6.0 Falls Dead, Cranks Up?????????

[JJAB]

Ok fellows, you have helped me throughout this swap. I have completed the swap and the tuner has come and completed the in person custom tune. It has since been two weeks since the tune. Four days ago, the blazer would crank and run for thirty seconds or so and die out; would only stay running with your foot on the gas pedal. Long story short, I had to re-vent the gas tank. Prior to reventing the gas tank, I had vented the tank by the vent tube or hose that goes to the charcoal canister. I guess it wasn't sufficient. Nowm while driving the blazer, when I come to a stop, sudden or not, the blazer falls dead, but will crank right back up. Thing is, this was not a problem when the tuner was in the vehicle. Help me out if you can.

Here's a little more information:

Single gas tank with EP381 fuel pump, ECM is pulling no codes, fuel pressure regulator is new,truck intake, all sensors are new.

I am running a very short, straight air elbow with a rather cheap, short a filter. I just haven't upgraded it. Couold this be my problem?

[Clyde65]

stock or aftermarket tank?

sounds to me that when you stop suddenly, your motor runs out of fuel....

[JJAB]

It is a stock blazer/suburban tank with the efi sending unit with an EP381 fuel pump.

[BR3W CITY]

Only stays running under heavy throttle and dies on a stop?
The only running wide open part suggests either a vacuum leak, or a problem with the MAF.

Dying on a stop can be a few things; if you don't have tank baffles and were low on gas, then the engine might have just starved. A full tank will reduce the problem, but getting some tank foam or baffles should stop it.

Vacuum leak is still plausible, as the brakes require a deal of vacuum, and with a big lopey cam, its not unheard of to stall out of die under heavy braking (hence the use of hydroboost or vac cannistor).

Last option could be the lockup if your running an auto; I was just dealing with some problems regarding lockup and big cammed auto's; the solution involved the misfire count from the cam, causing erratic lock and unlock.. Staying locked up on decel can "bog" the engine and stall it out for a second. Sometimes its not even a "full" stall, it will drop to 1rpm, not throw lights and then pop all the way back up to 790 at idle.

[JJAB]

I really appreciate the insight. The tank we have does have a factory baffle. I have probably went through a entire can of carb spray searching for leaks. I have started making this a part of the install. So, no leaks. Actually, it runs just as smooth as a baby's bottom idling, even after it may cut out or die after stopping, when you crank it back up, it runs just smooth. Other than that I will explore(evaluate) the other things you mentioned.

[JJAB]

Let me mention another thing. The sending unit has four "outlets", so to speak. I have them connected to the following:

1. Large outlet - Fuel feed to the intake
2. Medium outlet - Designed to go to fuel filler neck - open as a vent
3. Next to smallest - Fuel return line to intake
4. Smallest - connected to hard line that goes to charcoal canister up front,
but it is currently not connected to a canister

I don't know why but I just thought this may have something to do with my problem. What do you think.

[BR3W CITY]

I was confused because in the first post you said it would only run with your foot wide open, but now you say it runs and idles fine...

So it STARTS fine, IDLES fine, and ACCELS fine, but only under ANY sort of braking, it starts to die...then you can start it right back up just fine, repeat?



I don't think the small line would matter, I'd just cap it if you have the other one vented.

[JJAB]

Sorry for the confusion. Yes, keeping my foot on the accelerator was the only way to keep it running prior to me venting the tank via the filler neck vent hose. Now, since venting it(tank), it starts and idles fine. Now, upon sudden or quick braking, the engine dies, but re-starts just fine. Ocassionally, upon normal braking, the motor will die too.

[JJAB]

After driving the blazer again and trying to get very specific sysmtoms, this is what it ooing exactly. First, PCM is throwing no codes. Under normal driving conditions in the city, normal stop and go, the blazer(engine) does wonderful no issues. If you get into the throttle or goose the motor from "light to light", when braking or coming to a stop, the engine dies and really you dont really know its dead until the steering wheel freezes up; cranks right back up. Or, if you get onto the highway and decelerate from highway speeds& rpm's, the engine does the same thing, but will crank right back up.

I am going to cap off the vent tube that goes to the vacuum canister. I am also going to re-attach the larger fuel filler neck vent hose and purchase a vented gas cap to see if this solves my problem.

To those who are using blazer/suburban gas tanks, I am curious as to how you vented your tank. Any information would be helpful. All other things considered, the 6.0/4l60e combo is awesome and runs great. But as you know the little things can sometimes drive a person crazy. THANKS!!!!!!

[BR3W CITY]

Originally Posted by JJAB

if you get onto the highway and decelerate from highway speeds& rpm's, the engine does the same thing, but will crank right back up.

Mine used to go exactly this, you had to *blip the throttle getting off the freeway to stop it from dying. It was staying locked up too long, and bogging the engine....blipping the throttle released lockup and let it coast down. After the misfire count was adjusted by my tuner, it doesn't do it anymore.

[JJAB]

Thanks, last question before you had your tuner adjust that lock up issue, was your computer throwing a code. This blazer is throwing no code. Thanks for the info.

[Jonboy]

Do the brakes make it stall while sitting still? If they do, you may look into a faulty brake booster. If that is not the issue, is it possible your brake switch is hooked backwards and causing the TCC to lock with the brakes applied rather than making it unlock? If it occurs only while driving, sounds like a TCC fault to me.

[JJAB]

Thing is, i dont even have the brake switch hooked/wired to the tcc. Could this be my problem?

[BR3W CITY]

No codes were being thrown, we had it hooked up to HPT watching the misfire count and watched to see when it commanded lockup. We just put 2+2 together, then found out that it was a problem a bunch of people had but didn't know how to fix.

You NEED to connect that brake switch to the TCC, get a 4 post brake switch if you don't have one currently.

[JJAB]

Okay, you say hook it up to the TCC, where is that connection going to. Will that wire be coming out of the pcm? Do you have a schematic to show me where to hook up to the tcc?

[BR3W CITY]

I have an aftermarket harness, and a new body harness that uses NONE of the stock colors....might prove trickey for what your doing.

IIRC there should be 4 wires, mine were pink, purple, green and white, but yours won't be.



and here's what I used.

[JJAB]

THANK YOU!!!!!!!!!!!

[clinebarger]

Originally Posted by BR3W CITY

I spelled Ignition wrong

[BR3W CITY]

hahaha, was it you i stole that from? Credit for the spelling error is all yours

[clinebarger]

Originally Posted by BR3W CITY

hahaha, was it you i stole that from? Credit for the spelling error is all yours

[JJAB]

Gentleman, no solution as of yet. Lets be more exact of the symptoms. First of all, on initial crank up, motor cold, truck cranks fine. As the truck/motor warm to operating temperature, the motor will begin to stumble/bog down and shut off. Now at this point, the truck is in park. I also have a fuel pressure guage attached and while idling, the guage is reading constant 50-52psi. When the key is turned to the on position, the guage reads 60 and then after crank it settles at 50-52psi. That being said, this is not a fuel pressure issue. After re-cranking the truck about ten different times, the truck began to idle and run longer and better. As I drove the truck this is what it would do. Normal driving, 20 to 30 mph, drives fine or balls to the wall, it responds, but either scenario, when I ease or come off of the accelerator, the motor bogs and and goes dead. But everytime, it will crank right back up. Also, battery tested 13.5 to 14 volts before and during the test. Any help is appreciated.

[Clyde65]

Bad relay? getting hot, maybe to the injectors or?

[BR3W CITY]

50-52 still seems low as on-rail pressure should be around 58... 50 should get it to run but it still seems a tad low. That pump should be able to maintain 80-90 psi (unregulated, according to the manufacturer).

I'd think about the possibility that your internal regulator is not working properly, or maybe your fuel pump isn't wired properly and overheating, or over-drawing on the wires. Is your fuel pump hotwired, wired off a relay, direct, which?

[JJAB]

It is wired off of a relay. This truck has a custom harness made from Nelson in San Antonio. We are just totally mind boggled because we beat this 6.0/truck nearly to death during the tune and it didn't exhibit any of these problems. I guess stuffhappens, huh?

[JJAB]

Not sure if I mentioned it before, but the pump os an Airtex 3270. It is supposed to be the equivalent to the AC Delco EP381just a different brand. Specs say there two different EP3270 pumps with the same part number, one supplying 65psi and the other supplying 80 to 90 psi. Either way this pump should be sufficient, right? What would cause the pressure to be backed down to 50 at idle. The regulator is new but maybe I need change anyway.