Intermittent “Lean Spikes” on Air/Fuel Ratio Gauge...

[slotcarone]

Check all of the rubber hoses between the tank and fuel pump. Any one of them could be collapsing or sucking air bur not leaking.

[Grant]

Rocky.
Probably not something you want to hear, or you may have read it already on another thread in the past.. but I had a strange issue on our convertible years ago, the same sort of thing .. died and then went again etc, my tests also showed it was a fuel problem and I could never suss it,.. when I stripped the engine to do away with all that Yank Emission Rubbish that you lot made us have to have I noticed the lobe on the camshaft that pushes the fuel pump rod was worn badly, I changed the cam to a Magnum one anyway and it was all good after that problem solved, I was shocked that the lobe was so badly worn, but there really is heavy pressure needed to push that mechanical fuel pump.. having said that, I have never heard of anyone else having this problem with an Interceptor

[RockyUSA]

Hi Grant -

I saw some of that on the "For A-Bodies Only" Mopar thread - if that's the case, I'll put an electric fuel pump back in until I rebuild this motor.

Anyway - I'll keep trying to get to the root of the problem, one step at a time.

Thanks -

Rocky

[RockyUSA]

I wish I could post up a file of 40 Mbytes for about 15 seconds of iPhone video.

I got my fuel pressure gauge installed by the carb. At idle - solid 6 psi.

When accelerating, the fuel pressure falls down to almost 0... Amazing how fast it falls off.

So it's either the fuel pump pushrod, or (more likely) the $45 M165187 Mechanical Fuel pump. On my Pantera, when we ran the engine on the dyno, I have seen these "low cost" pumps do this exact same thing... run fine at idle, and then as the RPMs go up, fuel pressure falls off.

Anyway - I am happy to report I have solid data to go on.... but there are many more steps needed until I close the book on this.

Rocky

#1 - Initial reading (just off idle)

Initial Reading - Off Idle.JPG (37.26 KiB) Viewed 5098 times

Acceleration - Fluid Forced to back of gauge

Acceleration - Note Fluid building in the back of the gauge.JPG (36.98 KiB) Viewed 5098 times

2 Seconds later...

2 Seconds later.JPG (32.03 KiB) Viewed 5098 times

End of Run

End of Run.JPG (34.74 KiB) Viewed 5098 times

[Steve Payne]

The easiest option would be to fit an electric fuel pump.

Many Interceptors have electric pumps to get over poor starting.

Steve

[RockyUSA]

That's too easy, though!

I have a plan for a "auxiliary" electric fuel pump for carb priming. I really prefer the mechanical pumps, and figure this is a good, smaller project before I tear more seriously into this engine.

Rocky

[RockyUSA]

I am following this thread relentlessly... I can't get enough of it.

So I pulled off the fuel pump, and also removed the fuel pump pushrod.

I found the pushrod seems short (worn). The end agaist the cam is shorter than the other.


Length
Should be: 3.220"
Measured: 3.046"

It's .174" too short!


Anyway, I think I am going to order a new rod and pump from Mancini Racing...

https://www.manciniracing.com/cabheen5psis.html" onclick="window.open(this.href);return false;

Should I get the hollow, carbon fiber racing fuel pump pushrod (Comp Cams) for $29 or the $14 steel rod. I am sure I need the steel tip version (for flat tappet cams) vs. the bronze tip for roller cams...

https://www.manciniracing.com/search-re ... pump%20rod" onclick="window.open(this.href);return false;

[slotcarone]

Rocky you need a stock replacement push rod designed to last a long time not one designed for racing. I would try this before putting an electric pump on.

[RockyUSA]

I know that. It was a little joke.

It is actually pretty hard for me to believe that a fuel pump pushrod for "racing" can do anything different than the stock pushrod of the correct dimensions, but I guess they are in demand, or they wouldn't be making and selling them.

[slotcarone]

Rocky some people just have to have all the goodies like the Carbon fiber pushrod and of course yellow spark plug wires! I have always found that the longer the list of goodies in the engine compartment the worse it runs!

[Dion]

I have a plan for a "auxiliary" electric fuel pump for carb priming.

How would you plumb this in? Between tank and mech pump or between mech pump and carb? In series or parallel? Can you run both pumps at the same time? Or would something be needed to switch off the elec pump after starting?

The easiest option would be to fit an electric fuel pump.

Is this also the best option? Do do away with the original mech pump, fit a plate instead and an electric pump. What type of electric pump - I would guess a low pressure pump? Any suggestions?

[RockyUSA]

RockyUSA wrote:

I have a plan for a "auxiliary" electric fuel pump for carb priming.

How would you plumb this in? Between tank and mech pump or between mech pump and carb? In series or parallel? Can you run both pumps at the same time? Or would something be needed to switch off the elec pump after starting?

So my plan was to put the fuel pump in parallel with a one-way check valve on the hard-line that I am working to install. So the electric fuel pump will pressure through the mechanical fuel pump - they (typically) also have a check valve system that lets pressurized fuel flow through.

The goal is to hit a switch to pump fuel to the bowls for a few 10s of seconds, once those are set up, then the electric pump is disabled (and out of the fuel circuit). Then the mechanical pump takes over.

Some of this needs some thought, but I am pretty confident it will work.

The hard part to implement is the fuel check valve, and getting the right fittings...

Rocky

[Steve Payne]

Rocky
You could have it automatic, power the pump from the oil pressure warning light via a relay so as soon as you switch the ignition on the pump would run and it would go off when the engine started.

I would also suggest if you do it this way you have a crash switch in the circuit.

As far as a pump I use Fuel Flow pumps https://www.ebay.co.uk/itm/FuelFlow-020 ... 1192454236" onclick="window.open(this.href);return false;
They are almost silent and work well, some pumps I have bought in the past are very noisy even with insulation and some don't last more than a few months. The problem is the market is saturated with Chinese pumps and some are just relabelled I presume.

Once you have an electric pump you will wonder why you put up with a mechanical pump, switch the ignition on even if you have not used the car for several months, wait a couple of seconds and hit the key. No more cranking hot or cold to pump fuel through.

Steve

[RockyUSA]

Thanks for the advice, Steve -

I look into the fuel pump you recommended.

I have had a lot of trouble with cheap fuel pumps on several cars.

Regards -

Rocky

[RockyUSA]

Difference between a 65,000 and new fuel pump pushrod...

It's hard to believe!

IMG_0491_Oil_Pump_Pushrod - Cropped.JPG (43.63 KiB) Viewed 4989 times