Need help - rough running

70SCJ · Jun 9, 2019

Built and camm’d motor at about 14psi. Car initially runs fine then will run very rough at cruise. A/f goes to 1.5ish (single sensor) and both fuel trims go to 0.0. Is this a bad O2 sensor or something different.
Any help appreciated. Thanks

Catmonkey · Jun 10, 2019

What are your cam specs, or which cams? When you say "initially" what do you mean? Cold start versus warmed up or after you load a tune? Has the car been logged and results reviewed by your tuner?

70SCJ · Jun 10, 2019

Catmonkey said:
What are your cam specs, or which cams? When you say "initially" what do you mean? Cold start versus warmed up or after you load a tune? Has the car been logged and results reviewed by your tuner?

Stage III cams (MMR) w/Low pressure by-pass valve, Cold start the car ran fine then once warm the above started happening.
Car has not been logged and sent to the tuner yet. I'm just relaying data I picked off of my Interceptor gauges. I was hoping to eliminate several possibilities before getting the tuner involved.
Thanks.

SCGallo2 · Jun 10, 2019

Sounds like cold start open loop fueling is fine, then once your engine warms up and PCM switches to closed loop fueling you start to have issues. Are you running leaded race fuel that can foul your narrowband O2 sensors in both banks? Your A/F ratio doesn't make sense... I didn't think AeroForce Interceptor could read lower than 10.0 (0V=10.0, 5V=19.99).

I would try datalogging short and long term fuel trims with a SCT X3/X4 to verify what you are seeing on your Interceptor gauges. You could also log AFR if you know how to connect your wideband to your device.

70SCJ · Jun 11, 2019

SCGallo2 said:
Sounds like cold start open loop fueling is fine, then once your engine warms up and PCM switches to closed loop fueling you start to have issues. Are you running leaded race fuel that can foul your narrowband O2 sensors in both banks? Your A/F ratio doesn't make sense... I didn't think AeroForce Interceptor could read lower than 10.0 (0V=10.0, 5V=19.99).

I would try datalogging short and long term fuel trims with a SCT X3/X4 to verify what you are seeing on your Interceptor gauges. You could also log AFR if you know how to connect your wideband to your device.

Sorry, the A/F ratio on the Interceptor was 11.5 ish not 1.5. Typing on my phone sucks.

No race fuel, only E85. **Update** Ran the car a little bit. Same thing, cold start worked ok then once warm the trims fluctuated from what I considered normal with normal A/F ratio to both at 0.0. Then both trims went to 0.0 and A/F went into the 11's again and stayed there. I have checked the fuel and it tested out at E88. I checked the plugs and they were wet.
The injectors were just cleaned and flowed 2 months ago so I didn't think it was that. Still looking for answers.

Mojo88 · Jun 11, 2019

Just stating the obvious, but have you checked for vacuum lines that may be disconnected or cracked? Also, my car was running like crap last Summer, so I quick-cleaned the MAF sensor (with proper cleaner), and it still ran rough, then I REALLY cleaned the MAF sensor (with like 10 good sprays) and the car has been running perfect.

69b302 · Jun 11, 2019

You should data log your open loop flag to ensure your issue is when it switches to closed loop. If your cams have lots of overlap, you will get lots of fuel into the exhaust throwing the O2s off.

70SCJ · Jun 11, 2019

Mojo88 said:
Just stating the obvious, but have you checked for vacuum lines that may be disconnected or cracked? Also, my car was running like crap last Summer, so I quick-cleaned the MAF sensor (with proper cleaner), and it still ran rough, then I REALLY cleaned the MAF sensor (with like 10 good sprays) and the car has been running perfect.

I have checked the vacuum lines. They all looked good. My vacuum shown on the Interceptor is pretty consistent from what I had before this issue came up. I'll put the MAF on list of things to check out though, thanks.

69b302 said:
You should data log your open loop flag to ensure your issue is when it switches to closed loop. If your cams have lots of overlap, you will get lots of fuel into the exhaust throwing the O2s off.

What PID's would one look at for this? Asking for a friend.

Catmonkey · Jun 11, 2019

Stoich for e85 is 9.8:1, so it would appear to be a bit lean. Have you gotten a tune for this "built" engine? Which fuel trims are you looking at short term or long term? Ideally, the short term trims should be 0. I'm not sure how the Interceptor displays long term trims.

69b302 · Jun 11, 2019

I beleive the PID is just "open loop flag". What year GT500 do you have? The open/close loop tuning does not exist in the newer models(2011+ IIRC). The wideband is most likely reading lamba, and then converting to AFR, so is baiscally showing gas AFRs for ethonal fuel. I just let my wideband display lamba, as when using different fuels, lamba is consistent.

70SCJ · Jun 11, 2019

Catmonkey said:
Stoich for e85 is 9.8:1, so it would appear to be a bit lean. Have you gotten a tune for this "built" engine? Which fuel trims are you looking at short term or long term? Ideally, the short term trims should be 0. I'm not sure how the Interceptor displays long term trims.

Interceptor is set up to convert lambda to gas scale so the 11.5 is rich.
The engine was tuned by a national tuner a few years ago and has run well for quite awhile. Looking at short term trims for sure.

69b302 said:
I beleive the PID is just "open loop flag". What year GT500 do you have? The open/close loop tuning does not exist in the newer models(2011+ IIRC). The wideband is most likely reading lamba, and then converting to AFR, so is baiscally showing gas AFRs for ethonal fuel. I just let my wideband display lamba, as when using different fuels, lamba is consistent.

2007 car.

SCGallo2 · Jun 12, 2019

This morning, I set up my AeroForce Interceptor to read short and long term fuel trims on bank 1 (93 octane street tune). At normal operating temp and after about a minute of idling with A/F @ 14.7ish, Short Trim B1 and Long Trim B1 both settled on 0.0

69b302 · Jun 12, 2019

Most likely the oxygen sensors going south. I have had to replace the Motorcraft O2s every year or two on Ethanol. I am trying NTK sensors for the last year. Should eventually throw a code if it is really rough. I would also take a look at the fuel rail pressure on the interceptor gauge to ensure it’s not on the fuel side.

70SCJ · Jun 12, 2019

69b302 said:
Most likely the oxygen sensors going south. I have had to replace the Motorcraft O2s every year or two on Ethanol. I am trying NTK sensors for the last year. Should eventually throw a code if it is really rough. I would also take a look at the fuel rail pressure on the interceptor gauge to ensure it’s not on the fuel side.

I went ahead an ordered a couple of oxygen sensors from the local dealer. After talking with a shop that has done some work on my car before. Their first thought was the O2 sensors. I still have the originals on the car and the odometer is at 94K with about 30K on and off of E85.
The rail pressure is pretty rock steady at 44psi +-1.
Thanks everyone, I'll report back after I change out the O2's.

Need help - rough running

70SCJ

(Ret) USMC F/A-18 Driver

Catmonkey

I Void Warranties!

70SCJ

(Ret) USMC F/A-18 Driver

SCGallo2

Balanced performance

70SCJ

(Ret) USMC F/A-18 Driver

Mojo88

"Hammer" Time

69b302

Active Member

70SCJ

(Ret) USMC F/A-18 Driver

Catmonkey

I Void Warranties!

69b302

Active Member

70SCJ

(Ret) USMC F/A-18 Driver

SCGallo2

Balanced performance

69b302

Active Member

70SCJ

(Ret) USMC F/A-18 Driver

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