Pulling my hair out, engine misses at 4K...
08-13-2007, 06:37 PM
#1
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Thread Starter
Pulling my hair out, engine misses at 4K...
Engine: Single 502 with B&M 250 blower. Crane ignition base at 10 total 30.
Vacuum / Boost are steady, fuel pressure is 9 at all rpm.
Symptoms: Breaks up and sort of misses in neutral at 3K, runs OK on the water to about 4K or so then starts a burbling miss. Sort of sounds like it the ignition is breaking up. Earlier this year ran WOT just fine. Problem is gradually getting worse in that it breaks up sooner. First noticed it during a WOT run sort of sounded like hitting the rev limiter but now stars breaking up earlier.
What I have tried: New AC MR41T spark plugs, cap and rotor and Taylor 8.0 mm spark plug wires. No change in symptoms.
Changed ignition system back to stock Merc with V6 ignition module. Base was at 20 total 30. No change in symptoms.
Swapped to different distributor (different pickup in spare distributor). No change in symptoms.
Back to Crane ignition systems with the spare distribuitor, still breaks up. Put original distributor back in (this had had new pickup several years back). Ran a new purple ignition wire from harness back to box, fresh ground wire to Crane coil and distributor. Checked power connections and grounds. No change in symptoms. I don’t really think it has anything to do with the Crane system as when I went back to the stock Merc stuff no similar grounds or power feeds were used and the coil was different.
Not sure where to go from here. Perhaps disconnect Tach? Something in the alternator? Grasping at straws now.
Any suggestion would be helpful.
Tim T.
Vacuum / Boost are steady, fuel pressure is 9 at all rpm.
Symptoms: Breaks up and sort of misses in neutral at 3K, runs OK on the water to about 4K or so then starts a burbling miss. Sort of sounds like it the ignition is breaking up. Earlier this year ran WOT just fine. Problem is gradually getting worse in that it breaks up sooner. First noticed it during a WOT run sort of sounded like hitting the rev limiter but now stars breaking up earlier.
What I have tried: New AC MR41T spark plugs, cap and rotor and Taylor 8.0 mm spark plug wires. No change in symptoms.
Changed ignition system back to stock Merc with V6 ignition module. Base was at 20 total 30. No change in symptoms.
Swapped to different distributor (different pickup in spare distributor). No change in symptoms.
Back to Crane ignition systems with the spare distribuitor, still breaks up. Put original distributor back in (this had had new pickup several years back). Ran a new purple ignition wire from harness back to box, fresh ground wire to Crane coil and distributor. Checked power connections and grounds. No change in symptoms. I don’t really think it has anything to do with the Crane system as when I went back to the stock Merc stuff no similar grounds or power feeds were used and the coil was different.
Not sure where to go from here. Perhaps disconnect Tach? Something in the alternator? Grasping at straws now.
Any suggestion would be helpful.
Tim T.
08-13-2007, 07:04 PM
#2
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If your tach has any flutter it could do that. Have you tried a purple jumper from coil to battery? Check you kill switch at dash by pass to test if using purple wire. New coil wire with plugs?
Jim
Jim
08-13-2007, 07:07 PM
#3
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Thread Starter
No flutter in the tach.
New coil wire with wires. I thought about jumping a hot lead staight to the coil or comparing with DVM battery voltage to voltage at coil. They should be the same?
New coil wire with wires. I thought about jumping a hot lead staight to the coil or comparing with DVM battery voltage to voltage at coil. They should be the same?
08-13-2007, 07:14 PM
#4
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I just went through almost the exact same problem in my ski boat. It would start to miss at about 3400rpm's and I thought it was ignition. The problem gradually started to get worse. Everything checked out fine. It was driving me nuts. I finally concentrated on the fuel system and pulled the carb. Sure enough an air passage was plugged on the 4 barrel side and was causing a slight lean stumble. Gave it a good cleaning and new gaskets and the problem was FINALLY solved.
Darrell.
Darrell.
08-13-2007, 07:25 PM
#6
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Thread Starter
I suppose I can pull the carb and give it a cleanup. I would expect a lean condition to pop. New fuel filter and a carb clean up tommorow. Run jumper to Crane box to bypass key switch, and lanyard plus 20 odd feet of harness and the harness plug. Crane makes mention of using a filter capactor on the main power to the box so perhaps a trip to Radio Shack is
08-13-2007, 07:59 PM
#8
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iTrader: (1)
I suppose I can pull the carb and give it a cleanup. I would expect a lean condition to pop. New fuel filter and a carb clean up tommorow. Run jumper to Crane box to bypass key switch, and lanyard plus 20 odd feet of harness and the harness plug. Crane makes mention of using a filter capactor on the main power to the box so perhaps a trip to Radio Shack is
Not always. Engine on dyno was breaking up so bad we chased ignition problems that wheren't there. No carb hicup/backfire. Hooked up wideband and engine went to 16:1 and + A/F. It was fuel related, not ignition. Man, did it seem like ignition.
My Crane box came with a capacitor in it. Take a look in your box - I believe it is blue colored. If you don't have it I may possibly still have one that I didn't use. Let me know if you want me to dig for it.
08-13-2007, 08:12 PM
#9
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Thread Starter
SB,
What does the cap look like? I bought my Crane box used so it was not there. The manual states something like 38,000 uF 16v. About how big is this, I bet I can get one at a local electrical shop. I would not suspect the missing cap as a problem since I have been running this box years with no issues but if one is supposed to be there I will get it in place.
What does the cap look like? I bought my Crane box used so it was not there. The manual states something like 38,000 uF 16v. About how big is this, I bet I can get one at a local electrical shop. I would not suspect the missing cap as a problem since I have been running this box years with no issues but if one is supposed to be there I will get it in place.
08-13-2007, 08:26 PM
#10
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Thread Starter
Well here is a 50,000 uF cap for 20 bucks.
How is it hooked up? Between ground and hot or what? Been a few years since HS electronics. I don't suspect this will solve my problem but I have another issue with the stereo cutting out that may be related to this.
How is it hooked up? Between ground and hot or what? Been a few years since HS electronics. I don't suspect this will solve my problem but I have another issue with the stereo cutting out that may be related to this.
