Tech Help. 7.4 won't start on idle

[Tom Nyeste]

2000 340 Sundancer w/ twin 7.4L 380 H.P. Seized port engine up. Engine was removed and machine shop did a complete overhaul, pistons, rings, brgs,cyclinder heads. Was running perfectly before seizure but after repair would not start on idle circuit. Had to rev to about 1500 to get to catch and run. Installed new IAC and worked fine until next morning start. Back to won't start at idle and hunting (flaring) between 650 and 1500The techs have tried new IAC, new TPS, switched the ECM and wires from good working starboard engine to port. Thought it was the wrong intake manifold or camshaft. Checked and original cam was used. Replaced intake manifold gaskets. It worked for about two hours but would only idle down to 1150. If you flared it , it would drop down to 650 where it was supposed to be. Next day start up and right back to won’t start on idle, hunts (flares) from 650 to 1500.

 

[scoflaw]

20 year old injectors ? Assume you've done all the maintenance, complete tune, monitored fuel pressure

 

[Tom Nyeste]

20 year old injectors ? Assume you've done all the maintenance, complete tune, monitored fuel pressure

Yes and replaced injectors

 

[scoflaw]

Hopefully not those Ebay Chinese knock-offs. Do your sensor values look similar to the good running engine? If it idles high you have an air leak.

 

[PlayDate]

Thought it was the wrong intake manifold or camshaft. Checked and original cam was used. Replaced intake manifold gaskets

Did they use the original intake manifold? It could be cracked. I'm a little surprised they didn't bench test the engine before they put it back into the boat.

Also, what was the cause of the original engine seizing?

 

[Tom Nyeste]

20 year old injectors ? Assume you've done all the maintenance, complete tune, monitored fuel pressure

The fact that one time it will work almost and next start it’s back to hunting and won’t start on idle circuit is really puzzling

 

[Tom Nyeste]

Did they use the original intake manifold? It could be cracked. I'm a little surprised they didn't bench test the engine before they put it back into the boat.

Also, what was the cause of the original engine seizing?

When they did the valve job and work they screwed up putting the remote oil filter back in.

 

[scoflaw]

Fuel pressure is what ? What injectors did you buy?

 

[hottoddie]

Is your 340 one of the boats that required the update exhaust to prevent "reversion"? If so has that modification been made?

 

[Tom Nyeste]

Is your 340 one of the boats that required the update exhaust to prevent "reversion"? If so has that modification been made?

Yes it was updated

 

[PlayDate]

When they did the valve job and work they screwed up putting the remote oil filter back in.

????

 

[Tom Nyeste]

????

?
What was it you are asking

 

[PlayDate]

?
What was it you are asking

I don't know how hooking up a remote oil filter causes the engine to seize.

Part of what you are hearing from the other responders is that oftentimes the real problem is something that happened before or during a rebuilding process. When people post an engine problem.....it is similar to starting in the middle of a book trying to figure out the preceding chapters.

In your case, something is clearing going on with the fuel/air management system. The idle behavior indicates a mismatch between fuel and air which cases the ECM to advance the RPMS. Unfortunately, it can be a number of sensors, the fuel injectors, or an air leak that case the symptoms you are experiencing. It could also be mechanical.

This is one of the reasons most shops test the engine before they put it back into the boat. You have already had them do the smart things by swapping parts to the good motor. But, what remains is the things that were changed during the rebuild.

Injectors would be high on my list depending on where they came from. A bad injector can stick creating a lean/rich condition which causes the ECM to increase rpms. Checking the fuel pressure is easy to eliminate that as a problem source.

The other easy thing to check is what is going on in the ECM. Using a Rinda device will tell you what the ECM sees on the good motor as a baseline and on the problem motor. Hopefully, your mechanic has access to one. The Rinda won't necessarily tell you the problem but may significantly help with narrowing down the possibilities.

 

[Tom Nyeste]

I don't know how hooking up a remote oil filter causes the engine to seize.

Part of what you are hearing from the other responders is that oftentimes the real problem is something that happened before or during a rebuilding process. When people post an engine problem.....it is similar to starting in the middle of a book trying to figure out the preceding chapters.

In your case, something is clearing going on with the fuel/air management system. The idle behavior indicates a mismatch between fuel and air which cases the ECM to advance the RPMS. Unfortunately, it can be a number of sensors, the fuel injectors, or an air leak that case the symptoms you are experiencing. It could also be mechanical.

This is one of the reasons most shops test the engine before they put it back into the boat. You have already had them do the smart things by swapping parts to the good motor. But, what remains is the things that were changed during the rebuild.

Injectors would be high on my list depending on where they came from. A bad injector can stick creating a lean/rich condition which causes the ECM to increase rpms. Checking the fuel pressure is easy to eliminate that as a problem source.

The other easy thing to check is what is going on in the ECM. Using a Rinda device will tell you what the ECM sees on the good motor as a baseline and on the problem motor. Hopefully, your mechanic has access to one. The Rinda won't necessarily tell you the problem but may significantly help with narrowing down the possibilities.

Thank you I’ll pass this on to my mechanic

 

[Tom Nyeste]

Thank you I’ll pass this on to my mechanic

We had picked up the boat after the marine shop had totally replaced the starboard engine and had done heads on the port. We got 20 minutes out and seized the port up. Returned on starboard To the shop and the owner of shop looked in engine bay and remarked that they had screwed up on the remote oil filter. This has been a year long experience. Extremely frustrating.

 

[PlayDate]

We had picked up the boat after the marine shop had totally replaced the starboard engine and had done heads on the port. We got 20 minutes out and seized the port up. Returned on starboard To the shop and the owner of shop looked in engine bay and remarked that they had screwed up on the remote oil filter. This has been a year long experience. Extremely frustrating.

Yikes! If it helps....once you get this sorted out things will get better. 2020 has been a very strange year. Let us know what your mechanic is up to. We are pretty good at second guessing on CSR

 

[Tom Nyeste]

Yikes! If it helps....once you get this sorted out things will get better. 2020 has been a very strange year. Let us know what your mechanic is up to. We are pretty good at second guessing on CSR

Thanks John I will keep you posted.

 

[Tom Nyeste]

Yikes! If it helps....once you get this sorted out things will get better. 2020 has been a very strange year. Let us know what your mechanic is up to. We are pretty good at second guessing on CSR

The tech traded my plenum with the sensors for a unit he had. Included IAC, TPS and MPS I think. Didn’t help. Pulled the injectors and sending them out for testing. I’ll keep you informed

 

[Tom Nyeste]

Hopefully not those Ebay Chinese knock-offs. Do your sensor values look similar to the good running engine? If it idles high you have an air leak.

It surges. 650-1500. They pulled the injectors and are sending them out for testing. Thx Tom

 

[Tom Nyeste]

Yikes! If it helps....once you get this sorted out things will get better. 2020 has been a very strange year. Let us know what your mechanic is up to. We are pretty good at second guessing on CSR

Well it isn’t getting any better. The tech got the injectors back. One was diagnosed as not atomizing at all and another was off by 5%. Replaced both and it started and idled,,,,,,,,until he flared it and right back to hunting and surging. Next thing to check is the camshaft, thinks it may be wrong cam in the supplied block. Will keep you updated. I suppose mentioning that I’m going to burn it on a forum is basically wrong.