Backfiring Engine under load

[OcoeeSki]

Like Paxdad I feel your pain, very unfortunate. I belive you said the rebuilder installed the distributor? If so I hope they do the right thing, I would probably have to have a few stern words with them. Something is not right when you do that type of damage right off the bat, incorrect cam, incorrectly installed, bad oil pump, bad distributor, who knows until you take it back apart. Good luck with it, let us know what you find out.

[davebuc]

So I am up and running now.

Short story-it was the firing order. My cam was NOT cut for the "more mainstream" firing order.

Here is the longer report:

The teeth that coming off the distributor did not damage the cam (whew).

I'm very busy w/ work so I had a shop put the engine in, do shaft alignment, etc.

At the first lake test, it did exactly the same thing. Backfired @ 1200RPM, and had very little power.

With the engine on, in neutral, we disabled the wiring harnesses from the fuel injectors one at a time, and discovered that 4 of the 8 cylinders were not firing (no rpm or engine sound change when the injector was unplugged). Then the mechanic goes home for the weekend.

I tell a friend of mine about our lake test. An hour later, he comes back to me and says "Aren't there 2 firing orders that exist for that engine? What if the cam was cut for 15426378, BUT was packaged in a box for the more mainstream firing order 13726548." When you line up the firing orders, there are 4 cylinders in common for the different firing orders. I immediately noticed that 3 of the cylinders that weren't firing could be explained by this theory, and couldn't remember which other cylinder was missing.

First thing Monday morning, I go to the engine builder and mechanic and offer this theory. They both think it is unlikely.

The mechanic pulls apart my fuel system, believing the problem is somewhere in fuel. He finds my fuel injectors to be each in various states of clogged with sand, metal shavings and junk. So we do new injectors.

The next time we fire the engine, it still is missing. The mechanic decides to switch the plug wires to the other firing order. The engine builder was there for this. He fires the engine. It sounds amazing. Mechanic and builder are both sufficiently surprised.

They set the timing.
We go to the lake. Lake Test= success.

So, I now have a new ignition sensor, coil, fuel injectors, throttle position sensor, & idle air control valve. Most of these parts weren't the problem. The boat is now running great with my old distributor.

It turns out the shop that made and shipped the cam believed if they cut it for 15426378, it would give more low-end torque. The same crank is used in either case. This cam isn't available in the catalog, so the guy who took the order, requested a custom, but didn't tell the engine builder, AND shipped it in the box with the part number for a cam that would use the OTHER firing order.

Wacky.
So, I lost boating days, time and money because of poor communication.

At least I am up and running now. WooHoo!

Dave