Intermittent Rough Running Diagnosis

[tony-baroni]

I have a 350 chevy small block, TBI motor. In a G-30 van, 1995 model. The engine is a crate GM truck motor, with summit AL heads, roller cam (stock truck cam), rebuilt TBI, upgraded fuel pump, new distributor and all the tune up stuf when it was built. Maybe 20k on the rebuild. It is running a programmed chip from harris. Lots of new stuff on this one, it's been running fairly well for a while, but I recently started having trouble.


The trouble started in Southern California, after filling up at Costco, I had a lot of stumbles on the highway. Took it easy, switched to Chevron gas. It got better, kept getting smoother after multiple tanks of new gas, as we drove it back to Northern California.

Then another road trip, to Oregon border, broke down with a power steering pump, took some time to get that fixed, and drove back home. It had the minor stumbles throughout the trip, but nothing to write home about.
Then it sat parked for 3 weeks or so.

The next drive, was a 75 mile drive, and it ran like crap the first hour, really shuddering stumbles, and it had no power under WOT. It even struggled to raise the RPms and reach highway speeds on uphill sections. Then after about an hour it ran normally. Drove a bit around for a day or two, then drove the 75 miles back home. Intermittent mild stumbles coming back home. It sat another 3 weeks or so.

Yesterday I drove it locally, and it was really bad, shaking the van again with the stumbles. Short trips, but it was worrisome.

Today I got my ALDL cable out, and PC loaded with TunerPro again, and monitored it while it was running, and some short 1 mile drives. It was back to the mild stumbles.

I was able cause some bad shudders by holding down the gas while parked in drive with my foot on the brake. I recorded that in TunerPro.

I did see that the system is adding knock retard during that shuddering time.

Could someone take a look at the file and let me know if they see any possible items to dig into? I am new to this, and am not sure where to look first. And I don't know if the numbers are what they should be anyway! :-0

[sturgillbd]

You didn't get your datalog to attach to your post. Have you checked fuel pressure? Have you inspected your distributor cap and rotor? There are lots of things that can cause the shuddering and loss of power. Post your datalog and a copy of your bin if you have a way to read the chip.

[tony-baroni]

Thanks Sturgillbd

I did a visual inspection of the wires, and cap (without taking it off). Everything looked good. Then inspected fuel injectors with the key on, and then idling, and then just a little gas, it seemed fine.

Then I checked the fuel pressure, and it was too low. Figured a bad regulator, took that out, and found the adjustable set screw that holds the regulator in place was fully backed out. It must have backed itself out from vibration.

I'll have to get on my PC to upload a log and bin....now I'm focused on figuring out what I can put on those threads to prevent that from backing out again, that won't fall apart in the fuel and clog up the injectors, any ideas?

You didn't get your datalog to attach to your post. Have you checked fuel pressure? Have you inspected your distributor cap and rotor? There are lots of things that can cause the shuddering and loss of power. Post your datalog and a copy of your bin if you have a way to read the chip.

[sturgillbd]

If its a stock style regulator, the threads shouldn't be exposed to fuel. You could use some light duty loctite on the threads of the adjustment screw.

[tony-baroni]

Thanks for pointing that out, I have since learned more about this unit. It's been sent back to the guy who sold it to me, he adjusted it and confirmed the adjustable fuel pressure regulator was good.
I have set the FP to 15psi, and put the stock memcal back into it. That hasn't helped at all, I have to check timing next.
What do you think about the state of the distributor cap and rotor? This is with about 10k miles on it.
IMG_0161.jpg
IMG_0160.jpg

[tony-baroni]

Okay here's another update. It's idling high, around 1900. The TPS voltage with throttle closed is 0.6V. The TBI is whistling very loudly, a piercing whistle, when the throttle is closed. I was able to make a log file, starting it from nearly cold, getting it to closed loop mode was possible while idling because of the high idle. Then drove it, but tried driving it without giving it any gas really. Then turned around and drove it a bit with around 15% throttle. The driving starts around 6m mark on the log.

I hope the file upload worked properly. The bin is a custom one, based on BNKM, and I am using a definition file for $31.

How can I get the idle down to where it should be?
Is it normal for the knock retard to stay so consistently around 6 deg?


Other items, I checked manifold vacuum and it's in the green around 21 in Mg on my gage with this high idle. When I put it in gear, the idle drops, and then it shows in the red zone, indicating late ignition timing, only around 15 in Hg Vac