New engine: running cold and misfiring.

[loco]

Hi all,
I've had a new Repower Marine (GM vortec 4.3L V6) installed and got it running today. The engineer set the initial timing to 2 degrees at idle using the tool you plug into the distributor as per the manual. They were unable to take the boat out for a test run as conditions were terrible but said it sounded a little lumpy.

So, today I tried to take it out, but had a couple of issues. First off, the engine seems to be running very cold and not getting up to temperature. 10/15 mins at fast-ish idle and the temperature gauge is barely registering. Using an infrared temp sensor, the inlet manifold sits at a steady 33C (91F).
Curiously, the temperature at the top of each of the exhaust manifolds differ by about 10 degrees, too.

I spoke to the engineer who suggested maybe putting the engine under a little load might bring up the temp so we gently went out of the harbour and brought the revs up a fraction. At about 2000rpm there was a bang and the engine backfired through the carb, so we quickly returned it back to harbour.

So, it seems the timing is well out. I've got a non-adjustable timing gun - is it possible to check and set the timing without the tool/cable that I believe bypasses the electronic spark timing of the engine?
Also, could very off timing cause the engine to run so cold? If not, any suggestions? I'm thinking the thermostat might be stuck open, but wanted to check before taking things apart.

Any help greatly appreciated!

 

[Don S]

Re: New engine: running cold and misfiring.

Well, 91? is way too cold. Obvious answer is the condition of the thermostat. New doesn't mean it's installed correctly or working.
So now, we need information.
What was it before the re-power? Is it a full complete engine repower, or just a new long block? Year, carbed or MPI, what ignition system, raw water cooled or closed cooling? What outdrive? Pictures.

 

[loco]

Re: New engine: running cold and misfiring.

Well, 91? is way too cold. Obvious answer is the condition of the thermostat. New doesn't mean it's installed correctly or working.
So now, we need information.
What was it before the re-power? Is it a full complete engine repower, or just a new long block? Year, carbed or MPI, what ignition system, raw water cooled or closed cooling? What outdrive? Pictures.

thanks, Ok. Before we had an AQ205a. It was pretty rotten so we replaced the whole unit with a parpac from repower. It's the carbed engine, and we have it fitted with the bell housing from the AQ205a and mated to our original DP290 drive.

We had the pulleys from the original engine powdercoated and fitted, and we're also using the power steering pump & flywheel from the original. Everything else is new. It's raw water cooled and the sea temp right now is a touch over 10C (50F). We kept the mercruiser style thermostat housing instead of going back to the aq205a's as the engine supplier said it had larger hoses so was a bit better.

It's got a holley carb and I believe a delco ignition.

This is the manual we've been running from which suggests just a 2 degree advance:
http://marinepowerusa.com/pdfs/MarinePowerUSA_Engine_Owners_Manual_Pre-2011.pdf

I don't have any detailed photos of it at hand other than this one from when the engine was originally dropped into thge engine bay and before it was plumbed in. I'll get some more photos today:


Thanks in advance.

 

[Don S]

Re: New engine: running cold and misfiring.

I would start with the thermostat, see if it's stuck open. While you have the thermostat housing off, make sure there isn't a bypass hole in the housing somewhere that lets water to the exhaust system before the thermostat opens. They usually aren't a large hole on other models, and when they get plugged you can get over cooling.
No need for more pictures, that one shows the necessary items along with the manual.

Timing is supposed to be 2? according to the manual, and yes you need to tool to set the timing into base timing mode before adjusting.
The back fire could have been from idling for a long time, and running a little lean. If it happened during acceleration.

You need to get it out and do some testing on the water, and get it up to some rpm and find out what's going on.

 

[loco]

Re: New engine: running cold and misfiring.

Ok spent some time on the engine today:

- The cooling issue was due to the thermostat. There's a plastic cylinder that holds the thermostat up against the top which had slipped down. This allowed water to bypass the thermostat. We took it apart and used some marine adhesive to prevent it slipping down in the future. Now the engine warms up and sits at a constant 62C, so all good there now.


- I checked the timing, but I've got a non-adjustable timing gun and do not have the tool to plug into the distributor. However, it seemed to have zero degrees of advance as it stands, so it really looks like that's the issue here. The engineer is going down tomorrow to go over the settings once more. I'll post an update.

Cheers

I would start with the thermostat, see if it's stuck open. While you have the thermostat housing off, make sure there isn't a bypass hole in the housing somewhere that lets water to the exhaust system before the thermostat opens. They usually aren't a large hole on other models, and when they get plugged you can get over cooling.
No need for more pictures, that one shows the necessary items along with the manual.

Timing is supposed to be 2? according to the manual, and yes you need to tool to set the timing into base timing mode before adjusting.
The back fire could have been from idling for a long time, and running a little lean. If it happened during acceleration.

You need to get it out and do some testing on the water, and get it up to some rpm and find out what's going on.