Mechanics on here?

[catmandoo]

My 98 GMC 350 vortec is missing while cold, not sure if it is spark or fuel but it misses until full warmup then its ok again...any ideas on what it may be? The truck has 250000km on it and the plugs and wires had to be replaced at 125000 because of a real bad miss, this miss now does not seem as severe as the one before with the plug wire issue.
Thanks

 

[Cowbell]

Check your vacuum lines. Just an idea. If it was a spark problem I think you would have it all the time.

 

[SLEDIOT]

Put some fuel deicer (isopropyl) I think, in yer tank you probably got some water in there.......

 

[stum1967]

Is the coolant level staying full? Those engines had a lot of intake manifold leaks. Sometimes you get a little coolant leaking into an intake port and it will miss on cold start. My 98 gmc 2500 did that around 100,000 miles.

 

[wildcard28]

Stum1967 was thinking what I was thinking those are known for intake gasket leaking and sucking air from inside of outside the engine causing a miss in one or more cylinders,

Also should find out if the miss is erratic of definetely a certain cylinder. If it is a certain cylinder missing and only that cylinder I`d run a compression test on that cylinder and if compression under Id say 90 to 100 lbs or less Id check the others to define whether you have one or more cylinders weak. I put a new engine in a truck a few weeks ago and had a constant miss and found out that one of the sparkplugs I put in must of been dropped and it closed the gap in the plug it missed but not all that bad . the cylinder was firing but that plug was obviosly different than the others.


Good Luck.

 

[89sandman]

the intakes gaskets on those are made of plastic and the water crossover ports have a rubber gasket molded into the plastic, when the plastic misforms and breaks this allows the rubber seal to move and causes it to leak. am doing one in a 99 van right now at the shop. if your not using any water the next thing i would do is scan the computer, almost always with the intake gasket going bad the water will either leak to the outside or inside the motor, but have seen several with the water leaking into the intake port next to the crossover. the obd 2 computer system has hard codes and pending codes for each cylinder misfire or random multiple misfires. if you think you have a vaccum leak check the live screen data and check the map values. these should be steady at an idle, if you have a vaccum leak the values will almost always be erratic. just a place to start...

 

[catmandoo]

Is the coolant level staying full? Those engines had a lot of intake manifold leaks. Sometimes you get a little coolant leaking into an intake port and it will miss on cold start. My 98 gmc 2500 did that around 100,000 miles.

Yes that was a problem I corrected in the summer,i was allways loosing coolent, so i put in new gaskets and stoped my internal leak, since then the truck ran great up untill a few days ago...and it is now dipping below freezing so SEDDIOT may be right and added some gase line antifreeze and injector cleaner..it ran better today but will wait for morning to see how it acts when cold.
Thanks so much everyone.

 

[JohnnyH]

The first thing that I would look at would be to check for sticking injectors.
Vary common with that motor.

 

[Dippy]

just had the same problem with my 97 chev it ended up being an injecter and a intake manifold gasket, runs like a champ now

 

[1 bad nytro]

Stum1967 was thinking what I was thinking those are known for intake gasket leaking and sucking air from inside of outside the engine causing a miss in one or more cylinders,

Also should find out if the miss is erratic of definetely a certain cylinder. If it is a certain cylinder missing and only that cylinder I`d run a compression test on that cylinder and if compression under Id say 90 to 100 lbs or less Id check the others to define whether you have one or more cylinders weak. I put a new engine in a truck a few weeks ago and had a constant miss and found out that one of the sparkplugs I put in must of been dropped and it closed the gap in the plug it missed but not all that bad . the cylinder was firing but that plug was obviosly different than the others.


Good Luck.

sounds like a leaky gasket!

 

[REV4ARUSH]

I vote for injector also. It would help us all out if you could scan it for codes.

 

[hilinerider]

poor compression, when engine warms up, cylinder fires

 

[Ex-Member]

It would help us all out if you could scan it for codes.

My thoughts exactly. Most auto parts stores have a scanner they'll let you borrow to see what's going on.

 

[catmandoo]

ok gents see what i can do and thanks for your help and understanding.

 

[Blk88GT]

Why not spend the 20 dollars on plugs? You have over 125km on a set! LOL

While you're at it, test the spark plug wires with your volt meter.

 

[Sidehiller]

Don't be so cheap! Go buy a new truck - it's guys like you who try to keep driving old vehicles that are to blame for the auto makers needing a bail out! I'm kidding but I actually heard that line on the news this morning.

 

[catmandoo]

I would and now they are getting cheap to buy but I just don't use a truck that much anymore but will again once the snow falls..as my caddy don't look like it will do well in the snow and ice.

 

[JohnnyH]

If you do end up needing injectors make sure to get the new updated injector assembly.

GM Part numbers

93441235
V-8 MFI Assembly

17113206
V-8 Seal Kit

93442096
V-8 Bracket