[jbjustin]

1989 C3500 with 7.4L 454 Big Block

Did a head gasket job and now the truck runs poorly.

Truck does idle but very irratic, sounds almost like an aftermarket cam was installed. Seems to almost stall and then it catches itself. Truck is driveable but has a severe loss of power. Truck would spin the tires off the line with bad head gasket, barely spins the tires in the dirt now. I have set the timing to 4* like the sticker says.

The exhaust is very hot and has strong fumes, cant stand too close or it starts to burn your eyes.

No water in oil like before the head gasket job.
Spark plugs new, checked and have a nice color to them, doesnt seem to be burning any water.

Not sure what to do here, exhausted from the head gasket job and just want my truck running to pull my toys around.

Thanks,
JB

 

[Revredneck]

Did you unplug the "set timing" connector when you set the timing? Are both injectors spraying fuel into the throttle body? Do you have a vacuum leak somewhere or a bad computer ground? These are the kinds of things I'd be looking for.
Good Luck and God Bless

 

[jbjustin]

I did set the timing with the "set timing" connector unplugged. I took it to a shop yesterday and they told me the computer was fried. They said the truck is running as if the MAP sensor is bad, but replacing with a new one did nothing. They hooked a scanner to it to check sensor voltages and what not, but the computer was unresponsive with any feedback.

Both injectors spray fuel. No detected vacuum leaks. Could be the computer ground. I will look into that. Do you happen to have a wiring diagram or know where the computer ground would be?

Thanks.

 

[BobEhud]

this could be so easy.check your firing order.

 

[terryny]

I hope they had a spare map sensor and only used it for test purposes. To be suspicious of the map sensor and replace it on your pocket book BEFORE plugging in the scanner would be terrible... If these events are accurate I'd question their abilility to diagnose a computer.

After you try what is already posted, I'd be quick to check the valve timing. If you can muscle the crank by hand... feel how much slop is between the crank and cam by judging the free-play while rotating slightly in the normal direction (just to take up any slack) then the opposite direction. Keep us updated.

 

[jbjustin]

Ok, the shop is owned by my uncle. He bought the map on his dime.

I took the truck to an electrical shop today and they were able to get the computer to read, but they said they couldnt help me out with my problem. They didn't charge me anything and sent me on my way. The codes that came up were 33 and 34. Both are for MAP sensor, low voltage and high voltage, which is weird. I'm stuck on what to do and really do not want to convert to a carb and HEI distributor.

As far as valves go, I did exactly what ALLDATA said to do when I replaced the head gaskets.

 

[terryny]

If you keep getting both map sensor codes... after clearing the codes... the ECM (computer) is probably at fault. Thoroughly inspect the wiring to the sensor!

To clear the codes disconnect the negative battery cable. To check the codes insert a paper clip/or,etc between the A & B terminals on the ALDC... turn the key on and count the flashes.