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Discussion Starter · #1 ·
Hi,
I have recently started a newly built 351 Windsor i have in my 1966 Mustang.

I Have a problem with an unstable idle, partially cured by installing an idle air adjustment plate. Second issue is i have a spark knock under medium to full throttle.

Here's my engine specifics;
1989 351W with a Ford E303 Roller cam, Scat 393 Stroker crankshaft, Edelbrock heads 2.02 intake and 1.6Exhaust
Trickflow intake manifold
70mm BBK throttle body and EGR plate
77mm Pro-M Mass Air Flow Calibrated for 36# injectors
MSD TFI distributor and hi power coil. (Crane HI-6S self destructed)
Compression 10.4:1
Running 96/98 Ron Fuel which is available off the pump here

I have duplicate parts for all the main EFI components and have swapped these in without any evident improvement. Currently runs a steady 13in of vacuum at idle - not sure if this is appropriate for the cam which I understand is fairly mild for this capacity engine.

Anyone have any suggestions to help with these problems? Let me know if you need more information.

Greatly appreciated,
Guy
 

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My first question would be, have you checked the timing?
 

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I would then look for vacuum leaks.
 

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Discussion Starter · #4 ·
thanks for the responses--timing at only 6degrees and no leaks that i can find with the vacuum .
any idea what vacuum should be with the e303 cam?
 

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Should be quite a bit, it isn't that radical. I'd say 15-18 inches.

Spark knock can be caused by a few things...
1. Timing
2. Cooling system... overheating
3. Base engine... oil level low, low compression in one or multiple cylinders, leaking intake manifold gasket
4. Fuel/throttle body... filter, pump, lines, regulator, sender filter, injectors
5. PCV
6. EGR
7. Air intake system
8. Thermactor system
 

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thanks for the responses--timing at only 6degrees and no leaks that i can find with the vacuum .
any idea what vacuum should be with the e303 cam?
i think you should be able to run more timing than 6 with 98 octane. even with 10.5:1 compression. up the timing and your vacuum reading will increase. 13 is kinda low, really low. E303 cams are smog legal in California, so Im thinking you should be reading at least 17-20 in Hg. Does your condition worsen when you up the timing?
 

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Wow thats a really small cam for that setup. Maybe your off a tooth On your distributor gear
 

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Discussion Starter · #8 ·
THanks guys responses are helpful - must say that i have been through pretty much all of the standard areas to look at as I have a copy of "Ford Fuel Injection" By Probst which covers these areas.

Two interesting threads i have found on this site cover setting the fuel pressure which i only now understand is to be done with the vacuum disconnected and issues with BBK throttle body whistling noises. Recommend these threads to anybody with the same concerns.

Have managed to resolve to some degree the idle with the correct fuel pressure and other usual adjustments including Ford setting procedure.

Remaining problem is pinging under WOT and suspect that this is due to lean fuel - my son is setting up an M20 BMW turbo and we have ordered an Innovate Lm-1 Air/Fuel Wideband meter which will help diagnose whether or not we are running lean.

EagleAutosports i rang ford Racing Tech advice line and they advised that vacuum reading of 13in is normal. he has also suggested i take some readings at MAF terminal D at RPM to see whether the signal to the ECU is within specification. HAve to get back to him on this one.

Point raised by lxarlo, Yes you are right 6 degrees is conservative, though this is intentional until we sort the knocking problem - have since found out that our 96/98 octane is in RON rating which is only comparable to your 92/93 octane. This advice received from Ford racing tech. Apparently your fuel is assessed on a different basis.

I will be away for a week or two enjoying some Golf so i will check in when i return.

Thanks for the replies and suggestions. :bigthumbsup
 
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