Ls help one more time, please!!!

[JJAB]

Guys I originally posted that I had a totally rebuilt 2000 6.0 LS that would not crank for more than 2 to 3 seconds. Well, this site came through for me because you all suggested that the tuner forgot to remove the VATS. This was true, he did!!

New issue, after re-sending the PCM to the tuner twice I am still experiencing this:

I do have the hot cam installed 218/228 DUR @ .050, .550/550 LIFT @ .050

First, I have to press the gas to crank the motor. Once the motor is running, it idles very low from time to time. Also, while its running, if I accelerate the motor, when it comes off of the acceleration, it dies or idles very close to idling and sometimes picks up to normal idle.

I was thinking that maybe the fuel pressure regulator is not operating correctly. But my first mind is telling me that the guy who tuned my PCM did not compensate for the cam that I have installed.

A little more info:

I have an original 1987 saddle tank installed with the EP381 corvette fuel pump installed flowing through the regulator located on the intake.

HELP GUYS!!!!

[BR3W CITY]

You should be able to check the fuel pressure with the valve on the rail, see if it falls off, or if your maintaining a good pressure. It does sound a little like the cam wasn't factored into the tune, but the cam isn't HUGE so IMO it would still run a bit better than your describing.

It sounds like your saying that when you rev it, and then let off, it tries to die and then come back up? Check for vacuum leaks. Does it rev up normally and sound/feel ok? If it bogs or runs wild, check the tps and MAF.

[JJAB]

You are exactly right, it does bog a bit when I try to accelerate. I am about to check fuel pressure and vacuum leaks.

[clinebarger]

Idle Air Control motor (IAC) problem? Pull the vacuum hose off the fuel pressure regulator, If there is fuel in the hose/leaking from the regulator.....The regulator is bad.

The IAC doesnt like to sit for long periods of time. They get sticky or stuck.

[Super73]

This is a great example of why mail order tunes do NOT work. Find a local tuner and bring them the car or, buy HPtuners and learn how to do it yourself. I don't care how good a tuner is, they can't see, hear and feel the car being tuned through the mail box, so really you end up with a tune that is not right (really making them a bad tuner). People on HPtuners web page (myself included) will often look at data logs and tunes that you have trying to help you sort out your problems. When we can see a data logger it helps to give you more options/suggestions.

A cam will also cause a low speed idle and dieing when coming to a stop or even free reving. The thing is though, that cam is pretty small and I would be shocked if even a stock tune would cause the motor to die with the specs you provided. What is the intake centerline and LSA of that cam? If the LSA is rather small, there might be enough overlap to cause the computer to freak out.

If it was an IAC motor it would normally stick, and when it sticks, most the time they stick open causing a higher rpm. The tuner could have set the IAC motor counts to some semi weird setting for the cam.

There could be a lot of things causing the issue. Do you have a MAF on the truck?

[JJAB]

Yes I do have MAF on the truck. Here is a little more information. On initial start up, I have to actually press the gas pedal to crank the truck. Fuel pressure is 58 to 60 on the rail. Again as it is idling, if I accelerate the motor, when it comes off of acceleration it idles rather low like it wants to die and the MAF sucks ev en harder(louder) during this low idle. I also took the vacuum hose off of the regulator and no gas was in the line. The only code that I am pulling is P0650 MIL. The motor actually acts as if it has a dead miss to it. During acceleration, it is not a smooth acceleration, not a responsive acceleration. Lastly, for the heck of it, I pulled each coil wire off while the engine was idling and damnest thing, the motor did not respond it. Not once did the motor act like it wanted to die or miss worse. That was strange. Any suggestions??

[BR3W CITY]

any chance the cam is installed 180* off?

[Super73]

Try these two things, both may throw a code but can be resolved once put back..

Unplug the iddle air control motor (On the throttle body), fire it up and see what it does.

Unplug the MAF, that will put it in speed density mode and rely on the VE table.
--- Do this when it's cold (under 140 degrees) and it will not use the O2 sensors to adjust AFR. See how it runs
--- Also do this when it is warm (past 160 degrees) and it will use the VE and O2's.


Let me know if either of those make a difference.



Unless the cam mfg messed up on the cam, it is not 180 out. They have 3 holes and a pin to make sure the cam gear is set right and the crank has a key for the lower gear.

[JJAB]

Thanks, I will try these two things first thing in the morning. One more thing about the cam is that, a cam grinding company reground my cam. Therefore, the cam was reground on the "back side". Just trying to give all information that may be pertinent!!

[BR3W CITY]

wait, did you buy a hot cam or have a cam ground from your stocker.

[JJAB]

I had a cam ground from my stock cam.

[JJAB]

When I unplugged the IAC (cold, under 140 degrees), I did crank it without pressing the gas and while accelerating it, it did not die or stumble close to dying. Nevertheless, it still has a miss or when accelerating, it is not a smooth acceleration. Now as it warmed up, I plugged the IAC back up and cut the vehocle off. I then unplugged the MAF. When I cranked it back up it barely caught without having to press the gas and then it raced to a high rpm well abve 1500 rpm and just stayed there. The MAF was sucking very hard the whole time.

[JJAB]

Speaking to the company that ground the cam, they said the cam was ground on 116.

[Super73]

So when they ground it, where did the ICL and LSA fall? Are the centers still stock?

[Super73]

If I am reading this right, you:

Only had the IAC unplugged when cold?
Once warmed up, you plugged the IAC back in?
You only unplugged the MAF once warmed up?

Basically when bellow 140* the vehicle is in what is called open loop, and normally does not use the O2 sensors, but still uses the MAF and VE table. If you disconnect the MAF, it relies solely on the VE table until > 140* then it uses the VE + O2 sensors.

Redo the test with the engine cold and MAF disconnected. If you have a video camera, record it because that might give me a little more to go by. If you record it, give me information as you change things. Like "temp is x* and I am unplugging/plugging in MAF"

[usmcchevy]

How long have you let it run? I had a bad tune (W4M) that would need to learn to idle. It took a a few seconds of me not touching the pedal and letting it try to run on its own for it to pick up. After learning it would be fine until you disconnected the battery, then I needed to let it learn again. Sent it back to him twice, same junk. Different tuner got it the first time.

[JJAB]

Well, I have let run for 5 to 10 increments at one time. But, the only time I do not have to touch the accelerator to start it is when I unplug the IAC. To eliminate the possibility, I will be installing new IAC, TPS and an o2 sensor. Thanks for the information and suggestions!!!

[68GMCCustom]

On the miss....have you pulled the plugs to see their condition and that all are firing?

[Super73]

Also as far as the computer learning things out, if the Ltrimms are farther than +/- 25, it will not be able to compensate for it not matter how long you let it run. It is not that hard for a cam to mess things up that bad. The closer to 0 the easier.

A faulty O2 on one bank can cause the computer to freak out as well, one side reads lean while the other reads rich skewing Ltrimms bank to bank. The computer does not compansate bank to bank, just a general fueling based on the average of both banks.

[JJAB]

First of all, Thanks to all that offered their helping advice. I ended up having to get a custom tune. During that tune, I learned gobs of information about my truck/LS motor. During the tune, I learned that the passenger o2 sensor was not functioning properly. I also learned that i had a small exhaust leak on that same side that was actually throwing the os sensor readings off. The tuner really knew his stuff, unfortunately what he ended up doing was turning my 02 sensors off, then tuning it. He has scheduled a return to properly tune it when I fix the exhaust leak.

Different subject, if my 1980 truck did not come with a power brake booster, how difficult will it be to integrate one. Will it help me? The autozone master cylinder that is on it can seem to stop leaking fluid.

[68GMCCustom]

sure.....my truck had manual/drum brakes. Now has power brakes w/front discs

[BR3W CITY]

you can definately add a power booster, but since I see you have a 6.0, check out the power steering pump for me. If you have 3 hoses, you have the option of adding a hydra-boost brake system. This gives you really nice brake pressure, and isn't vacuum dependent. It also doesn't need a big booster diaphragm, which can cause interference with the valve cover coil packs on some swaps.