944 turbo running rich under boost

[superbad_austin]

I purchased a 944 turbo track car in November to use in addition to my NA 944 24 hours of lemons race car. The car has an older build on it with a pretty extensive Kokeln build. The engine and turbo were subsequently rebuilt using an Evergreen K26/27 hybrid. When I bought the car it hadn't been on track for about 2 years.

When I got the car it was running lean under boost, staying in the 12-13 AFR which caused me to do a heavy refresh on the fuel system. This included a new fuel filter, a new adjustable FPR to replace the old one which didn't build pressure with boost, and having the injectors cleaned and flow tested. Once I got that work all completed the car now runs rich with AFRs in the low 10s under boost. The car had an old AFR which I could no longer get the wideband O2 sensor for so that was replaced with a new gauge and sensor.

I've gone through and tested the AFM barndoor to verify that the resistive range is correct, replaced the cylinder head temp sensor, the DME relay, the throttle position sensor, and smoke tested the front end. The car originally had the wideband O2 in the factory bung so the engine management was running open loop.

The car has the original Bosch ECU with an unknown chip in it.

I had the car at our local Porsche specialist in Austin who verified most of my work and they haven't been able to find any root cause. Since I have an unknown provenance on the ECU chip and the original harness the suggestion is to migrate to a modern ECU with a new harness to have a known baseline.

What is concerning to me is that this configuration of injectors, FPR, and tune should have been running acceptably. So I'm not sure what has changed or where to debug next. The FPR is set to about 43psi with the vacuum hose removed and I have verified that it goes up 1:1 with pressure when I put a pump on the vacuum port of the FPR. The injectors are Bosch 0 280 150 803, ~35 lb/hr, all flow-matched to 368 cc/min, I had them cleaned and tested.

I am trying to make it to 944fest at the end of August and I'm not sure where to go next on my diagnostics.

I have a RaceCapture datalogger for the lemons 944 so I could measure fuel pressure and boost pressure along with the AFM signal at the ECU. The garage checked the AFM measurement at the ECU and said it looked normal.

So my questions to the Porsche community here are two fold:

1) Any ideas where to go next on the debug?
2) If I were to track it with AFRs in the 10s under boost am I running the risk of washing the cylinder walls and damaging the cylinders?

Long term I think the right approach is to swap to the MaxxECU setup but I doubt I could make that happen before 944Fest.

Thanks in advance for any collective wisdom.

[Tom]

I purchased a 944 turbo track car in November to use in addition to my NA 944 24 hours of lemons race car. The car has an older build on it with a pretty extensive Kokeln build. The engine and turbo were subsequently rebuilt using an Evergreen K26/27 hybrid. When I bought the car it hadn't been on track for about 2 years.

When I got the car it was running lean under boost, staying in the 12-13 AFR which caused me to do a heavy refresh on the fuel system. This included a new fuel filter, a new adjustable FPR to replace the old one which didn't build pressure with boost, and having the injectors cleaned and flow tested. Once I got that work all completed the car now runs rich with AFRs in the low 10s under boost. The car had an old AFR which I could no longer get the wideband O2 sensor for so that was replaced with a new gauge and sensor.

I've gone through and tested the AFM barndoor to verify that the resistive range is correct, replaced the cylinder head temp sensor, the DME relay, the throttle position sensor, and smoke tested the front end. The car originally had the wideband O2 in the factory bung so the engine management was running open loop.

The car has the original Bosch ECU with an unknown chip in it.

I had the car at our local Porsche specialist in Austin who verified most of my work and they haven't been able to find any root cause. Since I have an unknown provenance on the ECU chip and the original harness the suggestion is to migrate to a modern ECU with a new harness to have a known baseline.

What is concerning to me is that this configuration of injectors, FPR, and tune should have been running acceptably. So I'm not sure what has changed or where to debug next. The FPR is set to about 43psi with the vacuum hose removed and I have verified that it goes up 1:1 with pressure when I put a pump on the vacuum port of the FPR. The injectors are Bosch 0 280 150 803, ~35 lb/hr, all flow-matched to 368 cc/min, I had them cleaned and tested.

I am trying to make it to 944fest at the end of August and I'm not sure where to go next on my diagnostics.

I have a RaceCapture datalogger for the lemons 944 so I could measure fuel pressure and boost pressure along with the AFM signal at the ECU. The garage checked the AFM measurement at the ECU and said it looked normal.

So my questions to the Porsche community here are two fold:

1) Any ideas where to go next on the debug?
2) If I were to track it with AFRs in the 10s under boost am I running the risk of washing the cylinder walls and damaging the cylinders?

Long term I think the right approach is to swap to the MaxxECU setup but I doubt I could make that happen before 944Fest.

Thanks in advance for any collective wisdom.

Welcome to Carpokes!

Personally, I wouldn’t rush to install and tune a standalone before the Fest. There’s too much to dial in and get right in a month, and I strongly suspect you can correct the AFRs more quickly by sorting out what you already have. I’d want to get them into the mid-to-high 11s before the Fest. Plenty of cars survive in the high 10s, but there’s no reason to risk it.

How much boost are you running?

Do you have a known-working wideband, and can you post a log of a WOT run?

Do you have the factory narrowband O2 sensor installed in the stock location? If so, is the car entering closed loop and consistently centering around 14.7:1 at idle and during steady cruising?

You are running unknown chips, so you really have to start there. Without knowing what they were mapped for—2.5-bar FPR, 3-bar FPR, stock turbo, huge turbo, etc--you have no basis for assuming the combination should run acceptably. A specialist who can’t find the cause of excessive richness without first verifying the chip isn’t being especially special.

A 3-bar FPR is a sensible choice with that turbo if you’re running the typical 14–15 psi, but the chip needs to be mapped for it. If your chip was designed for a 2.5-bar regulator, switching to 3 bar increases fuel flow by about 9.5%, which alone could easily push the AFRs into the 10s.

Even if the chip was designed for a 3-bar FPR, a surprising number of 3-bar chips go excessively rich above roughly 5,000 rpm because of the counterintuitive way fueling-map changes can affec --or sometimes fail to affec-- AFR under certain conditions.

We have an extensive chip-tuning guide here on Carpokes. If it were my car, I’d start by reading the chip and opening the image in TunerPro. My guess is that it’s either mapped for a 2.5-bar FPR and is now over-fueling by about 9.5%, or it’s mapped for 3 bar but has fuel maps that are ineffective at pulling fuel in the upper-rpm range.

You can get a chip reader/programmer from Amazon in a couple of days, and TunerPro is a free download. With those, you can pull the image from the chip and see what is actually going on in there. I can help too as needed...

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[superbad_austin]

Thanks for the quick response.

The boost seems to be capped at 15psi but I am relying on eyeballing the gauge and what the previous owner told me. He said he dialed it down from 18-20psi a few seasons prior.

As the car was running a 3bar adjustable regulator when I bought it, I just swapped like for like. Reading the EEPROM seems like the best next step.

I am planning to instrument the car next weekend to read fuel pressure, boost, and AFR with the race capture box so I am not trying to eyeball it while doing a pull under boost.

I appreciate the feedback and will let you know once I get my hands on the actual EEPROM content.