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98 k-1500 hesitation off idle

Cornfield creations

Cornfield creations

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Oct 19, 2005
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Jasper, Indiana
I recently got a 98 k-1500 w/ 5.7 w/ 181,000 miles for a daily driver. Bought it with a miss in the engine. No prob right?

I replaced the cap and rotor, plugs and wires. No go. Then I did an intake and fuel system cleaning, which I got to run the gas out of it before the cleaner in the gas will do its job.

Today I replaced the distributor gear, I know they have problems, and sure enough the gears were worn.
So I set the distributor and got the cam retard set at 0*.

Sure enough it took care of the miss it was having.

But now it has a a hesitation off idle, most of the time. Driving it down the highway it seems to get better. Whenever it at least hits 1000 rpms it doesn't do it, but at WOT it will hesitate and then take off.


I was thinking it may be dirty or bad injectors, or maybe play in the timing chain. What do you guys think?:confused:
 
Check your coil sounds like weak spark perhaps. Spray wires down with a spritzer bottle and perhaps you can find a bad plug wire?

I'd run through the basics first. Check vacuum, check spark, check timing (ya did that). Then report back.

O and dont scoff at the spritzer bottle trick it works very well at finding a spuratic bad wire. Nothing should happen when you spray them. If it stumbles you got a bad wire.
 
had a 96 vortec 350 did the miss / hesitation when cold. clean the mass air flow sensor.

and if you didnt use factory acdelco plugs you will get funny idel/ run problems under load.
 
I replaced the cap/rotor/wires/plugs with ac delco parts. I just tried cleaning the MAF and it didn't change although it was dirty as usual. I am thinking a dirty injector. I may run this gas through it and see if it changes. Thanks for the ideas, I doubt its the timing chain since I just started it since yesterday and it is worse than it was last night. After warming up some it gets better.

The PO obviously was trying to figure it out. He replaced the plugs, O2 sensors, fuel filter and some other things.

Also this truck isn't a z-71, but I thought all these trucks had the oil cooler to the radiator. This one doesn't, but that shouldn't shorten the life of the engine too much if at all right?
 
Cornfield creations said:
I replaced the cap/rotor/wires/plugs with ac delco parts. I just tried cleaning the MAF and it didn't change although it was dirty as usual. I am thinking a dirty injector. I may run this gas through it and see if it changes. Thanks for the ideas, I doubt its the timing chain since I just started it since yesterday and it is worse than it was last night. After warming up some it gets better.

The PO obviously was trying to figure it out. He replaced the plugs, O2 sensors, fuel filter and some other things.

Also this truck isn't a z-71, but I thought all these trucks had the oil cooler to the radiator. This one doesn't, but that shouldn't shorten the life of the engine too much if at all right?
Click to expand...

Oil cool = not necessary in a stock or mild application.
 
sounds like an old fuel filter of a pump going out, if it's never been replaced, with 181k miles, it's about due.
 
that would be my guess then, more than likely that was an idle pressure reading as well, when you get on the throttle, it's gonna drop down even more more than likely, essentially starving the motor until pressure catches up (somewhat)
 
K next step is to disconnect each injector one by one. If your fuel pressure doesnt go up on one of them you have an injector stuck open.
 
i had an injector stuck open once, it flooded the throttle body area where the injector sprays. I doubt it's a stuck injector, still sounds like a low fuel pressure to me, yeah it would go up to 60 when you rev it, but it's suppose to be there at idle, and go up even more when you get on the throttle.
 
4xcrazy said:
i had an injector stuck open once, it flooded the throttle body area where the injector sprays. I doubt it's a stuck injector, still sounds like a low fuel pressure to me, yeah it would go up to 60 when you rev it, but it's suppose to be there at idle, and go up even more when you get on the throttle.
Click to expand...


Its is vortec theres alot of intake to fill.

Also remember it doesnt have to be stuck 100% open.
 
Well when I turn the key off it maintains pressure. It doesn't leak down.

I keep thinking a dirty injector is probable, it is also intermittant. When the engine is warm it does it less, and sometimes it doesn't do it.
 
OK this is awesome. So I drive it home last night, runs actually pretty decent, then I start it up this morning and it starts missing REALLY bad. Cylinder 3 and mainly cylinder 4. Same as before, but after it warmed up it ran like it did last night, just barely hesitating off idle and during slight acceleration.


I am probably gonna try and pull the upper intake off and see if maybe an injector is bad or what is going on in there.

Here is another question. I have been seeing kits for converting from CSFI to MFI. What are the benefits for this kit? I don't want to spend $400 and find out it was useless.
 
the orignal spider injector setup sucked. love to plug up injectors.

upgraded style thay sell now works a lot better.

as far as i know both are non servicable.
 
IC, I did some research and yeah, something they should have done from the factory.

I talked to my goto guy at the dealership. He said that they have problems with upper intake manifold vacuum leaks. He said the way I described it it sounded like that is the issue, since when its cold it horrid, then when it warms up it gets a lot better. I tried spraying carb cleaner around the upper like he said but the engine was running so erratic that I couldn't get a baseline. I was planning on take the upper plenum off and checking it out anyways, so it will be a good time to change all the gaskets and clean the poppets.

I'll update after I get her finished for those with similar problems.
 
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