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Tips to diagnose and fix excessive spark knock (ping)

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LastDeadLast

Tips to diagnose and fix excessive spark knock (ping)

All,

1985 5.0 EFI automatic with 96K miles.

I'm having a problem where I'm experiencing spark knock when the engine is under load and low RPM. It appears to happen more when fully warmed up.

What I have done:

1. Replaced EGR valve, EGR position sensor and knock sensor
2. Fuel pressure at idle is 40psi and 45psi with the vacuum line disconnected. As part of other issues, I've replaced both tanks, all three fuel pumps and fuel filter
3. KOEO and KOER no errors
4. Checked timing during KOER and verified that timing is being controlled correctly
5. I was told by the PO that the injectors are new (they look new)
6. 15psi of vacuum at idle
7. New plugs and wires

Does anyone have any suggestions for next steps?

Thanks,
-Shannon

1985 F150 XLT
1965 Mustang Convertible
2013 F150 Platinum

Gary Lewis

Re: Tips to diagnose and fix excessive spark knock (ping)

Administrator

You didn't say that you pulled the SPOUT connector and verified that the initial timing is where it is supposed to be. The fact that the computer is controlling the timing is good, but it doesn't know where you have the initial timing set, so if you have it advanced over stock then you may well get spark knock under those conditions.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

LastDeadLast

Re: Tips to diagnose and fix excessive spark knock (ping)

Sorry Gary, I should have mentioned that. I set the initial timing at 10 degrees with the spout disconnected.

The KOER test put the timing right at 30 degrees, so I think the ECU is timing the engine right.

-Shannon

1985 F150 XLT
1965 Mustang Convertible
2013 F150 Platinum

Gary Lewis

Re: Tips to diagnose and fix excessive spark knock (ping)

Administrator

The ECU assumes you put the initial timing at the specs, and has no way to know if you do or not.

It is possible that your harmonic balancer has slipped and your 10 BTDC is more like 12 or 14. I've had two balancers on these trucks that had slipped. So I'd use a piston stop to determine if the balancer's marks are correct or not.

But if the balancer is correct and you have it timed to the spec then all I can think is that you have carbon buildup or the plugs are too hot.

Gary, AKA "Gary fellow": Profile

LastDeadLast

Re: Tips to diagnose and fix excessive spark knock (ping)

Thanks Gary,

I'll verify the balancer and go from there.

-Shannon

1985 F150 XLT
1965 Mustang Convertible
2013 F150 Platinum

ArdWrknTrk

Re: Tips to diagnose and fix excessive spark knock (ping)

Administrator

In reply to this post by LastDeadLast

Doesn't this truck have a knock sensor on the driver's side lower intake?

It seems Vinny was looking for one five years ago... https://www.ford-trucks.com/forums/1477220-knock-sensor-part-number-1985-f150-5-0l-mfi-eec-iv.html

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Tips to diagnose and fix excessive spark knock (ping)

Administrator

Yep, Vinny was looking for one and seemed to have a hard time finding one. But Shannon said he replaced his.

So at first blush you'd think the ECU would back the timing off to prevent knock. However it can't back it off more than the initial timing, so if the initial timing is too far advanced it'll ping/knock.

Or if the knock sensor is bad... From whence did it come? My nephew won't install a part that was sourced from Rock Auto since way too many of them he got were bad.

Gary, AKA "Gary fellow": Profile

LastDeadLast

Re: Tips to diagnose and fix excessive spark knock (ping)

I searched all over the place for a knock sensor. I finally found a NOS Niehoff sensor part number FF1000, that was able to cross reference.

The truck ran no different after I replaced the sensor, but I no longer got a code.

-Shannon

1985 F150 XLT
1965 Mustang Convertible
2013 F150 Platinum

LastDeadLast

Re: Tips to diagnose and fix excessive spark knock (ping)

So I purchased a fuel rail from a 1986+ EFI truck awhile back with the intention of installing it mainly because of the better design and the Schrader valve for diagnosing fuel pressure. I finally got around to installing it today.

I also installed some new Ford 19lbs fuel injectors that I had for my old Mustang when it was stock. The injectors that came with the truck were "new" but they looked to be the cheapest that could be sourced in order to sell the truck.

I discovered that the EGR tube connecting to the intake was loose: Definitely not air tight. I also replaced the O2 sensor.. what a PITA that was.

Normally I don't like to change so much when I'm diagnosing a problem, but taking the intake off is a pain, so I just did it.

Anyway, with all the above, it's no longer spark-knocking; And it feels like it gained 10-20 hp!

-Shannon

1985 F150 XLT
1965 Mustang Convertible
2013 F150 Platinum

Gary Lewis

Re: Tips to diagnose and fix excessive spark knock (ping)

Administrator

Excellent! Glad you got the problem solved, regardless of how many parts you put on it.

Gary, AKA "Gary fellow": Profile