Hi,

I'm looking for help diagnosing the issue with my truck. It has a 5.9 magnum with 205,000km, 46rh recently rebuilt, new spark plugs, wires, cap and rotor. I wired in an external voltage regulator. It has a new fuel pump and new o-rings on the injectors. New O2 sensor, MAP sensor, IAT sensor, and TPS last year and I cleaned the IAC valve. Recently I checked the codes and its giving codes 23 and 25 for the IAT sensor and the IAC valve. So I checked the 4 IAC wires for continuity or shorts and they were fine. I also checked voltages with the just the key on, 2 were 12V and 2 were grounds, as they should be. I was noticing surging at idle a few months ago but now it is fine. The IAT sensor wires had no shorts and there was a resistance across the sensor. And it idles perfectly fine most of the time.

The problem is a missfire only when fully heat soaked and only when accelerating from a stop or low speeds. I'm not sure if it a missfire or something else but the whole truck jerks or lurches forward several times when it happens. They only was to smooth it out is to let off the throttle and apply very light pressure several times. I usually don't drive the truck long enough for the problem to occur, so I forget about it sometimes, but when it does happen it makes it very difficult to drive as every intersection is slow and painful. That is a part of why this problem is so confusing for me. When the engine is cold or just warmed up it runs very well and has lots of power, it takes about 20 minutes of driving before the problem starts. I have had the truck for 2 years and the whole time its had a long crank to start, ~5-7 seconds sometimes (other times it will fire instantly, about 25% of the time), not sure if that could be related somehow. I have also read about setting sync for these engines so I adjusted the distributor slightly in both directions from where is was set and I noticed no changes in the truck after leaving each setting for several days. I have also checked down the throttle body for oil pooling in the intake but there is only a slight film. From what I have read, the intake plenum gasket symptoms are different from what I am experiencing. So now I really don't know what the issue is. Any help is much appreciated.

- Thanks

 

Have you checked for any vac leaks? Have you put a fuel pressure gauge on it to see what the pressure is? The code 23 is "23 Intake air temp sensor out of range". Set the fuel sync, Rotate the crank until you are at TDC #1 cylinder on the compression stroke. Then set the distributor like this...


I suspect the plenum gasket may have a leak because you are in the range. It will continue to get worse so you may want look into repairing it.

 

When the trans was removed/installed, did the crank sensor get damaged?

 

At one point I sprayed brake clean around the intake checking for vac leaks but didn't find anything. I have not checked fuel pressure. I will try setting the sync per your directions. I will also look into fixing the plenum gasket. Thanks for your reply.

 

Not that I know of. I would think if the sensor was damaged the engine would not start or there would be problems all the time. Thanks for your reply.

 

Slightly damaged sensors can give you some strange results.... Wouldn't hurt to check it, even though it is rather a pain....