View Full Version : 240 EFI Hot Start Problem...

09-26-07, 12:21 AM
The engine in our 2000 Challenger cold starts great. After running it a minute or two and shutting down, it starts even better (warm start?). The problem doesn't show up until we're miles away from the dock and have shut the engine down...

Hot starting does not happen. Once towed back to dock and trailering the boat home (maybe 1.5 - 2 hours) I hook up the hose and it cold starts like a dream.

While trying to hot start, it sounds as if there is no fuel supply to the cylinders...the starter will just crank away without anything firing.

Goes without saying that compression and plugs are fine since I can really haul when I can get the engine started.

The problem here seems to be heat and I'm not sure exactly what the heat would be affecting to cause the apparent lack of fuel.

Can anyone point me in the right direction? I'm either going to have to run the boat all day or take a two hour siesta every time I want to turn the engine off.

Thanks for the help.

09-26-07, 01:13 AM
Welcome Scarfie!....I see your a premium member so it may be to your advantage to go into the manuals and look under the M2 jet drive. That's the manual for your Mercury engine. It has a trouble shooting guide in the Carbs section. The 240 has 2 different set-ups. The fuel injection and carbs. You don't state which one, so I went with the carb set-up.

This system is pretty simple, yet complex. What makes it complex is the sensor's and automatic fuel enrichment valve. It also has what's called the TKS ECM (turn key start electronic control module). I also read a short bit on the carbs bowl and a vapor stop. Which to me seems like a system set up to stop a vapor lock in your fuel system once the engine gets hot. A vapor lock in the fuel system will keep an engine from starting until it (fuel in the carbs) cools off.
I also read about your Fuel Primer. It's an electric fuel pump used to supply fuel to the engine driven fuel pump while the engine is being cranked. It also has a fuel filter on the inlet side. I'd check that too, it may have gone out on you.
The fuel enrichment valve has a button on it that you can push to operate it manually. It says you can push the button for 5 seconds and then try and start. Caution though not to use longer than 5 seconds due to flooding of the cylinders with fuel.

I got you a start here. I hope this helps, but please, help yourself to the M2 jet drive manual in the Premium Members section. You may find it not only a guide to trouble shoot your problem, but a learning tool in understanding how it works..........I found it very interesting!.... :coolgleam:

09-26-07, 09:36 AM
Thanks for the reply Snipe. I got the premium membership so I could download the M2 Jet Drive manual. I spent quite a bit of time scrolling through the 80 + pages last night.

I have the EFI setup, not carbs...sorry you had to write those two paragraphs about the carb setup.

I do believe the engine is overheating. The solid alarm came on this past weekend so i shut it down for the day.

09-26-07, 12:49 PM
No problem, I don't mind writing. Everything I research in here and write about is recorded in forum for others to read. It's a good tool for others that may have that problem. Now, yours. Overheating?

I've looked at your water flow chart in the manual and it's pretty detailed. Have you determined for yourself that the water IS hot? If not, maybe your Engine Head Temperature Sensor is bad. You reading the book too, I'm sure you've read about it too. Check to make sure your water inlet ports from your pump don't have any blockage/restrictions. Your overheat alarm, does it come on after while your flushing with your water hose? It seems you said you ran for a while before the alarm came on........if there was a real problem with your cooling system, you shouldn't be able to run long at all on a V-6 before your over heat alarm.

Let me know what you find out. I'm here if you want to put two heads together on looking for the cause!..............

09-26-07, 03:02 PM
I'm here if you want to put two heads together on looking for the cause!.............. that's awesome...appreciate it

The Head temperature Sensor caught my eye as well. There is another temperature sensor as well (on the engine block I believe. I'll have to dig through and find it again)

NO, the overheat alarm didn't come on while flushing with a hose.

YES, I did run it a loooong time before the alarm came on...at least an hour or more. It makes sense, what you said about a V6 overheating quickly if the cooling system has a problem. That makes me lean further in the direction of thinking it may be a sensor problem.

The repair manual has a very simple diagnostic for the two sensors. I'm going to pull them this evebing to see what I find out. Wish me luck.

09-26-07, 03:05 PM
I wish you all the luck in the world!....that's an awesome engine. I hope you get to the bottom of it.
I did bring up the hose connection with the idea that if it will run well like that and not over heat, then maybe your pick up tube from the pump end has some blockage in it.
With the hose hooke up and on, do you see water coming out of the pump end too? That flow from the pump will let you know that there is likely no blockage there.....

09-27-07, 07:27 PM
Update...we pulled the sensor and according to our diagnosis, it has gone bad. This has me feeling very positive. Also went through the entire cooling system to check for blockage. No blockage found.

Now get this...I didn't mention previously that we just bought this boat last week...the previous owner had installed aftermarket trim tabs. Now, besides his Mickey Mouse wiring job with speaker wire, he mounted the trim tabs directly under each exhaust port in the stern!!!

When the trim tabs are fully retracted, they block BOTH exhaust tubes! Idiot! My cousin who's been helping me (actualy doing most of the work) believes this may be causing vapor lock.

The trim tabs are now off the boat and the wiring has been ripped out as well. I've ordered a new Temperature Sensor from Crowley Marine and i'm jumping out of my skin waiting for it to get here to see if it solves our problem.

Two questions:

1. Do you know of any other place with comprehensive engine part listings like Crowley so i can compare prices in the future?

2. Anyone want a pair of hardly used, well functioning trim tabs?

09-27-07, 08:01 PM
Why in the world would he put trim tabs on it?......
I hope you've solved your problems too!....Not to sure about the idea of blocking the exhaust, causing the vapor lock. If you read the chapter about your carbs, you'll notice there is a feature in the carbs designed to keep vapor lock out. This may be another point of interest for you to read about.
I do hope that the sensor is all that's a problem because when you first reported this problem, it was after an hour or so of running. So lets just cross our fingers and hope that's all it is. You've flushed the system out, so .....go from there.
When you first come into the forum, you'll notice a couple ads we have on our site. They deal in new and used parts. I've ordered from one of them personally and felt like I got a pretty good deal. It was a tool for removing my impellor.......every one else wanted $30 and I bought it through them for $12. I believe it was babits........
I hope to hear your good news when this is all done!...Keep in touch!...:cheers:

10-15-07, 04:05 PM
Not sure why he put trim tabs on although they did help the boat stop porpoising with a light load at certain speeds. He had them set tohelp stop listing of the boat when he was running it alone. He must have been a BIG man.

Anyway, the problem is solved and here's a potential answer for anyone with future problems:

Check any of the following:

Replace plugs with properly gapped new plugs.
Check exhaust and cooling hoses for blockage.
(these two things made a BIG difference in performance. Hot start was still an intermittant problem)

Replace temperature sensor on the induction manifold. A $26 easy replacement. We ran the boat all day yesterday and it restarted any time I wanted it to.

Thanks for the help, Snipe.

07-14-08, 03:01 AM
I have a similar issue with my Merc 240 EFI. Starts fine when cold. Runs fine, 6k RPM 50 MPH. Have had boat for 8 years and love it! This year when it gets hot, it wont start. Starter turns and then releases after a few revolutions. I open engine compartment and while buddy turned key, I slightly opened the throttle plates manually...engine fired and started right away! I have also noticed that my idle RPM is now down around 800-900 RPM.
Could this be a case of vapor lock? Is the low idle setting leaving it too rich to start when hot? Do I have something as simple as spark plugs out of gap range? Or is this a sensor issue?
Thanks for your feedback! Havent looked into the engine manual...yet!