Multiple misfire with a warm engine while accelerating.

[JayT]

Vehicle is 97 Aerostar, 3.0V6, 212,000 miles. Multiple misfire is the only code I am pulling right now. Symptoms are as follows:

1. Starts up quick cold or hot. Idles fairly smooth.
2. City driving on cold engine better than when warmed up.
3. Notable misfire on highway at cruise and light acceleration, and more pronounced on warmed up engine.
4. Misfire dissappears on heavy acceleration.
5. Fuel econony drop of 3mpg.

Repairs done so far:

1. Plugs and wires a few months ago(had to be done anyway...100k miles on them) This did not improve the condition.
2. New camshaft position sensor and synchronizer(old synchronizer had destroyed itself)(It is not throwing a camshaft position sensor code anymore.I think I have it set right. This did not improve the condition.
3. New coolant temperature sensors. The one for the gauge used to bury on the hot side on rainy days even though the coolant was not overheated. The other temp sensor is for fuel mixture I heard. This DID improve the condition.

My suspicions:

From reading the forums here the two things I suspect now are either a fuel pressure problem, or a vacuum leak. I suppose the vacuum leak is easiest to check first by spraying carb cleaner around the intake manifold. Does that sound right, or are there better ways to check?

Fuel pressure is simple enough too especially if the parts store has a loaner gauge.

Am I on the right track here, or are there other problems that could cause these symptoms. I will appreciate any and all input.

 

[BigDakota]

Have you changed the fuel filter? A fuel pressure check would be a good idea. A compression check would be a good idea. I say compression test because if a head is cracked or head gasket blown, it would also have the symptoms you described because of the way the engine runs at the different temps you described.
Have you smelled anti -freeze/coolent around your vehicle since this started, especially when its running?

 

[BrooklynBay]

What is the exact engine code that was found? What brand did you use for the new spark plugs & cables? Did you check the firing order to make sure that they didn't get mixed up? Could you add your vehicle, engine, and location to your profile? Did you clean the MAF sensor?

 

[JayT]

Have you changed the fuel filter? A fuel pressure check would be a good idea. A compression check would be a good idea. I say compression test because if a head is cracked or head gasket blown, it would also have the symptoms you described because of the way the engine runs at the different temps you described.
Have you smelled anti -freeze/coolent around your vehicle since this started, especially when its running?

Yesterday I sprayed carb cleaner all around the intake to see if I could detect a vacuum leak, and could not find one. Fuel pressure check is my next step, and I think I should change the filter anyways as it has over 100,000 miles on it. A compression check on all cylinders would be very difficult on this vehicle. I do not smell antifreeze when van is running or not running. There is no white smoke from the exhaust, and the crankcase has no moisture contamination. The coolant is also clean, and does not bubble. I do somewhat suspect a blown head gasket though because I had an overheat when a radiator hose blew on the highway.

 

[JayT]

What is the exact engine code that was found? What brand did you use for the new spark plugs & cables? Did you check the firing order to make sure that they didn't get mixed up? Could you add your vehicle, engine, and location to your profile? Did you clean the MAF sensor?

I'll have to go back to the parts store to get the exact code. I didn't think to ask for it. I will check the brand of the wire and plugs today. I used the firing order from a manual, and it was also stamped on top of the distributor. I will recheck that though. Also the problem did not start when I changed the plugs and wires.. It just did not improve things. I cleaned the MAF sensor before and it did not improve things.

 

[JayT]

Update

Plugs and wires are autolite.
Firing order is correct.

 

[BigDakota]

Did you have the misfire problems before or after the engine overheated?
There are a lot of miles on your current fuel filter, so changing the fuel filter would be wise and a cheap way to eliminate a possible problem or future problems.

 

[JayT]

Did you have the misfire problems before or after the engine overheated?
There are a lot of miles on your current fuel filter, so changing the fuel filter would be wise and a cheap way to eliminate a possible problem or future problems.

I'm thinking I had slight misfire before it overheated, then changed the wires and plugs which did not help. After the overheat the misfire was still only slight but got progressively worse until it stabilized with the current trouble.

I think you are right about the fuel filter. I should change it anyways. I will also try to get a fuel pressure reading. I will update here after I do that.

 

[JayT]

I changed the filter. There does seem to be some improvement, but no cure. I did not check fuel pressure as they did not have a loaner at the parts store. It may be time to sell this thing "as-is", because if it is the head gasket I'm not fooling with it. The van paid for itself the first year. It's a cargo work van in case I never mentioned it.

 

[JayT]

I'm not sure who changed my title but the main misfire problem comes during cruise on level roads and slight inclines. Moderate and heavy acceleration eliminates the problem. All in all, highway speed cruise is where the most pronounced and repetitive misfire is.

 

[JayT]

Update: I ended up getting rid of the Aerostar, but later had the same problem with a Ranger and I traced it to the ignition coil. There are tests you can do on that without removing it. I just wanted to update this because I got a pm back in December but did not see it until today.