Won't fire up

[Gus3Gus3]

I have a 91 mighty max automatic. It has spark, I checked the cam, there's fuel. I replaced spark plugs, spark plug wires, distributor cap and rotar and checked the timing and also there's compression so I'm not sure why it's not starting. Can anyone help me out?

[BradMph]

You have just posted everything that should start the truck right up. After reading There should be nothing stopping the truck from running I would imagine. But, as you have found, this is not always the case.
Now you say it has spark and fuel. Have you tried trickling some fuel into carb and see if it will make an attempt to start. If it doesn't it looks closer to a spark problem.
Many times people think they have everything right, but have jumped a timing gear possibly. They end up being 180 off or a tooth or two. There should be no reason why it is not starting if the engine is sparking at the correct time if fuel is being introduced to the cylinders.
So, there is something not doing the job it is suppose to do. This rolls down to the basics and these need to be check even deeper because obviously one of them is failing. Fuel, Spark, Mechanical is as basic as you can get. Start with one at a time and determine it is not the culprit.

Here is a big issue people come across, what have you done to the truck since the last time it was running? This can be as simple as bumping a vacuum line by mistake or kinking a hose or not reinstalling something that was installed before. You need to retrace steps even harder now since your saying that everything is there for it to start, but it is not starting.
Try to dig for more clues on it and present them to us and we will make the best suggestions we can on what we get.

Once again, try the gas in carb thingy, if it doesn't even make an attempt or bark towards starting, I would say that electrical or timing is not correct. If you have things to burn, and fuel is there, then it is not given life from the match (spark).
Fuel pressure could be checked as well if you have fuel injectors there maybe a signal that is not happening. Can you run a system check on the truck? Check codes?

I can't think of anything else right now, your going to have to dig a bit and test a few things to whittle it to the main source.

Keep us updated. and Welcome to the Forum

[pennyman1]

91 ECMs are notorious for bad capacitors - that is most likely the issue - the gas or ether into the intake will tell you for sure. You could also check the fuel rail for fuel pressure to eliminate a dead fuel pump

[Gus3Gus3]

I did try using starting fluid and it still didn't work. I used a compression gauge and everything was right. What I found funny was that it was running right for about two months then the water pump went out and after I replaced it the truck wouldn't start and the water pump doesn't have anything to do with it but after that happened it didn't start anymore. I think I'm going to try the timing again but I'm afraid it might be electrical which I have no clue on and I can't find a diagram where I can possibly start to look at.

[Gus3Gus3]

Thanks pennyman that a pricy part that I think I'm going to have to replace.

[pennyman1]

they are repairable unless the corrosion is really bad on the board.