240EFI low idle/major smoke/won't start when warm

[daveo150]

Hi all,
So I've done a bunch of searching on this on the forums here, and I've found a lot of info, so here's what I have going on....
So I have a 2001 Challenger 1800, that had a blown engine when i got it. Replaced with a reman short block in 2008.
Was running well after rebuild.....only noticed the traditional startup smoke (due to the enrichment) that would clear up after starting.
Boat doesn't get many hours of runtime per year, then winterized until next year. I've been fighting water in my gas, but the addition
of a secondary 25um filter seems to have finally cleared this problem for me.

So, here's what's going on....
Cold start: engine will start fine, but runs low rpm (maybe 500-700). It appears to idle ok (but low), then the smoke starts increasing and the engine sounds like it's loading up and getting flooded out....once i get it in forward I can increase the throttle to about 2000-2500 and the smoke clears up and she purrs just fine. Good acceleration, no hesitation, good top speed. So, then I'll idle back down and the same symptoms begin.....low idle, the smoke starts increasing, and it may finally stall out. If it stalls out, she won't restart when hot.
Let it cool, she'll restart.

I've read several posts describing very similar symptoms on their 240EFI, and it seems the usual suspects are:
- port side temp sensor
- TPS sensor

I see posts about the problem, but few followups on what actually SOLVED the problem for you.
Can anyone chime in if they know what the most likely culprit has traditionally been here?
I haven't been able to test my temp sensor (will probably just replace) or the TPS sensor (my god WHY is that SO expensive?!?).

Any insight is greatly appreciated!
Thanx!
Dave

 

[Dr Honda]

I would start with a few things.

1) Check the Port side temp sender.

2) Check the TPS. (and hope it's ok)

3) Check the compression.

4) Check for spark on ALL plugs.


I'll assume that #3 is OK... but it's always a good data point to have. Then... in the future... if you notice a drop... you may be able to do a rebuild before you get a melt down. (much cheaper to replace pistons and rings, if you don't break parts)


BUT... with the RPM's being so low... it could be a dead cyl or two. Not from damage... but from lack of spark. If you have 2 plugs not firing... the idle will drop. AND, in turn... it will feel like it loads up faster.


Now... if your ECU sees that the temp sender, or the TPS has gone bad... it will go to "Full Fuel". That will also drop your idle RPM's, and make a lot of smoke. BUT... it doesn't effect "Full Throttle" fueling. (just the low RPM trim)

As far as "Why is the TPS so expensive"... well... it's simple. There isn't any other engines in the word that use it. It's a 12K ohm pot. Most cars use a 4K to 6K TPS. I found one in a jag that was mechanically the same... but the wrong value. If you have issues with the electrical system... it's truly cheaper to make this engine run with a stand alone computer. (something like a mega squirt)

Anyway... check those 4 things, and let us know.

 

[daveo150]

Thanx Dr. Honda.....I've noticed you're usually the one who replies to these questions!
I just replaced all 6 plugs, and admittedly i didn't notice any 'vibration' that might be typical with missing cylinders....
Do you think it could still deliver top speed with 2 cylinders out?
I just ordered the replacement 13536A14 temperature sensor. I didn't bother to check it yet but it's cheap
enough to just replace. Plus i read the stick thread up top and that seemed to suggest this was almost a 'consumable' part.
I will attempt to test the TPS too...but here hoping it isn't that. :cheers:
Thanx!
Dave

 

[Dr Honda]

no... you wont get top RPM with 2 dead cyl's. It will be a solid 1000 to 1500 rpm's low. But... you could get some that are intermittent when the RPM's are low. (like at idle) The charging for the coil packs could be effected if the stator is going bad.

Yes... the port side sender is almost disposable. It's not like it fails constantly. But on these boats... once they reach 10 years old or so (so the last 5~6 years) it's been a common issue. I wasn't having issues... but I replaced mine after my rebuild "just because". But, since my old one was OK... I threw it in the tool box with the extra spark plugs.