L29 starting issues. Any ideas?

[shady]

The l29 burb I recently bought seems to run good when running.
But,,,. When starting it it'll crank and crank and crank AND crank..... Almost stumbling to life occasionally. And even being FI if I pump it a little while cranking it will catch and run.
Then runs pretty decent afterwards.
Seems to start batter after it's ran a bit and you don't leave it off long.


My thoughts are,. Fuel pressure bleeding off, the relay that bumps the pump when the key is first turned on is bad, or I've heard of ignition module issues with them but figured it wouldn't run at all if it was that.

No, I haven't really done anything to troubleshoot yet. Just getting some possible ideas where to start lol.

 

[Capt Ron]

I had similar issues with my L29.
Replaced the injector wiring harness and it starts/runs much better.

 

[swettysblazer]

Do these have the spider injector like the other Vortec motors? Could be that as well, I know on the 5.7 that was common and the new spider would fix it.

 

[ZooMad75]

Do these have the spider injector like the other Vortec motors? Could be that as well, I know on the 5.7 that was common and the new spider would fix it.

No spider bs on a L29. But due to the 2 part plenum design they have 1 fuel rail that feeds both banks of injectors. Runs down the center of the lower intake.

The stumble to life hard starting is most likely fuel pressure bleeding off after it sits for a few hours or more. There is not separate relay to prime the fuel system. It’s just the only fuel pump relay being commanded on for 3 sec when the key is turned to the run position.

If the fuel has bled off over time the 3 second prime is not going to push enough fuel up to the injectors and build pressure for the injectors to work. There is a small amount of pressure that can stay in the line if there is no leak, but more importantly it’s having fuel already up to the engine in the line to allow the 3 sec prime to build pressure for the injectors.

Try cycling the key from off to run wait 3 sec, shut the key off and repeat 2-4 times before attempting to start. If it starts better you are on the right path. Time to look for the leak.

Leaks can be not leaking fuel on the ground. There’s a check valve in the pump that helps hold fuel in the line with the pump off. If that fails it would give the hard start after sitting. The other source is an injector or multiple that are stuck open that allows the pressure to bleed off.

A fuel pressure gauge is very helpful here. Turning the key on with the gauge installed should have the gauge jump up to 40-50 psi right away. If it don’t, cycle the key again and see if it goes a little higher. I’d start the truck and monitor the pressure as it should be 55psi. Shut the engine off and watch how fast the pressure drops. Even when everything is ok you will see pressure drop but it will be really slow. You are looking for a fast loss of pressure.

If you do have a fast drop you can isolate the check valve or injectors by pinching off the return line with a soft jaw clamp. Build pressure and clamp off the return and then watch the gauge. If it continues to drop fast it’s on the injectors if it stops it’s in the check valve at the pump.

 

[82355]

My old man’s ‘98 K2500 was the same way for years. I always need ruined fixing it for him, he didn’t want to.

Martin

 

[shady]

Fuel pressure was one I was going to check first. That and sticking the scanner on it.
The engines coming out and getting some love to go in my dually anyway. But figured I'd try and figure it out now before I swap.

Gotta get the hood open first though lol
It opened real hard when I got it, I drove it to the shop, unhooked the battery due to something under the dash clicking continually with the key off, and shut the hood again like a dumbazz

 

[Truckman4life]

I have a Mazda truck that had a weird hard start when got it. Someone had rewired the fuel pump circuit to an ignition feed to bypass a shorted factory circuit. The pump would come on with the key then off while cranking then back on when you stopped cranking. So if you didn't get it to fire off the initial pump run then hurry and stop cranking for the pump to come back on then it wouldn't go.

 

[dyeager535]

This almost sounds like previous years that used an oil pressure switch when the fuel pump relay fails. IIRC GM was using the same design relays on the firewall for AC and fuel pump, so swapping the connectors between the two relays before trying to start a cold engine would be an easy test.

I did see the results of a split in-tank fuel hose (thanks ethanol) with a fuel pressure gauge, as pressure bled off immediately after the pump shut down.

 

[Wes Harden]

To me it sounds like the iac is stuck closed, the engine doesn't get enough air. When @shady pedals it it gets air and starts.
Computer then compensates for reduced iac air.

 

[shady]

I'm not sure if this is it or what..... But I took the battery out and slow charged it for a couple days. Stuck it back in and it started up immediately.
The odd clicking under the dash when I shut it off didn't happen either.
She had said she had to jump it to get it home, and jumped it every time she started it after that, and every time it barely started.
I'm wondering if it just didn't have enough voltage or something to make the system happy while cranking .
I'm going to hit the key again this morning just to see what happens.

Doesn't seem like that would be it. But it was definitely the first time I've seen it start that quick. I've helped her jump it 5-6 times myself before I bought it.
Every time I've helped it was with semi truck size cables and the biggest optima yellow top they sold when I bought mine.
(I know yellows aren't really a starting battery lol)
I didn't even give it time to prime. I just wanted to see what the battery was going to do.