Turbo 4.3L Tuning and Misfire Diagnosis

I put a turbo on my 4.3L, upgraded to a marine intake with 42 lb injectors and upgraded to a high flow fuel pump. I have flashed the injector calibration and tuned for the turbo by adjusting the power enrichment table.


I have it running fairly well except once the engine is warmed up and I am cruising at low RPM the engine will misfire. It will stop if I completely back off the throttle or open it up. I am wondering what I can monitor on the VCM Scanner to help me diagnose the cause of the misfire. My plugs, wires, coil and distributor are almost brand new along with the injectors so I don't think it is them but I want to be safe. Another thought I had was the cross over pipe for the exhaust manifold runs near the crank sensor so I am wondering if heat from exhaust is causing it to malfunction.

Or maybe I need to adjust other tables because of the addition of the turbo and that will fix it?


I am fairly new to tuning so any help/advice is greatly appreciated.

First lesson here. Power enrichment is a set and forget table, if you didn't know that already. The idea is to pick a value you wish to run under boost. Say you want to run 11.0 AFR, that is the value you set in there and you never change it again.

The airflow model is how you adjust the fueling. Those being the MAF curve and the the VE table. The higher the values get in those tables, the more fuel it adds and if you remove from those tables, it removes fuel.

A wideband o2 sensor is a 100% must for tuning and you must buy one if you don't already have one.

Without the tune file and data logs we can't see what you have done. But hopefully you've taken the proper steps to unsure you can data log for boost correctly with a 2 bar MAP sensor, good fuel pressure etc etc.

( I want to hope this is a newer P01 or P59 computer so using a 2 bar OS is possible as it will make tuning much easier)

Monitor Fuel trims and spark Knock Retard.

Chances are the air fuel ratio when cruising is way off, causing the missfire. Or the spark timing might be off.

Also the fuel trims might be off because the MAF readings are off because of the turbo.

Is the Money light ON and OBD codes ?

Quote:

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Originally Posted by Founman

I put a turbo on my 4.3L, upgraded to a marine intake with 42 lb injectors and upgraded to a high flow fuel pump. I have flashed the injector calibration and tuned for the turbo by adjusting the power enrichment table.


I have it running fairly well except once the engine is warmed up and I am cruising at low RPM the engine will misfire. It will stop if I completely back off the throttle or open it up. I am wondering what I can monitor on the VCM Scanner to help me diagnose the cause of the misfire. My plugs, wires, coil and distributor are almost brand new along with the injectors so I don't think it is them but I want to be safe. Another thought I had was the cross over pipe for the exhaust manifold runs near the crank sensor so I am wondering if heat from exhaust is causing it to malfunction.

Or maybe I need to adjust other tables because of the addition of the turbo and that will fix it?


I am fairly new to tuning so any help/advice is greatly appreciated.

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What did you set the spark plug gap to? What plugs are you running?

I am using TR6 plugs, gapped to 0.025". This was the recommended gap (0.025-0.028") on the Typhoon/Syclone forum, so I figured I'd follow suit. I also added an Accel coil, and that seemed to solve my misfire issues.

5fDP,

I have a wideband O2 and plan to log data off of the EGR circuit since it is no longer in use. I also recently discovered a problem with my MAF circuit (it is not reading airflow). I know it was reading it when I first stared having the issue but maybe it was on its way out. Either way I wasn't running a 2 bar map yet so I ordered one and it will be here later this week. Once it arrives I will attempt a speed density tune and get some good data logs to post along with my tune. I appreciate your willingness to look at them.

ZeroBoostBuick,

The AFR while cruising is fairly stable, oscillating around 14.7 as expected. I was suspecting spark may be an issue but I am not sure what to look for/adjust especially since the problem is happening with no boost. I have a P0300 random misfire and a P0102 Mass or Volume Air Flow A Circuit Low


Spooledyou08,


I have Bosch Iriduim plugs gapped to 0.026" with an accel coil as well.

Thanks everyone for the help.