[rcoe]

Thought I had it beat.

Friday fired it up put 30 miles on it and it ran real good, still seemed like it had a slight miss at and just off idle. But unless you were looking for it you might miss it. Even got on it a bit and when on the gas felt great.

Fired it up on Sunday evening and it was greeted with a very poor idle.

No vacuum or exhaust leaks, no codes.

[laynlo15]

I'm sure you have already checked the plugs and wires. If you have one that's bad, you can have intermittent misfires. I've had that happen when I built a motor for my 16ss, didn't figure it out till we put in on the dyno and had a broken plug wire. Made up a new wire and put it on while on the dyno and that fixed it.

[rcoe]

Originally Posted by laynlo15

I'm sure you have already checked the plugs and wires. If you have one that's bad, you can have intermittent misfires. I've had that happen when I built a motor for my 16ss, didn't figure it out till we put in on the dyno and had a broken plug wire. Made up a new wire and put it on while on the dyno and that fixed it.

That is the plan for this morning, putting the stock wires that I took off last year back on. Was nothing wrong with them just did the MSDs when I swapped valve covers.

Maybe I'll get lucky.

[Katech_Mike]

Originally Posted by rcoe

That is the plan for this morning, putting the stock wires that I took off last year back on. Was nothing wrong with them just did the MSDs when I swapped valve covers.

Maybe I'll get lucky.

MSD wires are extremely low quality these days.

We have seen them cause issues more than a few times.

[rcoe]

Originally Posted by Katech_Mike

MSD wires are extremely low quality these days.

We have seen them cause issues more than a few times.

Might have to pick up a set of your long ones soon.

But after pulling all the plugs, all looked good, and reinstalling the OE wires still the exact same. Very rough idle, very lean and at times will almost die just sitting there.

[Kamero6]

Check exahaust header temp for each cyl. That test tells you everything.

[rcoe]

Originally Posted by Kamero6

Check exahaust header temp for each cyl. That test tells you everything.

Just use a temp gun once it is warmed up a little? I am thinking I should be looking for a temp variation between the cylinders?

[rcoe]

Not easy to get an accurate reading and it bounces around quite a bit, very dependent on location. Seems the sweet spot is a couple inches down the tube.

Once warmed up most stayed in the 360 to 400 range, #2 seemed lower but I could not get lower on the tube and the same with #7 this one never gave me a reading of over 300.

I am going to put it in the air tomorrow, might be easier from underneath.

[laynlo15]

Could be an injector or coil. Are you tuning the car or just logging and someone else is tuning it?

[KingLT1]

Originally Posted by laynlo15

Could be an injector or coil. Are you tuning the car or just logging and someone else is tuning it?

Car was originally built and tuned by Strictly performance. I did a flex fuel tune on it last fall and it was running great. Rcoe made some changes to setup over winter and it's been intermittently acting strange since this spring. The o2's sensors were not switching properly. He fixed that and the logs look ok from what I can see. He also changed intake tube diameter to 4" so maf needed rescaled. But other then that I didn't see anything abnormal. Fuel trims looked fine, fuel pressures good, no misfires...timing is where it should be. Last time we spoke he took it to a road course event and said it ran great.

Now that I think about it I wonder if it's something maf related. As in it's producing poor resolution due to placement and going to the larger intake tube? I know some others ran into issues before with poor maf placement causing issues at idle, but those were F1a94 C7 kits.

[Kamero6]

Originally Posted by rcoe

Just use a temp gun once it is warmed up a little? I am thinking I should be looking for a temp variation between the cylinders?

Yep, Keep checking every minute, starting with a cold engine. Some problems show up after warming up.

All cylinders should have roughly the same temp. You can even go for a drive, step on it and check again.

[Kamero6]

Originally Posted by rcoe

Not easy to get an accurate reading and it bounces around quite a bit, very dependent on location. Seems the sweet spot is a couple inches down the tube.

Once warmed up most stayed in the 360 to 400 range, #2 seemed lower but I could not get lower on the tube and the same with #7 this one never gave me a reading of over 300.

I am going to put it in the air tomorrow, might be easier from underneath.

Check the range of you temp gun. The best ones are the Flir with thermal image. They are expensive but worth it.

If 2 and 7 give you lower readings dig into that a little bit more.

[CamOnlyJabroni]

Originally Posted by KingLT1

Car was originally built and tuned by Strictly performance. I did a flex fuel tune on it last fall and it was running great. Rcoe made some changes to setup over winter and it's been intermittently acting strange since this spring. The o2's sensors were not switching properly. He fixed that and the logs look ok from what I can see. He also changed intake tube diameter to 4" so maf needed rescaled. But other then that I didn't see anything abnormal. Fuel trims looked fine, fuel pressures good, no misfires...timing is where it should be. Last time we spoke he took it to a road course event and said it ran great.

Now that I think about it I wonder if it's something maf related. As in it's producing poor resolution due to placement and going to the larger intake tube? I know some others ran into issues before with poor maf placement causing issues at idle, but those were F1a94 C7 kits.

I wonder if it's going lean with poor idle it's getting air in front of the MAF it doesn't know about?

[KingLT1]

Originally Posted by CamOnlyJabroni

I wonder if it's going lean with poor idle it's getting air in front of the MAF it doesn't know about?

I haven't seen any idle logs since he fixed the o2's, but if it was going lean from unmetered air entering the system then the fuel trims would go extremely positive.