I have been having misfires on cylinders 2 and 3 on ignition, and it improves within a few minutes. As a result, I recently did a used oil analysis at Catapillar. They found coolant in my oil.

I have a 97 f-150 with 4.2L.

Should I get a compression check done? Or a radiator pressure test?

2ndly, should my work be done at ford or my regular mechanic?

 

Do you have your original intake manifold gaskets?

In case you were not aware, there was a serious problem with the '97 and early '98 V6 motors. Coolant can leak into the cylinders. If a cylinder fills up with water while the truck is at rest, you can do serious damage starting the motor (bent connecting rods, ruined crank).

Later motors used revised gaskets.

If you have your original intake manifold gaskests, I would strongly suspect this is the problem, and I don't think it would show up on a compression check.

If you do a search on this issue, you will get lots of info.

 

The coolant leak in question would be in either number three or six cylinders on the rear wheel drive 4.2. The only way coolant will get into a middle cylindier is a cracked/warped head. You probably have two problems. One, the coolant is in the oil, most likely from faulty intake gaskets, and two, the EGR ports in the intake are clogged causing your misfire. Try unplugging the vacuum hose on the EGR valve then drive it. If your miss is gone, the plenum needs to come off, and clean out all the ports. If your intakes are leaking, you will have the intake off anyway. These are the first things to check on this engine for these concerns.

 

Ya I have the same problem with my Ford its a 1998 4.2 v6 I am loosing coolant and there are no leaks at the hoses or rad.... you think its the head gasket? I dont have any miss firing yet but I notice that there is some white film on the oil cap on the inside. Is it hard to replace the head gasket on those models?

 

Thank you. I had a hard time believing that the coolant was causing the 2 and 3 to misfire.

The misfires only occur on completely cold starts (ie. 8 hour+ shutdown). Any explanations as to why clogged ports would be most sensitive then?

 

Dan, if #2 and #3 are misfiring and there's coolant in the oil, you probably have a blown head gasket or a cracked head. You need to do a compression test. Nikoli, you probably have leaky intake manifold and/or front cover gaskets. Both of you are looking at a possible hydrolock at any time.

 

First off, I have yet to see a blown gasket on these model trucks. The gasket is a multi layered steel design. Only severely neglected coolant causes problems with them. The reason the egr causes the miss is that the other ports clog up and dump all the egr into the unrestricted passages. Egr gasses are spent combustion and do not "fire" when entering the combustion chamber. The egr will open up under slight acceleration. That's why I said to unplug the vacuum and see if it goes away. Number one reason for coolant in the oil is the intake gaskets.

 

Thank you. Pressure tests did not work, but when they removed the gaskets, cylinder 2 gasket was broken.

They also cleaned out the egr.

Problem fixed.

 

The miss fire goes away after a few mins of warming up. ... I just ran into the exact same thing on my OLDS Alero. What is after hours and hours with lab scope and checking every thing else. ( injectors, plugs, wires, coils) ext. it came down to a leak in the plastic lower intake gasket. This allows a tiny bit of air past when cold leaning out the cylinder. It only happens ant 10 to 45 degrees bellow that its cold enough that the engine fuels like mad for a cold start warmer it doesn't do it cause the gaps close.

On the other side if you do suspect that it is coolant related, its fairly easy to detect. Pull the plugs (its probably a good time to change them anyway) coolant has a tendency to super clean the ceramic on the plug. If coolant is getting in the plugs will be gleaming white rather than the more golden colour the other plugs should be.

Cheers and good luck