Intermittent no fire issues 1991 7.4l

I see. Yes its tight. Its new with the wires and plugs. Its just stuck on there. When I first had the problem, I was able to pull it off at will. Now it wont budge. I understand that Merc put lock tite on the button originally. They said to crack the button in half to get it off. Which is what had to be done to get the old one off.
 
the rotor can be very tight and hard to get off....but if you use two flat blade screwdrivers on opposite sides of the rotor you can put the blades of the screwdrivers under the rotor and press down on the screwdrivers with equal pressure and the screwdrivers will act like a lever against the distributor body and lift the rotor off the shaft....

cliff
 
Ok. I replaced the ignition coil. Did not solve the problem. I'm gonna replace the module. That's all that is left that I haven't changed. Was going to have it diagnosed. But the marina killed me on replacing both bilge blowers. $678. I think they charged me strictly by the book hours versus actual hours. Hopefully this solves my issue. I will report back in a couple weeks.
 
Thanks Bt Doctur...I did not follow the chart. I didn't have the chart at the time. Plus I'm a little OCD when it comes to tracking down electrical issues like that. But as I mentioned in my first thread, this started two months after I tuned it up. Pick up in distributor was replaced also. It run perfect until it didn't. I bought the module as its the only thing that's not been replaced. Bought wires and more plugs and replaced to see if I had a wire go bad or plug. No change. I wasn't able to change the module. They sent me the wrong one. Prolly should have looked closer at it. It was stamped V-6. My fault. But when I start the motor. After about ten minutes, it runs perfect. And runs perfect all day. Next day on first start up, miss firing again. Till it warms up. Then runs perfect again. I'm going ahead and change the module out. If it doesn't fix the issue, At least I'll have a spare. I'm 4.5 hours away from the boat. Hard to gets parts. I sure hope I don't have a sticky valve. Less than a 1000 hours on motors. Any suggestions? Takes for your input.
 
But when I start the motor. After about ten minutes, it runs perfect. And runs perfect all day. Next day on first start up, miss firing again. Till it warms up. Then runs perfect again.

If I set aside your previous comments about #4 cylinder and focus on this.....it suggests another couple of paths to look at: 1) Stuck or sticking choke 2) Condensation in the distributor cap. Both of these fit the startup symptoms that you are experiencing.

I don't think it is a distributor issue. Using an inductive timing light to diagnose a cylinder not firing is not reliable. A spark tester is if the engine is running.

What you describe seems much more likely to be a carb problem rather than ignition.
 
Ok. Replaced control module. Did not solve the problem. I check the choke. It appears to be working properly. I'm at a total loss of what to do next.


how did you check the choke and how long did it take to open the carb plate all the way?......

cliff
 
Well, I checked it cold and it was about a quarter open any way. I really just checked to see if was stuck. It move freely. Actually now that I think about it. Shouldn't there be some resistance when pushing it open? It moved real easy.
 
Well, I checked it cold and it was about a quarter open any way. I really just checked to see if was stuck. It move freely. Actually now that I think about it. Shouldn't there be some resistance when pushing it open? It moved real easy.


yes it should have resistance.....it should be connected to a coil spring inside of the round housing....the coil spring should have a wire going to it....you can watch the carb plate when you turn the ignition switch to the 'run' position without starting the engine....when the engine is cold the plate should be nearly all the way closed....with the key on you should start seeing the plate slowly start to open...the wire is supplying power to the spring causing it to heat up and expand...as the spring expands the carb plate opens up until it is fully open...

cliff
 
Hi guys. Update. I haven’t posted anything in awhile. Because I haven’t done anything. But I had a merc mechanic come look at this motor. His initial thought was the carb needs rebuilt. He took both and rebuild them. ($500). That didn’t solve the problem. Now he thinks the riser is bad and leaking water in the cylinder. I researched the risers functions. It seems reasonable that the riser could be bad. It’s obviously not a big leak or it would hydrolock. Could the intake manifold also leak into the cylinder? Any thoughts on his diagnosis?
 

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