The shop that is looking at my jimmy made the conclusion that it could be my intake manifold gasket... Would this cause a random misfire?

 

Although intake gaskets can leak vacuum and cause a misfire, they're more likely to leak coolant, internally and/or externally. P0300 through P0306 DTC's are almost always caused by secondary ignition faults; ie spark plugs, spark plug wires, distributor cap, rotor, shaft bushings, and ignition coil. Low fuel pressure can also cause them to set but it usually sets other DTC's along with them.

If they are leaking vacuum, it seems odd that it's causing random misfires rather than continuous misfires on a given cylinder. "Random" implies not the same each time, which would mean the vacuum leak only happens at times.... odd, but not impossible I suppose.

 

Also: There is no crank position relearn for a 96 so you can rule that out.

 

They drove it around again yesterday and it wasnt the same cylinders this time. But they want to charge me an arm and a leg for the job. Im going to do it myself. Is there any pointers you can give me? or anything i should watch out for?

 

Have you tried propane enrichment where the intake manifold meets the cylinder heads? An increase in RPM or oxygen sensor voltage would indicate a vacuum leak. Fuel trim should also provide information confirming a lean condition if there's a vacuum leak. Are there any internal or external coolant leaks? If you can't confirm a problem with any of these, you're probably wasting time and money replacing the intake gaskets, in hopes of repairing the misfire.

What were the readings for fuel pressure and leakdown rate? Have you checked camshaft retard?

 

They did see an external leak of coolant on the manifold. and its a little damp after driving around the intake manifold itself. They did not tell me what the leakdown was and camshaft retard meaning the distributor is off a tooth?

 

If you don't have a propane bottle you can use carb cleaner or starter fluid to test for a leak. Just spray it around the manifold while the truck is idling and if there's any change in rpms you have a leak. However since you have coolant oozing from the intake I'm guessing you already know that your gasket is bad...

 

If the distributor is off one or more teeth, P1345 will set and the SES light will come on. Camshaft retard has to do with synchronizing the CMP sensor with the camshaft so it sends correct data to the PCM. Installing the distributor with proper mesh, (no P1345) is a "rough" adjustment. The "fine" adjustment is made by rotating the distributor. The PCM uses data from the crankshaft and camshaft position sensors for several things, among them is identifying which cylinder is misfiring, and when to fire the ignition module.

Just because the intake is leaking coolant, doesn't necessarily mean it's leaking vacuum. Don't misunderstand, if it leaks either one, it needs to be replaced. But keep in mind that if it's only leaking coolant, it will not cause a misfire.

 

Doesn't that sound like a solonoid issue? The shudder does make me wonder if its a loose TC as well though. Ignition products from reputable sources should not cause any of the issues you describe-I have never experienced the so called AC preference in ANY 4.3 I have owned! How is the trans mount/u-joints? Just wondering...

 

Similar symptom, but he's getting a P0300, random misfire.