So I recently installed a MAP v-band turbo kit with a Precision 5858 ball bearing turbo. I also installed a walbro 400lph fuel pump and ID1300cc injectors. Stock block and stock cams, currently running on 93. The car went to get tuned but my tuner had to leave me with a conservative map because of what seems to be a misfire. Under load, there is no evidence of it, it's only having trouble at idle. It idles steady and every few seconds, the rpms dip a bit and I hear a small "puff" from the the exhaust like it stutters. It does this at somewhat random intervals and I can't figure out the cause, no engine codes. I boost leak checked it and that's clear, as well as replaced the spark plugs. So at this point, I'm thinking it's fuel system related, either bad fuel pressure or a clogged injector. Any thoughts on this? Any other things that could be causing this? Is it actually a misfire? Maybe too much injector? So many questions, would appreciate any input.

 

What do the AFR's do when it does this?

 

Afr is steady but will jump to around 15.5-16 when the suspected misfires happen

 

If I were you I wouldn't run it until you figure out what it is. I blew my engine because of an injector related problem that gave symptoms very similar to yours. Can you pull the injectors to see if theres any clogs? Also when you installed the pump did you use corrugated tubing?

 

Wasn't planning on running it for that reason. What should I look for when pulling the injectors? And yes, the pump kit I bought included the corrugated tubing. It's the MAP pump installv kit

 

Its hard to test injectors without getting them flow tested, but do a quick visual check to make sure theres nothing in the fuel rail side of the injector, like gasket material or anything. Have you checked the spark plug gap and all that?

 

Yeah, they jump lean because there is a misfire. Did you make sure there are no exhaust leaks upstream of the O2 sensor?

 

I'll look for that. Just replaced the spark plugs, all were the same OEM gap. Should they be adjusted to a different gap than OEM?

 

Yup, did this along with the boost leak tests. Checked the manifold nuts and v band clamps for the turbo to manifold and downpipe to turbo. Let the car run and felt for any leaks, nothing.

 

Sparkplug gap should be .020". But that will effect WOT way before it effects idle.

 

WOT runs sooth, but understandably, my tuner was concerned about pushing the car with it misfiring at idle. If it were to start running lean and misfire on the dyno, it could've caused some damage. So unfortunately I'm stuck with a light tune and not driving the car until I can diagnose and fix the issue.

 

I suspect your misfire is being caused my something like bad idle settings. An ignition system related misfire, or even fuel system would only become worse with load. If AFR's are normal at idle, I would look into what the MAF is doing (log MAF Hz, make sure its smooth, and not jumping around), and if could also be one of the idle settings.


Who is the tuner? His response to the issue makes me think you need to find a new tuner.

 

That's a good point, hadn't considered MAF and idle settings. The tuner is Calvin Dotson in Dallas. He's really popular around here. I'll ask him about idle settings, obviously if he's not open minded about what could be wrong with the tune, then yes, a new tuner may be helpful.

 

Did you do a rewire when you installed in the walbro 400?

 

Yes the MAP kit I bought came with all the wiring and the relay needed. However I very well may have made a mistake, I'm not a professional by any means.