own stumbling issues sucessfully.
On a related note, GotMeAPorsha will be in great falls next week and he may be able to help you out since he's MAF equipped and dealt with some of his own stumbling issues sucessfully.
05-21-2008, 07:38 PM
#5
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Yes, I'm using a piggy back to convert the MAF signal.
Here's the set up I have, I could be forgetting some things.
LR MAF
MAFterburner
951MAX chips
Stock injectors
3bar FPR
Tial Wastegate (38mm, I think) using the dual port capability
MBC set to 15 psi max
Venturi delete, Cycling valve delete
Zeitronix zt-2
NO catalytic converters
Otherwise stock 2.5" exhaust except PO installed ANSA cat-back
Sadly, I won't be in Great Falls next week, I'm rarely ever there anymore (should change location on Bozeman, MT). But thanks for the heads-up! (what would anyone want to be in Great Falls for? ROFL)
Here's the set up I have, I could be forgetting some things.
LR MAF
MAFterburner
951MAX chips
Stock injectors
3bar FPR
Tial Wastegate (38mm, I think) using the dual port capability
MBC set to 15 psi max
Venturi delete, Cycling valve delete
Zeitronix zt-2
NO catalytic converters
Otherwise stock 2.5" exhaust except PO installed ANSA cat-back
Sadly, I won't be in Great Falls next week, I'm rarely ever there anymore (should change location on Bozeman, MT). But thanks for the heads-up! (what would anyone want to be in Great Falls for? ROFL)
05-22-2008, 02:50 AM
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If you are running an AFM chip with the Lindsey MAF you need to add fuel at the idle to part throttle transition. The behaviour of these two sensors are quite different in this area.
05-22-2008, 05:56 PM
#7
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Ok, that could be it. Any other 951MAX chip users with this problem? I've been told by Russell that my chip is a MAF chip (adjusted for more air flow vs. the AFM) but not a TRUE MAF chip (that doesn't need a piggy back to work with a MAF).... I've adjusted it to nearly 100% rich for the voltages to the right of where my car idles, still goes lean at that idle to part throttle transistion.
I need a nice day to spend tuning....
I need a nice day to spend tuning....
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05-23-2008, 12:50 AM
#8
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Check with Russell to see what injectors and FPR the chips are programmed for.
I had that same lean partial throttle issue when my car was a 2.5 with stock injectors, APE MAF, 3bar FPR, with both APE and pre-Russell LR chips. It helped to have an Adjustable Fuel Pressure Regulator to set a pressure that keeps the needed MafterBurner adjustment within the capabilities of the MafterBurner's adjustment range. I had a Super61 turbo so I had to up my injectors to 48#.
I had that same lean partial throttle issue when my car was a 2.5 with stock injectors, APE MAF, 3bar FPR, with both APE and pre-Russell LR chips. It helped to have an Adjustable Fuel Pressure Regulator to set a pressure that keeps the needed MafterBurner adjustment within the capabilities of the MafterBurner's adjustment range. I had a Super61 turbo so I had to up my injectors to 48#.
05-24-2008, 11:20 PM
#9
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I just sent Russell an email but I think the chip is written for my set up from reading over our previous emails.
One person voted in the poll for "something else" I'm curious what that person thinks?
I'm going to try tuning with the factory O2 sensor disconnected unless that's a bad idea...
One person voted in the poll for "something else" I'm curious what that person thinks?
I'm going to try tuning with the factory O2 sensor disconnected unless that's a bad idea...
05-27-2008, 07:27 PM
#10
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The Lindsey Racing's MAF installation instructions say to get an RPM signal from DME pin #1.
Tom M'Guinness' very helpful website says to get an RPM signal from DME pin #21 for Zietronix datalogging.
Which is right, Rennlisters?
EDIT: Follow the directions and use DME pin #1
My car didn't wouldn't start when I tried to get the RPM signal from DME pin #21
Tom M'Guinness' very helpful website says to get an RPM signal from DME pin #21 for Zietronix datalogging.
Which is right, Rennlisters?
EDIT: Follow the directions and use DME pin #1
My car didn't wouldn't start when I tried to get the RPM signal from DME pin #21
Last edited by porschefig; 05-31-2008 at 12:20 AM.
05-30-2008, 06:53 PM
#11
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Here's a datalog of me revving the car from idle and then letting off the gas. Car is parked, not driving around... that's all I've had time for since getting it to read rpm's but this gives a good idea of what its doing.
I made the cells orange after it started going lean, and red where I let off the gas (as judged by rpms, but looking at TPS position I let off just a bit before revs started to fall).
I made the cells orange after it started going lean, and red where I let off the gas (as judged by rpms, but looking at TPS position I let off just a bit before revs started to fall).
Last edited by porschefig; 05-31-2008 at 12:21 AM.
