Low Fuel Pressure at WOT

DAMN!!!!!!

I bought mine back in 2016 to have on the shelf, and I bought a complete HFCM a few years back.

I felt bad a little while ago when I destroyed the two pumps for the video. Now I really wish I never did.

My pump order from Diesel Filters.



The full HFCM (Carter)





This is a complicated pump, so some of the aftermarket companies that would private label from Racor may not have changed their pricing as yet. I may order one to see if it is the same part, as best I can tell.

Back then, I bought 2 HFCMs to compare, one Carter (NAPA) and a Delphi. Both were actual Racors. Carter is part of Federal-Mogul.

Both had this situation; Racor tried to obliterate the Ford logo on the bracket rather than stamping a new bracket.

And part numbers that are on the cap of a Racor pump.

I sent one of the HFCMs back to RockAuto. I also bought several years of FoMoCo main battery cables when they were in the $80 range to take measurements. I sent them all back; last I saw, they were selling for a few hundred at dealers.

It's looking like parts do better than some stocks.

I've got '66 GT-350 parts like that. But the reality is you can still do better with stocks.

Back to the subject. I just ordered an Airtex pump from RockAuto, so I will let everyone know if that is a Racor when I get it. Airtex is an OE water pump manufacturer, but I know they private label parts for their aftermarket sales.

The Airtex pumps were not, nor ever have been, in the cheap China parts cost range. Hopefully, they haven't caught on yet. Used a RockAuto discount code. RockAuto lets you use their cheap shipping if you send it back.

XDP has it for a little less than RiffRaff.



And they show the Dorman one at the old price of the Racor. I know nothing about where this comes from.



The Airtex on Amazon sourced from Autoplicity in the ad shows the Racor part number on the cap.

I would define a regulated input as a closed system with no fuel return, such as we use with a compressed air circuit. Pi**ing points.

A long time ago, ~2002 with the 7.3L, I put one of our test data acquisition computers in my 7.3L to measure the fuel pressure at the back of the 7.3L with the stock system and a "regulated return". From that data, there was no pressure drop at the back of the heads with the stock system compared to the front of the heads, and there was more pressure variation in the head's fuel rails with a flow-through system. Discussing that with an engineer who worked on diesel fuel systems; his explanation was diesel fuel entrained air release due to the turbulence in the rails and the spit-back from the injectors as the plunger was moving and before the check valve closed. It seemed to be a reasonable explanation. But whatever the cause, there was more variation in the fuel rail. The test was done with one head left stock and the other with the return flow setup, so there was no variation due to operating conditions, temperature, or demand.

I'm not inclined to do that.

No matter the system, volume input is always important, I agree.

I agree about the banjo bolts, too. That was part of my past discussion about the fuel pulsing, they were there to isolate, and the flow rate was high.

I was doing the testing when the 7.3L 'cackle' was the subject. Some stated the flow-through was the cure. Unfortunately, I lost most of the data when my test facility was closed in '08; it was all done at work. But I found some here at home on my old laptop afterward.

It was at idle, comparing the passenger bank with the stock condition and the driver's bank flowing through with a regulated return. There is always spiking in the rails due to the injector spit-back, but it's more pronounced and more negative with the regulated return. I also tried to isolate if it was one injector and tried both hot and cold conditions. Injector 2 seemed to be the most problematic for the negative pulse, but the overall Delta in pressure still prevailed with the regulated return. Flow and pulsing can release the entrained air out of the fuel, and the goofy thing with the 7.3 is that the fuel rails were under the injector ports, so the cavity to fill the injectors was above. So any released air would rise, and if you pull the injectors after 500-1000 miles, you will see a bathtub ring showing trapped air in the chamber. Sometimes, the injectors would not fill entirely with fuel, and some air could get pulled in.

The remaining data.

Updates... Some good, some expensive.

After reading the replies about the pumps, I decided to try one of the airtex pumps from Amazon, to see if it was actually a Racor, figuring worst-case I return it. It was not a Racor, even though the picture in the listing showed the Racor part number. It had no markings on it at all. I tried it out, and deadheaded it would build well over 100psi, pegging my gauge, but boy did it make noise. Even when I hooked it up in the truck, it made a terrible racket. Regulated pressure was in the low 60s, but I noticed that if I left the key off for a bit and let the pressure bleed down, then turned it back on, it would take several seconds to come back up to pressure. It would get there, but slowly. I did drive it, just for giggles, but it showed the same problems from before, only worse. Anyhoo, that part's getting marked "defective" and sent back.

Experiment #2 was to try a used HFCM from eBay. for $150 and a 90 day warranty, why not? At this point I didn't really care about time, I don't need the truck right now anyway. As soon as I unwrapped it, I knew it wasn't gonna be good. I could smell varnished fuel. I pulled it apart to at least take a look-see, and found large amounts of what I can only assume was dried up fuel, as well as some rust on the pump itself. It was obvious it had been sitting for a while. They said it came out of a running truck, but my question was "yeah, but how long ago?". I hooked power to it, and it just clicked like it was locked up. Whatever, they were super cool about the warranty, refunded my money and didn't even want the part back. So now I have a spare HFCM minus pump.

That brings us to yesterday. I ordered an OEM one from oemfordparts.com (~$300), but got an email this morning saying it's backordered. Got to looking around, and found one at AutoZone 25 miles away for $340. Done. I'm tired of messing with it. I put that in tonight, and did a deadhead test in the truck before I hooked it up. 100psi almost on the nose. Hooked everything up, regulated pressure is right around 60. Took it for a drive. Same thing. 😡 So I may have just spent $340 unnecessarily. I'm just comforting myself with the fact that it was only putting out 70 before, so it was probably on its way out. I did have a gelling issue a couple years ago that probably didn't do it any favors.

So now I'm looking at either an issue with the regulator, or a supply issue. I think I'll go get some long hoses tomorrow and try to rig up my can as a temporary fuel tank. If that fixes it, I'll be dropping the tank, otherwise, probably a new blue spring kit.

Finally, she's fixed.

I did like I said, and tested with a can to eliminate anything on the tank side as a possibility. No change, so I figured it had to be in the regulator. Finally got the new OEM one today, and put it in. You know how we mechanics always say we'd rather find a problem, no matter how big or small, than to chase our tails and not be able to figure it out? Yeah, I had one of those "Yep, that's it" moments. Take a look at this... old on the left, new on the right. Notice something missing?

So, one of two things happened. Either I didn't put that seal in when I installed it, or the kit I got didn't have one. The former is entirely possible, but I suppose I'll never know. Whatever, it's fixed now and I'm glad. Spent too much time and money on this one.

To anyone with a similar problem reading this in the future, check this first!

Thank you all for your help! The brains around here are something else. I try to contribute when I can, but usually one of the big brains shows up and I figure I'll yield the right of way.