1992 3.0L Mercrusier - misfire over 2200 rpm

[pbl]

Hello all,
I am new to this forum and have I am having issues with my 1992 3.0L, EST distributor Merc. misfiring when over 2200 RPM. A little history - I was cruising across a lake at 4000 rpms and then the engine started to miss, about 10 minutes later it died and I was not able to restart. It has an EST dist. and this is the work I've done since, but to no avail. I changed the Ign. coil, spark module inside the distributor, spark plugs, cap and rotor, checked plug wires, (3000-5000 ohms depending on length), checked the pick up coil - ok, it was right in middle of specs. I can start the engine but it runs a little rough and will not rev over 2200 rpm without misfiring and popping in the carb. I pulled the fuel filter in the pump ( to eliminate the filter) and ran external gas source to eliminate the fuel tank. still the same. I didn't see any fuel in the clear rubber line from the fuel pump to the carb indicating a bad fuel pump. What am I missing - could it still be a defective fuel pump? Any help would be appreciated. Thanks

 

[QBhoy]

Hi. Good chance that you’ve taken bad fuel through it, with water affecting its quality. Having no water separating filter on these, an easy thing to happen. Despite the basic filter in the pump being visibly not appearing bad…they aren’t designed to mitigate the risk of water. So what’s happens…8/10 times…is that the carb becomes compromised and has to come off for a clean. So despite running off a remote fuel tank…things still don’t get any better, just with the carb having been affected by events previously. That’s where my money is at.

 

[Scott Danforth]

It's never the coil

Have you verified timing?

Change the fuel filter and empty the contents of your fuel filter into a clear container and check the contents. If you have water in the fuel, you will see

 

[pbl]

Thanks for the replies. I had removed the filter earlier and there was no evidence of water in the bowl of the fuel pump. I will remove the sending unit in the tank and see if I can see any water present. I am also going to pull the top off the carb and see if any water is sitting in the bowl. One other thing I forgot to add to the history of this issue is when I tried to start it and it wouldn't start, I checked for spark with a timing light and had nothing - that is why I replaced the coil. I still had no spark so I replaced the pick up module. After replacing the module, it would start but I couldn't get over 2200 rpm without it misfiring and popping. This is when I changed the dist. cap and rotor thinking it was defective, but no change. I'll see if there is water in the carb; if there was water, wouldn't it just work it's way through after I put on the remote tank? Thanks again!

 

[Scott Danforth]

Have you verified timing

 

[QBhoy]

Thanks for the replies. I had removed the filter earlier and there was no evidence of water in the bowl of the fuel pump. I will remove the sending unit in the tank and see if I can see any water present. I am also going to pull the top off the carb and see if any water is sitting in the bowl. One other thing I forgot to add to the history of this issue is when I tried to start it and it wouldn't start, I checked for spark with a timing light and had nothing - that is why I replaced the coil. I still had no spark so I replaced the pick up module. After replacing the module, it would start but I couldn't get over 2200 rpm without it misfiring and popping. This is when I changed the dist. cap and rotor thinking it was defective, but no change. I'll see if there is water in the carb; if there was water, wouldn't it just work it's way through after I put on the remote tank? Thanks again!

Just in reply to your last sentence…no. Not if the carb was now compromised. Very common.

 

[markhodges78]

I replaced the pick up module. After replacing the module, it would start but I couldn't get over 2200 rpm without it misfiring and popping.

By chance did you replace it with an aftermarket module? reason I ask is I have not had much luck with aftermarket modules for some reason they just don't want to advance the time as they should..

 

[tank1949]

Hello all,
I am new to this forum and have I am having issues with my 1992 3.0L, EST distributor Merc. misfiring when over 2200 RPM. A little history - I was cruising across a lake at 4000 rpms and then the engine started to miss, about 10 minutes later it died and I was not able to restart. It has an EST dist. and this is the work I've done since, but to no avail. I changed the Ign. coil, spark module inside the distributor, spark plugs, cap and rotor, checked plug wires, (3000-5000 ohms depending on length), checked the pick up coil - ok, it was right in middle of specs. I can start the engine but it runs a little rough and will not rev over 2200 rpm without misfiring and popping in the carb. I pulled the fuel filter in the pump ( to eliminate the filter) and ran external gas source to eliminate the fuel tank. still the same. I didn't see any fuel in the clear rubber line from the fuel pump to the carb indicating a bad fuel pump. What am I missing - could it still be a defective fuel pump? Any help would be appreciated. Thanks

It is hard to believe that you don't have a water/fuel filter separator. You didn't mention it? Fuel tanks are moisture magnets.

 

[pbl]

Update,
So I pulled the sending unit and checked inside the tank. It was surprising clean, especially after 30 years. The pick up screen and anti-syphon valve were good also. As Scott suggested, I checked the timing and it was at 0 degrees at an idle. I increased the rpm to 2100, just before it starts to pop and the timing was still at 0 degrees. I shunted the two white wires and rechecked it and found that the timing didn't change. I loosened off the dist. and ran engine at 2200 rpm and it started to pop, I then advanced the timing manually by turning the dist. to mechanically advance it and increased to 4000 rpm and ran smooth. As Mark suggested, the pick up module could be the issue as I did purchase an aftermarket module to try and keep costs down. This being said, is there a supplier of modules that aren't as pricey as an OEM module but still work properly? Thanks to all that replied.

 

[markhodges78]

Update,
So I pulled the sending unit and checked inside the tank. It was surprising clean, especially after 30 years. The pick up screen and anti-syphon valve were good also. As Scott suggested, I checked the timing and it was at 0 degrees at an idle. I increased the rpm to 2100, just before it starts to pop and the timing was still at 0 degrees. I shunted the two white wires and rechecked it and found that the timing didn't change. I loosened off the dist. and ran engine at 2200 rpm and it started to pop, I then advanced the timing manually by turning the dist. to mechanically advance it and increased to 4000 rpm and ran smooth. As Mark suggested, the pick up module could be the issue as I did purchase an aftermarket module to try and keep costs down. This being said, is there a supplier of modules that aren't as pricey as an OEM module but still work properly? Thanks to all that replied.

I'm glad you figured out the problem I think after trying a few different after market modules I ended up getting a oem to replace it with..