2001 350 MPI Stalling and Slight misfire

"I was posting on this website

"I was posting on this website a few months ago after having major problems with a repower to htis engine. it had a major misfire from about 2000rpm upwards. that is now mostly fixed.

The engine now stalls for no reason at idle rpm. it has a new IAC valve and I tried exchanging the old one. it has had a scan tool on it and no faults.

It also has a slight intermitent misfire from about 3000rpm up where it will drop 300rpm or so in an instant then return.

this is a vast improvement from what it was, but is still not right. The biggest thing that was the fix of th emajor problem was rewiring the main battery wires and getting rid of some live open end wires.

That said, I was looking over it all today again for the 500th time and noticed two things that could be big issues or non issues.

1. when I removed the air filter/flame arrestor, I noticed that there is a hesian type material stuck in the throttle body. this was in the port where the IAC vale line enters the throttle body. My assumption is that this would restrict air flow from the IAC and could act to lower the revs? Should this even be there? and why would it be there if its not meant to be there. it looks like it could break up and enter the engine

throttle body"">

its the tan colour stuff in the back right port

2. this could a a major or minor issue. There is a large earth wire on the block at the back right hand end near the bull horns or Y manifold. Problem it this wire has been cut and left there 6 inches from where it is bolted on. I'm not sure if this was done when it was rewired and they did an alternative, but it does not look right that a big earthwire such as this has been cut. and where should it go to?? I would have though it would not even run if this was an important wire

Any ideas.

with the improvement we had with the rewiring I am assuming the problem may be wiring somewhere still."

"I'm no boat mechanic but

"I'm no boat mechanic but just guessing?

have you tried starting the engine with the air cleaner to the IAC valve off to make sure its opening( big sucking sound with the filter off)?

checked base timing?

checked there is no air getting into the fuel rail?

would check with who rewired boat about ground, could go to engine,garboard drain, mercathode etc."

"Chris the comment "when I

"Chris the comment "when I removed the air filter/flame arrestor, I noticed that there is a hesian type material stuck in the throttle body. this was in the port where the IAC vale line enters the throttle body" that is called an IAC muffler, it is about 1.50, or less, if removed the IAC may not operate properly and may be the cause of the stalling at low RPM. Replace it."

"Chris, Look at this diagram [

"Chris, Look at this diagram http://www.perfprotech.com/store/assembly/THROTTLE-BODY,8094-70.aspx"

"I have talked to the mechanic

"I have talked to the mechanic I had and they did replace the IAC muffler part. I had them run the computer on it the other day and they made the comment on my Bill that it had high intake pressure. Anyone know if that is a cause or symtom of the problem?? Also when I run it at about 1000-1200 rpm in neutral the revs fluctuate up and down a bit.

The earth wire looks like it was from the old installation going to he power steering pump so nothing there.

I was talking to my electrician and he quizzed me on if water is getting into the electrics anywhere. I did find a leak on the weekend from a windscreen screw hole that is leaking right onto the cables heading up to the helm. although would that be the cause of the problem if its not getting wet there at the time?

I note that I had previously reduced the gap on the spark plugs as advised on this and another website, so I think I now have to regap the plugs to the correct setting. not sure that will have any effect though??"

"hig intake pressure = low man

"hig intake pressure = low manifold vacuum? Look for split/cracked hose or something loose. A vacuum gauge test would also help in assessing overall health of the engine, particularly the top end.

As far as the unterminated wire, probably best to trace the other end to see where it goes. If it turns out to be a 'leftover', just remove it."

"I had a look around all the h

"I had a look around all the hoses and all looked ok. I changed the plug gap back to the factory spec and ran it on the hard stand and it didn't stall but was definatetly not smooth and it appears to be a fraction slow. I took off the distributor cap and noticed some black marks on some of the pins and the others are clear. I remember being advised in my earlier thread of problems with these dizzy caps with bad tolerances. can that cause the intermitent misfire. the mechanics I have had on it have not made any mention of it so I suspect its not a major. I know when it was running really bad early on they did try a complete alternative distributor. but now that its almost right I wonder if that can be causing anything. I also noticed a couple of sparkleads resting on the starter motor main cable, which probably wasn't good so I moved that around.

here is a picture of the dizzy cap. I gave the pins a bit of a scrub. is this much of an issue??
dizzy cap