1992 5.0L Ford RPM shudder and Trim RPM drop

[Offrddrver]

[FONT=&quot]ISSUE: Motor RPM shudders lightly on holeshot - no skier. [/FONT]​

[FONT=&quot]Motor shudders horribly on holeshot - with skier or wakeboarder (even light kids). [/FONT]​

[FONT=&quot]Once on plane (no skier) the motor RPM climbs at a steady pace, but only reaches around 3600 RPM, and just sounds wrong like its bogging down. I can just let the motor run like this for a couple minutes, and then it will just jump instantly up to the 4400 RPM+ range, which is the normal W.O.T. for my motor. [/FONT]​

[FONT=&quot]When motor sounds wrong at 3600 rpm the speed is around 35MPH. [/FONT]​

[FONT=&quot]When motor jumps up to the normal W.O.T. at 4400 RPM + the boat runs 42 MPH (this is top speed with my "POWER PROP"/SKI PROP) This is normal when the boat was running GOOD. [/FONT]​

[FONT=&quot]Next issue that appears to be related to this; when running at W.O.T. and trimming up/down the motor shudders until the trim button is released. [/FONT]​

[FONT=&quot]I believe this to be an electrical issue, but I have done some basic fuel checks also. [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]OTHER NOTES: Boat starts on first key turn EVERY time. Boat never dies even when it sounds wrong. Boat idle is set at 620 RPM with external Tach/Dwell meter. Idles smooth on muffs or in lake. Ignition timing is set at 10 degree BTDC. Timing advance can be seen with timing light when lightly revving the motor on muffs, or when at the lake. Motor never shudders when testing on the muffs (however, it is NEVER run W.O.T. on muffs). ESA interrupter switch IS NOT the issue as it has been monitored for proper move and switch continuity. ESA Interrupt Switch has also been removed and motor/RPM shudder is still present. Pressing the switch with my finger causes a large pulsing in motor (correct). [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]CHECKS/REPAIRS: All old gas ran out, and fresh gas with seafoam and stabil added on next two tanks. (always run stabil every tank) Gas filter pulled and dumped in clear container (no water, no separation). Carb cleaned, rebuilt and idle reset at 620 RPM with external tach while warm, in gear(no extra throttle applied), on the lake. Spark plugs pulled and are very clean, plug gap is set to spec (.035). Gap on Prestolite IBD distributor sensor to sensor wheel set at 0.008 inch. Ignition timing and advance checked every time adjustments are made, no issues. Battery is always kept at full charge with trickle charger, and new battery installed recently. All ground and positive wires are clean and tight. Found and repaired a worn wire in the throttle to the trim switch, but this did NOT fix the RPM shudder when the trim button is pressed.
[/FONT]​

[FONT=&quot]Current test: SELOC OMC STERN DRIVES 1986-98 repair manual and Clymer repair manual instructions being followed. Seloc section 10, 45 - 49 followed for Prestolite Integral Breakerless Inductive Distributor (BID) system. [/FONT]​

[FONT=&quot]Primary Voltage test: Battery 12.46Vdc, POS+ Coil to GRND = 8.51 Vdc (Low Voltage), Voltage Drop Test POS+ Battery to POS+ Coil is >1Vdc (pass), NEG- Battery to Prestolite sensor body is <1Vdc (pass), NEG- Battery to NEG- Coil = 1.68 Vdc, Due to <4Vdc then remove neg wire from coil and read NEG- Battery to NEG- Coil = 12.4Vdc (possible sensor shorted out), NEG- Battery to Neg- Coil (neg wire attached again) with screwdriver at face of sensor = 12.36 Vdc (good). Then it says if initial reading was greater than 8 Vdc (mine was 8.51 Vdc) then shorted primary coil or floating ground on distributor. Distributor is clearly grounded. Removed coil and have the following: POS+ to NEG- = 1.9 Ohms, NEG- To High Tension = 11.26 k Ohms, and POS+ to High Tension = 11.26 k Ohms. [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]Sorry so long, but does anyone see an issue with the above distributor test results that stands out as the cause of the main issue? [/FONT]​

[FONT=&quot]If I had any issue with the above tests would the boat even RUN? [/FONT]​

[FONT=&quot]Or are the above tests meant to check only if the boat won't even RUN? [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]Last item noted: If I have the Prestolite sensor REMOVED out of the distributor body I get 12.36 Vdc from the sensor body to battery ground if the KEY position is ON. If key is OFF I get 0 Vdc. [/FONT]​

[FONT=&quot]Is this a valid even a valid test? [/FONT]​

[FONT=&quot]If this is a valid test, then I have to believe the sensor is shorted internally based on this test and the BOLD letter item noted above.....Do you agree? [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]Thanks for any help, and I hope this may help someone else as I see similar posts to my issue, but have never seen someone say what the actual fix was. [/FONT]​

 

[Bondo]

[FONT=&quot]Next issue that appears to be related to this; when running at W.O.T. and trimming up/down the motor shudders until the trim button is released.[/FONT]​

[FONT=&quot]I believe this to be an electrical issue, [/FONT]

Ayuh,..... Welcome Aboard,...... Clean the Grounds, startin' at the battery posts, to shiny clean metal, 'n reassemble, tighten, 'n grease em' to keep 'em corrosion free,....

If yer terminals got wingnuts on 'em, Toss 'em, 'n get real nuts, use a wrench to tighten, insteada old pliers,...

 

[Offrddrver]

Thanks, the boat is sitting right now in pieces, but hope to take it out next week.

 

[Offrddrver]

No Title

Based on two items I've upgraded my Prestolite IBD sensor (and coil) assembly over to a Pertronix Ignitor II and Flamethrower II distributor sensor and coil.
1. Per the Seloc Maintenance manual troubleshooting of the IBD showed a possible internal sensor short.
2. After further troubleshooting after finding 1 I found that removing the Prestolite IBD sensor and applying meter leads from battery NEG to senor meta body showed over 12 VDC. When installing the sensor into the distributor body it sparked. (again showing an internal short to POS+)

All is installed and ready for MUFF test in the morning.
If MUFF test is good, then lake test.

 

[Offrddrver]

Already note the above change shows a 12.46 Vdc from battery ground to coil POS+ (original sensor showed 8.51Vdc)
Voltage drops to 11.74 Vdc when trim is run
(motor is not running during these initial tests)

More results Saturday.

 

[Offrddrver]

PROBLEM SOLVED: The troubleshooting noted above was the resolution.
New Pertronix Ignitor II and FlamethrowerII coil installed.
1. Holeshot without skier - Great
2. Holeshot with skier/wake-boarder - Great (slalom skier 260 lbs and wake boarders up immediately)
3. RPMs great through the whole range.
4. No signs of RPM drop with this new system.
5. Shifting is even better now then with my original Prestolite setup.

6. One minor negative is that I lost about 2 mph at W.O.T. trimmed up. 40mph with power prop
Possible fix - I still have to adjust my plug gap (add 0.005) as noted by Pertronix manuals (I just didn't have time before today, but will adjust before next run out.)

Notes about the Pertronix Ignitor II and Flamethrower II install:

1. I had to adjust the timing back to 10 deg BTDC after install.
2. Advance checked and looks good and stable increase as throttle increased.
3. Voltage at the coil Pos+ is a clean 12.46 Vdc
4. Will have to pull plugs and open by .005 (so 0.040 for my setup)

I hope this helps someone else in the future.

Best regards,

Offrddrver
(Off Road Driver)

 

[Offrddrver]

Final setup complete.
Added the .005 gap to the plugs.
And minor tweek to the distributor rotation.
Boat is back to 42 mph W.O.T. trimmed up.

This one is considered closed.