Intermittant miss at light load cruising only

[Blazer406]

I got the injectors and chip swapped out and did a little driving. It acted pretty good....but didn't have a chance to get it out on the interstate....... runs pretty good when mashed. It puts a big grin on my face anyway......:biggrin:

I have to travel out for work, so I might not get a chance until next weekend to get to drive it some more......

 

[Blazer406]

I've put several hundred miles on it since I put the new injectors in.....car runs good except for the stumble...... I did datalog it. At first glance.....nothing stands out immediatly....except the little stumble appears to be a lean spike just after you take off at light throttle.

Check datalog @ frame 351 - frame 358

The only odd thing is this is the 2-3 frames leading up to when it goes into closed loop.

This is where I think the stumble is. I will say this particular time....it wasn't as bad as it sometimes is (the stumble) but it is still there.

Any ideas?

 

[TurboBuRick]

Did you try running in batch fire?

RL

 

[Blazer406]

Did you try running in batch fire?

RL

I forgot to try that yet..... I will give that a try.... maybe tomorrow if I bring the car to work.

I am hoping someone might notice something in the datalog that I might have missed.

 

[Eric Stage I]

The bigger the injector, the more sensitive it is to fuel pressure and how it affects the AE pump shot. The stumble could either be that it's slightly rich or slightly lean. I would try adjusting the fuel pressure say 4psi higher, then 4psi lower, and see which way is better with the stumble.

Other causes could be cam sensor related, as Rick pointed out, and also MAF related. But if it didn't stumble with the old injectors, then I suspect those items are ok.
Eric

 

[Blazer406]

The bigger the injector, the more sensitive it is to fuel pressure and how it affects the AE pump shot. The stumble could either be that it's slightly rich or slightly lean. I would try adjusting the fuel pressure say 4psi higher, then 4psi lower, and see which way is better with the stumble.

Other causes could be cam sensor related, as Rick pointed out, and also MAF related. But if it didn't stumble with the old injectors, then I suspect those items are ok.
Eric

I will give it a try when I have a chance to mess with it some more. It might be this weekend though.

Just watching the wideband real time, I think it spikes lean when it stumbles. It is very repeatable when you are just easing away from a stop light.

I did advance my cam sensor just a touch when I installed it. I might should have advanced it just a little more. I was using a chart to tell me where to put my line on the flywheel.......

http://www.gnttype.org/techarea/ecmsensors/camsensor.html

This is the procedure I used.... and I did it at 23° ATDC instead of 25° ATDC..... so in theory.... it is advanced 2° from the factory spec. Some say it makes no difference.... I'm not sure if it does or not. I will add that I used a homemade led cam sensor tool that should function just like the caspers tool when I used this feature.

I'll try and get a datalog where it stumbles more pronounced..... and also try it with the FP adjusted like you said Eric.

I'll also crank it and unhook the cam sensor forcing it to run in batch fire mode and see if that has any effect. If it does, the cam sensor itself or cam sensor adjustment is hosed up.

 

[Blazer406]

Well.... before I left this morning for work, I hooked up my FP gauge..... jumped the FP out..... and the gauge read between 41 and 42 psi. I bumped it to 45 psi. I drove it to work..... forgot my laptop, so I cannot log it today :-(

Well... it still stumbles..... can't tell if it is much better.... will try and log it again later. I will also try the cam sensor unhooking as well. I may try it on the way home.

On a positive note.....filled up this morning and checked mileage...... I got 19 MPG..... didn't romp on it a whole lot on this tank..... burned up about 1/2 the tank of alky...... so it was driven....