Tachometer and ignition problem ?
07-28-2005, 10:47 AM
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Location: Knoxville,TN, USA
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Tachometer and ignition problem ?
I've had a problem for over a year and have posted here twice for the same problem with no solution so far. I have had several very good suggestions as to fix this but none have fixed the problem. Briefly, here's the problem and a new question for someone who might have some experience here.
I'm listing engine specs hoping it will possibly aid in diagnosis.
Engine specs: Totally rebuilt in 2002, 1996 Gen V 502EFI's with all HP mods including Crane cam, Crane roller lifters, Crane roller rockers, springs, retainers etc., Inconel Exhaust, Manley SS intake, mild head work, J&E Pistons, 8 qt pans, Stainless Marine exhaust w/long thru transom risers, ECM reprogramming.
Once again, here's my problem:
My starboard engine will stumble and stutter badly just off idle as I start to plane ( not at all at idle ) and until I advance the throttle slightly past a certain point. It will catch up to the other engine and be perfectly smooth. If I move on up to 3500 RPM to cruise, usually within a few minutes the starboard tach will flicker a little and settle back to 3200 RPM. It's not just the tach, I lose power and speed. At that point I have to advance the throttle another notch to get the engine back to 3500 RPM. While under this condition the engine will only run up to about 4000-4100 RPM at WOT. Normal WOT is about 5200 RPM. Here's a strange phenomena I've just recently noted ! If I only advance throttle's to 3200 RPM, I can cruise seemingly all day without a glitch. I never get into the tach flicker or lose power at all. I can throttle to WOT from 3200 and get full RPM.
Here's what I've tested so far. Fuel pressure under way remains +/- 2 lb @ 33 lbs measured from the front of the engine. I experienced a VST screen problem early on with these VST engines but that problem was solved long ago with the addition of RACOR filters after the standard Merc water seperator fuel filters. Plugs and plug wires have been replaced. Distributor cap replaced. Computer hookup seems relatively useless to find this problem as far as I've been told.
I have Gaffrig tachs that were installed when the engines were built. Is it possible that a problem with a tach cause a problem of this sort ? After all, the ignition goes directly to the tach. I will be swapping the tach positives this weekend to see if the problem moves with the tach. I'm not very optimistic of this being the problem but am hopeful.
Anyone ever heard of a tach causing an engine problem of this or any other type ? With the tach flicker, it seems an electrical problem. Does anyone agree with that ? I'm getting very weary of this problem that no one seems to be able to pin point.
Help ! Please !
I'm listing engine specs hoping it will possibly aid in diagnosis.
Engine specs: Totally rebuilt in 2002, 1996 Gen V 502EFI's with all HP mods including Crane cam, Crane roller lifters, Crane roller rockers, springs, retainers etc., Inconel Exhaust, Manley SS intake, mild head work, J&E Pistons, 8 qt pans, Stainless Marine exhaust w/long thru transom risers, ECM reprogramming.
Once again, here's my problem:
My starboard engine will stumble and stutter badly just off idle as I start to plane ( not at all at idle ) and until I advance the throttle slightly past a certain point. It will catch up to the other engine and be perfectly smooth. If I move on up to 3500 RPM to cruise, usually within a few minutes the starboard tach will flicker a little and settle back to 3200 RPM. It's not just the tach, I lose power and speed. At that point I have to advance the throttle another notch to get the engine back to 3500 RPM. While under this condition the engine will only run up to about 4000-4100 RPM at WOT. Normal WOT is about 5200 RPM. Here's a strange phenomena I've just recently noted ! If I only advance throttle's to 3200 RPM, I can cruise seemingly all day without a glitch. I never get into the tach flicker or lose power at all. I can throttle to WOT from 3200 and get full RPM.
Here's what I've tested so far. Fuel pressure under way remains +/- 2 lb @ 33 lbs measured from the front of the engine. I experienced a VST screen problem early on with these VST engines but that problem was solved long ago with the addition of RACOR filters after the standard Merc water seperator fuel filters. Plugs and plug wires have been replaced. Distributor cap replaced. Computer hookup seems relatively useless to find this problem as far as I've been told.
I have Gaffrig tachs that were installed when the engines were built. Is it possible that a problem with a tach cause a problem of this sort ? After all, the ignition goes directly to the tach. I will be swapping the tach positives this weekend to see if the problem moves with the tach. I'm not very optimistic of this being the problem but am hopeful.
Anyone ever heard of a tach causing an engine problem of this or any other type ? With the tach flicker, it seems an electrical problem. Does anyone agree with that ? I'm getting very weary of this problem that no one seems to be able to pin point.
Help ! Please !
Last edited by deboatmon; 07-28-2005 at 03:39 PM.
07-29-2005, 10:03 AM
#3
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Re: Tachometer and ignition problem ?
Originally Posted by deboatmon
Computer hookup seems relatively useless to find this problem as far as I've been told.
Dave
