Missing when cold

[spdy0001]

For about a week now when I start my 91 it will miss and jerk going down the road until its warmed up. Even when its warmed up its not 100%. I put dry gas in the tank as a remedy, however im not too hopeful. The plugs and wires have about 15-20K miles on them. I have recently lost about a 1/4 gallon of coolant but I can't guarantee yet that I don't have a leak. Just changed the oil and it doesn't look milky and there appears to be no coolant in the tail pipe. This weekend I think I gonna pull the plugs and replace them to see if it helps. Its weird though because it will barely run now when its cold but as it warms up after a few miles of driving it seems to get better. Almost as if something has sealed up or its burnt the fluid out of the cylinder.

 

[manaen]

when is the last time you gave her a tune up? (plugs wires etc..)

 

[spdy0001]

See my original post.

Thanks

 

[manaen]

Hah Sorry, missed that somehow

I would run a fuel pressure test on it, also have you ever changed the fuel filter. It could be low fuel pressure caused by a bad FPR or clogged filter which will casue a lean condition. Is your CEL light on?

Also it could be a vacuum leak which will look much like the low fuel pressure problem.

When you take out your plugs look at how they are burning, also running a vacuum test will reveal engine condition and exhaust condition

This link has a good explaination of running vacuum test
http://www.v8sho.com/SHO/IntakeManifoldVacuumTest.htm

 

[manaen]

Here is a plug condition chart to use to compare the conditions of your plugs
http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

 

[Bwana Bob]

How about cleaning the Idle Air Control (IAC) servo?

Bob

 

[manaen]

that will only cause idle problem, maybe I misunderstood your post but I assumed it occured throughout the rpm range. not just at idle

 

[grufman]

Coolant loss means the coolant is going somewhere. If it's not leaking from a hose or a radiator, it's sucked into the engine. This is why it runs rough when it's cold (the heat expands the cylinder head and seals the leak). This is also why it does not run perfect even though it's warm = loss of compression.

Check your radiator hoses. They should be stiff, but not super stiff. There should be no exhaust smell in the radiator.

My $0.05 = cracked cylinder heads (they crack between the valves)

 

[spdy0001]

Thanks for the ideas guys, but I replaced the plugs and wires today and she now runs perfect again

I also think I found the issue. The first plug I took out was cracked at the point where the spark happens. Looking this up online shows its mainly caused by detonation, which my truck does alot at full throttle. Maybe ill bit the bullet and start putting plus gas in it instead of regular.

 

[manaen]

detonation in these engines is commonly caused by carbon buildup. There should be no reason to run anything but regular gas. Unless of course you start to modify things a bit.

I would run a seafoam treatment on the engine to clean up the carbon, and see if that helps your detonation.

 

[2doorsplor]

top off the tranny fluid. that happend to me when it was cold, and i noticed my fluid was low. solved the problem