502 mag mpi no start
 

I have a 1996 baja 272 with a bone stock 502 mag mpi. It has ran once all season, on Memorial Day. Before the season I did plugs and wires for a general tuneup since I just bought it last year, and ran good last year. Now the one time I had it on the water it was misfiring and would only get up to 1500 rpm’s. Idled it to the dock and checked the wires to see if maybe they weren’t on the right tips on the distributor. Went to start it and got no crank and the cranking battery was arcing on the negative terminal. Went and got some batteries and it would crank forever but did not want to start. Had to get towed in and have been trying to figure this out ever since.

we did find the kill switch to be bad so we bypassed it but still crank no start. Confirmed it has spark and smells like it has fuel and the pump primes when turning the key. Any other ideas? I’m trying to salvage my boating season and I am at a loss with this. Every mechanic is a month or more out and I’m paying for a slip with a non running boat, lol.

Any help is welcome!

It ran ok until you changed spark plugs, now it misses out and won’t restart?
How did you check for spark?

I didn’t run it on the hose before I did anything. Last time it had been started before that was when it was winterized. I checked for spark by grounding out a plug and also with a spark light. Could it be weak spark?

Double check firing order. Easy to cross up wires.
Pull cap and look for carbon tracks on rotor.
(just put a new cap and rotor on if you didn’t)

cap and rotor looked disgusting. I’m surprised it even ran last season at all. Replaced cap, rotor, and coil. Seems to to pop a lot now like it wants to start but still won’t start. At this point the only thing I can think of is the ignition module? That’s the only thing aside from the distributor that I haven’t replaced.

ignition modules will die and do strange things but if you were trying to start it before I would pull and clean all the plugs and they may be so fouled with fuel that it does not want to fire.

what do I need to do for this? Just pull them and let them dry? Or should I spray them down with anything specific

Popping out exhaust or intake?
Put throttle wide open and it should start if flooded.

Did you check the wires are in the correct position on the plugs too? You only mentioned the cap. Your pickup within the distributor may be corroded as well considering how bad you said the cap was.

Now that you have the cap and rotor changed, screw in a new set of spark plugs. They probably got fuel fouled when the cap was bad.

Based on your first few sentences, my guess is you messed up your firing order with the new cap and wires.

Second guess is another wire near the dist cap got pinched or is shorting out and some wiring got fried.

What was the neg battery terminal arcing on??

Sorry, negative on the battery was smoking and throwing sparks. Now I have replaced cap, rotor, wires, plugs x2 and the fuel filter. Still no start. Anybody know where I can connect a fuel pressure tester to? 1996 502 mag mpi

There is a schrader valve in front center of intake, kind of tucked under front of intake.

yeah this thing has me at a loss. It has fuel, spark and compression. Fuel pressure is at 38psi when the pump primes. All cylinders are at 120psi.

It doesn't have spark, if it did there would at least have a backfire

Just rebuilt a 454 MPI and motor was running fine when removed. Tried to start on pallet and no start. Replaced the EST module and it fired right up. Why that happened we have no idea but that's what it was

If you have fuel,spark,and compression it should run. Only stipulation is that ignition occurs close to the correct time. Pull a plug and see if it has fuel on it. Just because you have fuel pressure doesn’t guarantee injectors are firing. How did you check for spark? At the coil or at the plug? Make sure firing order is correct on the cap and follow wires down to plugs. Make sure you used correct rotation when checking firing order.

Have you hooked it up to a computer to check if it is throwing and codes? That would be my first starting point.

If that is the case, there is a good chance you could have fried a bunch of wires and maybe even the battery or ECM.
If the neg cable is getting hot and smoking/sparking, it is not connected well and not grounded properly.