Got my 6.0 running! But...

[skoffice]

It seems to have a flat spot off idle, or when you hit the throttle really quick it won't respond, almost dies. I've only driven it a half mile or so, but it's probably run and idled for over an hour. Throws no codes, it's a DBC, replaced TPS, O2's read .445 volts (is this right?), mild cam. I know that my fuel pressure is around 48 psi, it's in a weird spot so haven't gotten to turn it up yet. But any other ideas that might be the cause of this? I thought flat spots were for carburetors?

[Clyde65]

Check you fuel pressure, I was thinking it should be around 58PSI, the FP could answer your issue. it could be starving when you accelerate.

[BR3W CITY]

clogged fuel injector, Maf, how was it tuned?

[Custom 68]

Drive it for a few miles if you can and it is safe it might clear itself up, the computers seem to continue to learn. Even after that mine still had a little stumble my tuner added a little bit to "tip in" and helped a ton. It is kindof like an accelerator pump on a carborator. Anyway if it is still there it can be tuned out.

[skoffice]

58 on the fuel pressure? I thought 53 for some reason, maybe because a 3 almost looks like an 8 LOL like my eyes, even my memory isn't 20/20. New injectors, new MAF, tune was a mail order done by Howell and we haven't ever had issues with them before. Custom 68 I was thinking it might just need to learn itself with more driving, I need to get some miles on this thing. Hopefully I don't need to add more tip in though, because it is running RICH. You would think I were running alcohol haha

[skoffice]

Turned the fuel pressure up, no difference. Drove it on the trailer and up the street a bit when I got to the exhaust shop, still stumbles over itself

[BR3W CITY]

How does it rev once it gets past the dead spot? Are you able to see what the timing is (if you have a way to monitor it)

Vacuum leak? Kinda shooting in the dark, need some more info.

[skoffice]

It does alright past the dead spot in a free rev, but when I drove it today it just wanted to sputter/bog down rather than pick up and go up top. I can hook the scanner back up and check the timing. It read around 25 on the MAP sensor at idle, but I don't remember what timing was. I'm almost thinking of a vacuum leak too, I'm going to take a real close look at everything manifold related tomorrow and see if I missed anything..

[BR3W CITY]

hmm, that does re enforce the vaccum leak idea. Since the truck rail runs a vacuum-actuated reg, i can see a vacuum leak causing a variety of these symptoms.

[ls1nova71]

How long has the engine sat? How much have you driven it? I would try the easy things first, and just drive it. Sticky injectors will usually fix themselves after some time. Just a thought and it's free to try.
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[skoffice]

Everything is new so I don't think I have any component issues. I'm running aftermarket fuel rails with a professional products adjustable regulator. The regulator has a vacuum port on it but I have it capped, could this be my problem? Does it need the fuel pressure to fluxuate?

[ls1nova71]

Yes, that makes a difference! If it has a spot for a vacuum hose to attach to it, then it needs to be hooked to manifold vacuum.

[skoffice]

Dammit! Ok I'm going to try that next. I was told by someone that it wasn't necessary unless you were using forced induction. But maybe it's the other way around..

[softballnrd27]

That vacuum port is for boost reference and if I am not mistaken you shouldn't have to hook it up but I could be wrong. What is your fuel pressure at?

[skoffice]

It's now at 58 psi. That's what I thought too was for boost, but now I'm not sure haha

[Custom 68]

Well on the stock fuel pressure regulator the vaccumm hose so at idle i think the pressure is that 53 psi but under load or free rev the pressure goes to 58 or something likt that so I dont remember for sure. The regulator you have is probably the same way. I would hook it up and see what it does.
Like I said before mine did it only at a take off and it was not real bad but worse than it should be, now after a tweek or two it is super. I bet your tuner can make an adjustment for you.
One other think how did it do after the exhaust was on, could you have caused a rich situation with you O2 sensors?

[skoffice]

It didn't make a difference with the exhaust on. I called Howell and he said go ahead and turn the pressure up to as high as 65 so I did and that didn't change anything either. He told me to plug the scanner in and watch the O2 sensor readings at the bad spots. If the voltage is showing too lean or too rich. I have been waiting on my new hydroboost to arrive so I haven't been able to do this yet.

[skoffice]

Got the wideband on it yesterday, and it was showing VERY lean. I ended up cranking the fuel pressure all the way up to 90 psi and its running 10 times better now! I also fixed my idle issue. Unhooked a small vacuum port and it idles much nicer. So I either need to port that back into the intake, or drill a hole in the throttle blade. Now I guess I need to figure out how to get this thing tuned in to the injectors that I have so I can run the appropriate fuel pressure, I'm trying to make it up to Reno for Hot August Nights!