1996 Chevy K3500 454 rough running problems

Landmanil

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Nov 15, 2005, 3:36:14 PM11/15/05

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I've had my 96 K3500 with a 454 7.4L engine for a few months and ever
since the weather cooled down from the hot summer days it's hit or miss
everytime I try to start it.

Now when I try to start it, it starts up running very rough about 70%
of the time. It usually stays running like this for 15-20 min and
mysteriously it runs normally again. When it's running rough, the rpms
head down from the 1500 or so to about 600 and bounce back up to 1500
back and forth until it heats up. It runs fine otherwise and it's been
relatively well maintained.

I've been throwing parts and work at it for a while hoping to catch the
problem but so far no luck. It has a full tuneup done with plugs,
wires, cap & rotor, changed Idle Valve, changed upper and lower intake
manifold gaskets, and changed EGR valve. My next guess is that it
might be fuel related, maybe an injector, fuel pressure regulator, or
fuel pump relay??

Please help, I've been scratching my head about this problem for a
while and I need to fix it before winter hits.

Thank you

Daveman

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Dec 7, 2005, 12:01:33 PM12/7/05

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You may want to check the crank sensor and the distributor sensor. I've
got the same motor in a 3/4 ton. Had that problem. Computer couldn't
figure out where it was firing. Mine was deeper though. Gear on the
bottom of the distributor was installed wrong during the rebuild. Threw
the computer completely out of wack!

harold

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Feb 26, 2013, 1:18:01 AM2/26/13

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replying to Landmanil, harold wrote:

> I've had my 96 K3500 with a 454 7.4L engine for a few months and ever
> since the weather cooled down from the hot summer days it's hit or miss
> everytime I try to start it.
>
> Now when I try to start it, it starts up running very rough about 70%
> of the time. It usually stays running like this for 15-20 min and
> mysteriously it runs normally again. When it's running rough, the rpms
> head down from the 1500 or so to about 600 and bounce back up to 1500
> back and forth until it heats up. It runs fine otherwise and it's been
> relatively well maintained.
>

you might have a coolant sensor problem that is for the computer in the
summer time its warm but in the winter it is to cold so I would go with the
coolant sensor for the computer

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madashell

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Dec 11, 2015, 10:18:01 AM12/11/15

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replying to Landmanil, madashell wrote:
I have 96 Chevy 454 had a small miss. Been in the shop on & off for2 months.
They ccan'tffind the problem. Its worse now runs ruff all the time now.
Replaced crank sensor, MAP sensor, distributor, rotor, cap, wires, plugs, fuel
pump, sock, filter. Coil, module. Please help. lucky...@gmail.com

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cl...@snyder.on.ca

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Dec 11, 2015, 1:40:46 PM12/11/15

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On Fri, 11 Dec 2015 15:18:00 +0000, madashell
<065b0505594b06f549...@example.com> wrote:

>replying to Landmanil, madashell wrote:
>I have 96 Chevy 454 had a small miss. Been in the shop on & off for2 months.
>They ccan'tffind the problem. Its worse now runs ruff all the time now.
>Replaced crank sensor, MAP sensor, distributor, rotor, cap, wires, plugs, fuel
>pump, sock, filter. Coil, module. Please help. lucky...@gmail.com

Have the mechanic check your valve lift - all 16 of them. My guess is
you have at least one flat cam lobe.