388bu

iTrader: (1)

We just finished up a 6.0 LQ4 swap into my buddies 63 Nova. We are using a stock truck harness/ECM that I reworked. I also did the tune on it, but it was mostly just a copy of my tune which is a wait4me tune. Motor is all stock except for headers. Stock return style truck intake with the regulator in the fuel rail and using a Walbro GL392 pump. (I think thats the p/n of the pump)

Motor runs great until you get above 40% throttle or so. It just holds back, doesnt miss, but its definitely not all there. Only code it is throwing at the moment is a high idle which I have no idea why.

I threw it into open loop for grins, no change. I am suspecting the problem is fuel related. Maybe a bad regulator or injectors...I dunno. The next step is to check fuel pressure under load and see what that is.

Any other ideas? Thanks in advance.

Dickie-311

iTrader: (1)

Your return line could be too small what size are you using ?

Old Geezer

iTrader: (3)

Dbw??

388bu

iTrader: (1)

Funny you mention the return line. We are using -6 return all the way back to the tank to the stock pickup tube. I assumed it was 3/8" without looking at it too much, but quickly found out it wasnt.(Too used to working on G-Body's I guess) Maybe its 5/16?

Lets put it this way, a piece of 3/8" steel fuel line will slide over the hard line coming out of the pickup. Which is what we did. We just welded 3/8 line over the line coming out of the pickup. Not the most elegant solution, but we were on a strict budget that we ended up blowing out of the water. haha

We had the tank sumped and are running -8 up to the front of the car then dropping down to -6 before the fuel rail.

One other thing I will mention that may or may not be related. When you first start it, the idle kicks up to around 1500 for about a good second and then settles down to where it should be for cold start up.

Yes, this is a DBW set up.

Thanks guys!

Dickie-311

iTrader: (1)

MY buddy went thru this he had -10 feed line and -6 return and the motor was cutting out after 1/2 throttle ended up needing -8 for a return line .problem fix , i didnt know this until last fridaynight , my fuel system is -10 feed and -6 return .. (because all aeromotive regulators are -6 return) once i get to take the car out on the road i'll see if i need to change my return line to -8 .

supershift67

iTrader: (1)

It sounds like the throttle body is closing like a rev limiter. I think ,but not positive that the throttle body closes at the rev limit instead of it acting like a rev limiter or msd style misfire rev limit. That is how mine acts and it is a 2007 lq4 with dbw.
Put a fuel pressure gauge on it and tape it to the windshieldwhen driving it around so you can watch your fuel pressure and see if it drops off when the car noses over. good luck.

deuce4935

iTrader: (2)

5/16 and 3/8 lines were what the factory used which is equivalent to the -8 & -6 so that doesnt appear to be the problem. It looks like theres something shorting on the dbw setup. Check the voltage at the dbw pedal and the injectors when the pedal is pressed.

Dickie-311

iTrader: (1)

wrong

5/16 = -4

3/8 = -6

1/2 = -8

Pop N Wood

iTrader: (1)

Wouldn't 5/16 be an AN 5?

AN 4 should be 4/16 = 1/4

I thought too small of a return line would cause problems at idle, not under load. Seems like the harder the motor is pulling the less fuel that gets dumped to the return line.

Go figure.

Old Geezer

iTrader: (3)

Restricting the return can make the engine go rich, not lean...

Datalog it, and see wtf the DBW is doing..

deuce4935

iTrader: (2)

My standard to metric conversion may have been off but 5/16 and 3/8 ARE DEFINITELY what the factory used and are more than capable of handling at least 500hp, and a 255lph pump, I know because I'm using it on my setup.

Again as a stated above check your voltage readings at the pedal, throttle , and injectors.

Pop N Wood

iTrader: (1)

Not trying to start an argument, just trying to understand. I can see where too small of a return line would not allow the regulator to maintain the proper pressure. But it should be worse at idle and only get better the more fuel the engine uses.

Right?

Old Geezer

iTrader: (3)

We R on the same page!
Idle would/could be worse than @ elevated rpm.
My test: If you can't lower the psi by at least 5 psi from desired setting, there's a problem.
As for line sizes... LOTS of turbo Buicks running stock lines at 3/8 and 5/16" OD, and making well over 500- 600 HP.
But, that's only a v-sicks!

As for the DBW, AIRC there is a throttle reduction introduced at shift..[abuse], I'd be looking to see, [ON THE DATALOGS], if there's something going on in that area...

garys 68

iTrader: (1)

What effect would leaving traction control enabled have?

00fxd

I belive that I am experiencing the same situation with my LQ4/dbw/muncie into my '65 Corvette. I feel like I am rockin' along til about 5k rpm and then it just kinda won't go anymore. I am just at the test driving/working out the bugs stage. I had considered fuel press issues but haven't tested yet - no gauge yet. I am using 3/8 supply and orig truck regulator 5/16 return.
Does an '03 have traction control - it definately feels like a traction control reaction. But I guess it can't be traction control, obviously I don't have wheel sensors. I do have a Vss.
"Check the voltage at the dbw pedal and the injectors when the pedal is pressed."
deuce, or anyone can you please elaborate what voltage to check for at the throttle body etc?
Thanks, Frank