Ford 302 EFI Engine Issue at higher revs only

I have a 302 Ford (Australian motor from an XR8 AUIII Falcon) in my RCR40 which has an issue that occurs only when revs rise above 4000 (approx). This occurs every time, and beyond 4000 rpm the acceleration drops off dramatically and revs rise very slowly.

I have a fuel pressure gauge in the line and have confirmed that the fuel pressure stays consistent at 39-40 psi, below and above 4000 rpm under load. I also connected a friends air/fuel mixture gauge expecting a lean out condition, however this did not occur and mixture looked OK, a bit rich at lower RPM.

Other things I have performed are;

Cleaned MAF
Checked correct operation of throttle Pos sensor
New Spark Plugs
New Leads
Checked Injector resistance is consistent across all injectors
Checked Compression was consistent across all cylinders

Engine is unmodified and came from a wreck. ECU was provided with engine and has a J3 daughter board connected to remove unwanted inputs like auto trans, immobilisers and other irrelevant things.

Any thoughts or suggested further tests to help diagnose?

Thanks
Colin
 
Colin,
I'd start thinking of the spark timing aspects. What's the timing at idle? How much timing advance is added as rpm increases. What's the total timing and when does it go "all in"?
 

Ian Anderson

Lifetime Supporter
Wrong rotor arm fitted?

Some have a forward edge, some straight and some trailing edge.
With wrong one the spark will be firing when it is not exactly pointing at contact point for plug.

Just a thought

Ian
 
Wrong rotor arm fitted?

Some have a forward edge, some straight and some trailing edge.
With wrong one the spark will be firing when it is not exactly pointing at contact point for plug.

Just a thought

Ian

Good call Ian , it could well be spark scatter. Try a timing light on #1 and see how it behaves as the revs increase.

Bob
 
Colin,
I experienced the very thing you have. Mine was with the FAST ECU. They are different but I think if you investigate your software you may find what we found. What you are seeing (and experiencing) is a change in the timing at the 4K threshold(retard). You won't see it except on the dyno. We had to dig well into the software to find it. Once we removed the retard, the engine sang like a bird. Take a look at my post and the dyno results to see what I am talking about.
For what the others are talking about(spark scatter etc.), you need to phase your distributor. There are several ways this is accomplished. I chose the way it is demonstrated onn the MSD Utube site. You also can search for other videos on timing, crank triggers etc.
https://www.youtube.com/watch?v=aWMlNwGW0tM
For what we did you can see my posting here:
http://www.gt40s.com/forum/video-pictures-buffet/48745-dyno-day-drb-5-a.html

Bill
 
Guys, many thanks for the replies. Based on your comments I will chase a timing issue, as pointed out by all, does seem to fit the symptoms.

Sounds like I need to get the car on a dyno as I suspect timing is OK with no load (as I can rev it at idle easily to the 6500 rpm limit) however may be being retarded or not advanced correctly under load.

I will post what I find.

Thanks again to all who responded.

Regards
Colin
 

PeteB

GT40s Supporter
Check your wiring. I had a very similar issue with my Cobra when I accidently connected the "start" wire from the computer to the ignition terminal, rather than the start terminal on the ignition switch. This wire pulls timing when the engine is cranking. Long shot, but it could be your problem.
 
From further research it looks like the issue may be due to the Factory Ford ECU not getting the speed sensor input (VSS) and protecting the engine with a limp home mode or timing restriction of some sort. I have a GPS Speedo and thought no speed sensor was necessary.

So now the question is how anyone with a similar setup of Ford XR8 engine with factory computer and any transaxle got around this issue. The 302 XR8 engine with factory ECU must be a common configuration for the DRB or other Australian replicas as it is a known configuration to pass ADR's.

Anyone with a similar setup able to help?

Thanks
Colin
 
From further research it looks like the issue may be due to the Factory Ford ECU not getting the speed sensor input (VSS) and protecting the engine with a limp home mode or timing restriction of some sort.

Colin, I think you are onto it. Different car but my EB2 falcon would not rev past a hard ignition cut at fairly low rpm with the plug to the VSS removed from the gearbox. If you don't have a VSS signal could you send the ECU a tach drive output or something like that. All it probably needs is a square wave of some description.

Cheers, Andrew
 
Thanks guys, great advice.

Martin, do you know if your Porsche speed sensor is connected directly to the Ford ECU VSS line?
As Andrew mentions in his post, a square wave input is required into the Ford ECU and I am unsure whether a mechanical type speed sensor will produce the correct signal or if some circuitry is required to convert the signal to a square wave. The wiring diagram for the original car (Falcon XR8) showed the speed sensor went to dash electronics before passing through to the ECU.

On the completely weird side, when I checked the plug into the ECU, there was no wire into pin (58) for the VSS signal. I checked it a few times thinking I had lost the plot, however are convinced its been removed, by verifying other wiring pins and colours to ensure I was looking at the right pin. (probably by the guy I paid to modify the loom a few years back)

Thanks again, this is the last issue I have with the running gear, and its becoming a tough one to resolve.

Regards
Colin
 
I Have my speedo and that wire connecting to it,we had a scan tool on it and it didn,t raise any faults,I think the chip I put in the ecu also to allow me to run with out the body modal may also helped,realy works well idle and drives great.
 
a hall effect sensor will give you a square wave.
You may need to have the same amount of counts as the original, unless you can change it in the software.

Jim
 
Colin,
I went thru a similar situation.
Ford transmission produce a Sinewave of 8 pulses per revolution (ppr) for the ECU VSS.
The transmission you have will probably put out more ppr than the ECU want to see.
My transmission put out 40 ppr.
I had to use a Dakota Digital SDI-5E to lower the transmission ppr to what the ECU needed.
It fixed my VSS issues.
No more CEL light, no more ECM P0500 codes, no more OBDII monitor test issues, no more RPM issues.
Hope this helps you.

[URL="http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/prd126.htm]Dakota Digital[/URL]

[URL="http://www.dakotadigital.com/pdf/650528a_SGI-5E.pdf]Dakota Digital Manual[/URL]
 
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