Knock sensor; Where? 1991 PCM 5.8 ProTec
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=1934
Printed Date: November-26-2024 at 7:42am
Topic: Knock sensor; Where? 1991 PCM 5.8 ProTec
Posted By: Guests
Subject: Knock sensor; Where? 1991 PCM 5.8 ProTec
Date Posted: June-25-2005 at 11:59am
Can someone tell me how to identify the knock sensor on a 1991 PCM 5.8 w/ProTec ignition? (not the H.O. version) I need to verify/adjust the timing later today and I understand the knock sensor needs to be disabled to set the idle timing.
Thanks, also is an engine wiring diagram available online?
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Replies:
Posted By: David F
Date Posted: June-27-2005 at 2:29pm
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The knock sensor is located on the rear of the port cylinder. It will have a two wire connector attached and be the only sensor type device.
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Posted By: Guests
Date Posted: June-28-2005 at 10:41am
Thanks David! Whew... Tons of views and only one reply this week. Thank you. Now I gotta go set the timing again because I unplugged a few other sensors to time it but not that one...
Carb's being rebuilt as we speak (by a pro, I gave up) and I'm considering the "ProTec replacement kit" from SkiDIM. Any experience with that job?
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Posted By: David F
Date Posted: June-28-2005 at 1:11pm
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Why do you want to get rid of ProTec?
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Posted By: Guests
Date Posted: June-28-2005 at 9:40pm
David F asked me, "Why do you want to get rid of ProTec?"
David,
This is a 1991 Natique Excel 5.8PCM w/ProTec electronic ignition, Holley 4160 carb, and not the H.O. version. For several years it will be running along 14 to 20mph and suddenly rapidly backfire through the carb until the engine dies. It will not immediately restart, but if you reset the ignition breaker and wait a few minutes, it will restart and run like nuthin' happened for anywhere from 2 minutes to 2 days before the same thing happens again.
FRUSTRATING, and I've heard PCM had alot of trouble with the coil pack & modules on that system.
I would be glad to keep it stock if the backfiring problem goes away.
PS: Carb is off being rebuilt now; will reinstall and test in a couple days. According to Holley specs, it's a 4160 List No. 50469-1 which should have had a #25 power valve, but I found a #85 in the carb. Current replacement carbs have a #65 power valve.
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Posted By: David F
Date Posted: June-29-2005 at 12:40pm
Well, that sure does sound like a temp related ProTec problem. Seems that the timing is going haywire when it backfires. Let the faulty part cool and back to normal. Hence the problem is probably in the control module because if it were a coil pack, I would think the engine would just miss badly or die out without backfiring. Are the parts NLA? I recently purchased a boat with ProTec and TBI that I have not had a chance to run yet...hope I do not have problems.
I think you want the #65 power valve in your carb.
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Posted By: Guests
Date Posted: June-29-2005 at 10:03pm
David F: described it exactly... Control module pukes and starts firing one coil all the time instead of four coils alternately. "Pop, pop, pop" goes the carb and the boat drops back into the water with the engine dead... Starts back up in a minute and runs fine.
It would seem that the coils & module would get hotter (heat soaked) after shutting down than when running since there's nothing carrying away the heat after you shut the engine off?
ANYWAY... Got the Holley back today and will test drive the boat tonite. It had a #85 power valve in it and I've changed to a #65 with the rebuild (1st rebuild in 14yrs)
Wish me luck!
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Posted By: Jim_In_Houston
Date Posted: June-29-2005 at 10:05pm
Tom, I'm real happy with the 85 power valve in my 289. Let me know if you can detect improved performance with the change.
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Happy owner of a '66 and a '68 Mustang
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Posted By: Guests
Date Posted: July-02-2005 at 10:16am
"Jim_in_Houston" posted: <<Tom, I'm real happy with the 85 power valve in my 289. Let me know if you can detect improved performance with the change.>>
Ok, I got the Holley 4160 (List No. 50469-1) back and installed on the 1991 PCM 351 Ford yesterday: Starts and idle are PERFECT! I unplugged the knock sensor and set the timing to 26 BTDC @ 600rpm. No adjustment was necessary. I plugged the knock sensor back in and checked timing again, but there was no difference: COULD MY KNOCK SENSOR BE BROKEN?
Acceleration was slightly 'boggy' but it's a Nautique Excel and not a rocketship, anyway it was everything it ever was when new, so that's good. Fully warmed up, I ran some more holeshots to top end and on the third run, the motor bogged down and I'm pretty sure the ProTec system went into limp mode: 2500RPM is max, even if you use 'throttle only' in neutral and go wide open... 2500 loping, bucking rpm is max. I shut it off and reset the ignition breaker and it immediately restarted and ran just fine for one more run, on the second run it again went into limp mode.
Good news: No more carb backfires
Bad news: Still going into limp mode.
I will try rewiring the ignition breaker, voltmeter, and adding a heavier guage ground wire to the ProTec engine ground today. I'll follow the advice posted a few days ago about the 1992 PCM/ProTec going into limp mode. Also, I will disconnect the ProTec ignition module plugs, clean them, and reinstall with terminal grease
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Posted By: David F
Date Posted: July-05-2005 at 5:10pm
Tom:
The reason for disconnecting the knock sensor is to prevent Pro Tec from going into "cruise" mode. "Cruise" mode changes the ignition timing slightly for improved fuel economy. "Cruise mode is activated only when the control module senses that the throttle has remained stationary for at least 30 seconds. "Cruise" mode is active even at idle. So, to prevent a false static timing reading, you disconnect the knock sensor which prevents Pro Tec from activating "cruise" mode. Thereby, upon reconnecting the knock sensor, you would not necessarily see a timing change unless you do not touch the throttle for 30 seconds or more. Even then, I do not know how much the timing is changed when in "cruise" mode.
There only two things that activate "limp" mode: 1) low oil pressure (or faulty sensor switch) and 2) high engine temperature (or faulty sensor switch). I would disconnect both of these switches and testing before doing anything else. I believe the sensor send ProTec into limp mode by completing a circuit to ground. So disconnecting the switches will prevent the circuits from being completed to ground. If I have this backwards, a bad ground at the switch (via the threads of the switch) could be your problem. If so, ground the sensor wire directly and test. Are you getting a red engine warning light? If not, then check the light. And then finally, I suppose is could be a faulty circuit to one or both of the sensor switches...or even within the control module.
Good luck.
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