Need some engine diagnostic help:

[Graystroke]

1996 Suburban 3/4 ton w/ Vortec 454. Note:The 454's have Sequential EFI and not the central pod thingy on the Vortec 350's.

The symptoms: Every now and then when I try to crank the engine it doesn't want to fire. I have to give it throttle to get it to catch...which is no bueno in an EFI motor.
Also, when it does this as you start to drive it and you floor it it pings bad under load (not all the time). Has a miss a idle too. Not a steady one just every so often. My first guess is either ignition or fuel pump. Truck has 78,000 miles. All the wires, plugs, cap, and rotor have been replaced....so I'm thinking fuel? Maybe the pump is on its last leg? check valve is failing and the system has to reprime up to the engine?
The other thing I think is wrong is when it starts up it seems to really throttle up high at first. It revs to about 1800 RPM then settles down to a high idle (which I'm guessing is normal for when it's cold outside) of around a 1000 RPM until it warms up just a tad, w/in a few minutes-then drops to 750 RPM. I replaced the IAC, thinking this was the problem w/ the idle at start up and it didn't help any.
No check engine light....I'm figuring since there is no Check engine light that there wouldn't be any codes stored. Chevy fuel injection is a new one on me to what are typical problems. The Haynes manual sucks balls b/c they cover absolutely nothing when it comes to Vortec 454's...not even a pic in the book. The book pretty much reads: This is how you remove/fix problem "X" on a Vortec 350...If you have a Vortec 454 it's different and you're **** out of luck.

[agjohn02]

fuel filter? try it, then think complex stuff.

[Graystroke]

already did

[agjohn02]

timing? at 78,000 it shouldnt be the pump. make that your last resort since its the biggest pain to fiddle with. i dont think the high idle is a symptom, just a side effect of cold. my vortec 350 has 180,000 on it and i havent had to mess with it other than tune ups so im not familiar with specific problems.

[aggieblazer07]

to check the fuel pump you can use a pressure gauge, I'm not sure how much it needs I think it's around 26? but that way you don't have to take it off and check

[mudtoy67]

Sounds like the computer might be getting a bad signal somewhere. I've run into bad temp senders sending the wrong temp to the computer and throwing timing/fan control/ idle/ etc... out of wack. Even though you don't have a check engine light on I would hook it up to a scanner and just look at the values the different sensors are giving while the engine is running. You might find something that is wrong enough to throw things off but not wrong enough to throw a code.


I think fuel pressure on the port injected motors is 40-60 psi. Have you had your injectors cleaned with that pressure cleaner that goes directly into the fuel rail?

[uglyota]

what plugs did you put in it?
John a vortec 350 is timed by the comp, I imagine it's the same for a 454

[agjohn02]

John a vortec 350 is timed by the comp, I imagine it's the same for a 454

its got a dizzy doesnt it? if it gets twisted, the comp can't compensate with enough retard or advance.

[uglyota]

yeah but it's fixed. If it's twisted it's broke

[Graystroke]

yes it has a dizzy but it also has a cam sensor. you stab it in and just get it close and the computer is suppose to take care of the rest as long as the spark isn't jumping terminals on the cap. I thought it was weird to when it said do not adjust the timing and there was sitting a distributor. I'll try the scan and see what happens. It also cuts out sometimes at full throttle when reaching RPMS in the neighborhood of 4 grand.

[agjohn02]

that cam sensor is what id look at next as long as the dizzy is close to where its supposed to be. i dont know how the advance is controlled, but it prolly got some sort of comp controlled vacuum actuater or solenoid. might look for vacuum leaks or a bad actuater.

[BMFScout]

wtf's a dizzy?

[uglyota]

a british distributor...they run on petrols

[Graystroke]

i dont know how the advance is controlled, but it prolly got some sort of comp controlled vacuum actuater or solenoid. might look for vacuum leaks or a bad actuater.

It's all computer controlled. all there is is a plug on the side. The cap is one of those funky ones where the wires all come out in order on the side. one side is 2, 4, 6, 8 and a place for the coil and the other 1, 3, 5, 7.
I don't think there is a vacuum leak, what I initially thought. I've sparayed a whole can of Beriman's (sp) carb cleaner all over every vacuum port and all along the manifold.
Where can you get this "pressurized" FI cleaner. It plugs in the fuel rail pressure reading port, right?
Does it work?
I think I'll take a reading on the rail and see what pressure I got.

[robertf03]

is your tps adjustable?

how much throttle do you have to give it? do you just hold it open a little or do you have to hit it like your pumping a carb?