Acceleration issue....Fuel Pump?

[scenario]

Recently I have had an issue of losing power when "getting into it" with my 86 SVO. Only happens when there is load on the engine (i.e. accelerating, it will NOT happen just revving at stop).

My gut tells me its the Fuel Pump. I noticed the FP is not as pronounced in the sound it makes as it used to be. I do have a prob starting vehicle where I try to start and will just crank and crank. On the second try it starts up. This particular starting issue has been going on for the last 7 or 8 thousand miles and other than that has not been a problem.

I hooked up a fuel pressure gauge and I get no more than 32PSI at idle. No difference if the vacuum is hooked up or not. When revving engine in the driveway the fuel pressure will not go over 36PSI.

I changed the fuel filter and have no difference of 32PSI at idle but did get near 40PSI but not quite when increasing the RPMS.

I did not monitor the gauge while driving bc I have to figure out a way to monitor while driving with it hooked up.

My gut still feels like its the fuel pump????


Any ideas?

Frank V

[svono50]

Either fuel pump or the regulator. You should see a pressure difference when you disconnect the regulator from the intake, where it should increase a few psi. Some of the test gauges have a long enough hose to allow the gauge to lay on the windshield and you can observe it when driving...just make sure you tape it to the glass so it doesn't fall off!

Since you mentioned about disconnecting the vacuum line from the regulator and didn't mention fuel coming out of the regulator line, then we know your diaphram is still intact. Do you have a vacuum/pressure hand pump (i.e.- Mityvac)? You can apply different vacuum and pressure to the regulator to confirm that it is functioning properly.

One other question, does the fuel pressure hold pretty steady when you shut the car of or does it drop of quickly?

[scenario]

It drops very quickly

[scenario]

If it ends up being the pump does the fuel tank need to be dropped or is there an access panel in the trunk area?

[ChrisCurtin]

If it ends up being the pump does the fuel tank need to be dropped or is there an access panel in the trunk area?

You have to drop the tank.

Make sure you get a replacement fuel filler neck gasket before you start. 100% chance you will rip the old one when you try to remove the fuel filler neck.

Also take a look at the gasket to the floor on the filler neck and replace it as well if it looks bad.

[scenario]

I did not get any fuel coming from the hose that goes to the regulator. As it was idling I noticed only a slight stumble when disconnected but no fuel leaking.




ALSO: Any recommendations on a replacement fuel pump?

[ChrisCurtin]

I did not get any fuel coming from the hose that goes to the regulator. As it was idling I noticed only a slight stumble when disconnected but no fuel leaking.




ALSO: Any recommendations on a replacement fuel pump?

I got mine here:

http://www.autoperformanceengineering.com/html/fpapps.html

FPF002

Beware of knock off Walbro pumps. Lots of them on eBay etc.

[MikeFleming]

Fuel pressure is not related to engine RPM, only to load. The only accurate way to test fuel pressure (FP) is with significant flow and under boost pressure. It's easy to simulae the pressure using a MitiVac or similar, but the flow rate is too low at idle to determine if the pump is good. Obviously if it fails the pressure test under no flow, then it's bad but that gives you no idea if it can deliver the required fuel flow when under load.

With the engine idling, or not running with the key on and fuel pump(s) on, there should be 39-40PSIG showing on the pressure gauge with the vac/pressure hose disconnected from the regulator or manifold fitting.

Then the car needs to be driven (unless you have a way to take off the pressure feed line at the fuel rail and measure flow rate and pressure with the pump(s) on) with the fuel gauge visible - best to have a passenger read the gauge while you are driving, or vice versa. Much safer with two people.

Pay no attention to closed throttle readings for now. et to 3K in 3rd and mash hte throttle while the observer watches the gauge and compares it to boost pressure. There should be a 1:1 relationship between boost and fuel pressure with the FP being 39 PSI higher.

Boost = 5 FP; = 44-45
Boost = 10; FP = 49-50
Boost = 15; FP = 54-55
Boost = 20; FP - 59-60 (Do not recommend testing this high if a fuel flow issue is suspected.

If the values are too low for FP, you should replace the fuel pump.

[DaveS]

ALSO: Any recommendations on a replacement fuel pump?

I'm assuming you do not have a pump on the frame rail with the following post...Bosch N69124. Also, replace the in-tank filter (Delphi FS0052). This is assuming a stock configuration. Also, as has been noted replace the fuel filler to tank gasket (Ford F4AZZ-9072-DA), and the fuel pump to tank gasket. I'd also remove the fuel level sending unit and replace that gasket also (same as fuel pump to tank). I also clean out the inside of the tank to get all the old gunk out (most that I have done have been clean). If you suspect your sending unit is bad, you can now get repops from Fox Mustang Restoration (http://www.foxresto.com/SVO-GT-Turbo-Charged-Fuel-Sending-Unit-p/4883010.htm).

I know, lots of info, but if you pull that tank you might as well get it all done. I'd set aside a half-day to do the job without being rushed. I've done it in 1-2 hours before, but that was a bit too fast for my liking.

[scenario]

Thanks

I ran the car with the FP gauge on the windshield. While boosting I get no considerable increase in fuel pressure. Idle is 32PSI and rises to about 36PSI, at around 15 lbs boost it actually drops off a bit and vehicle struggles to accelerate.


Never at any time do I get 40PSI of fuel pressure

Fuel pump is bad?

[svono50]

Most likely it is the fuel pump, but I would not completely rule out the regulator. A quick drop in fuel pressure could be either a bad regulator or a bad check valve in the pump. You can pick up a regulator for about $20 and you can change it a lot easier than the pump. Personally I would start there and if no change, then the pump is your next step.

Chris' recommendation is who I would recommend as well, APE is well aware of the counterfeit pumps on the market and will ensure that you are getting a real Walbro unit. Depending on your plans for your car, you can go with either a 155lph or 255lph high pressure unit, obviously the more HP in your plans the larger the pump.

[MikeFleming]

Never at any time do I get 40PSI of fuel pressure That right there is a BAD sign. STOP driving it under ANY boost.

Most likely it's the pump (85%), could also be the short "S" hose between the pump and bracket (5%), a clogged sock at the base of the pump (5%), a bad regulator (maybe 8%) or gremlins (remaining percentages). THe check valves only have an effect when the pump is switched off - pressure is not held (same symptom as a cracked S hose).

For gremlins I usually use a large bag of salt, pour a continuous circle and light some candles. The artwork is the height of the salt circle and placement of the candles. Do not step on the salt, btw.

For the other issues it's part replacement time. ANYTHING in the tank (pump, sock, S hose, etc) should all be replaced at the same time. The new pump will have a new check valve in it too. Most pumps come with sock, S hose and clamps.

[svono50]

Mike has very sage advise, as you go lean very quickly not getting any additional fuel to the injectors and bad things are certain to happen at that point. I had forgotten about the s-hose splitting, this is certainly a part that has been pretty well know to be an issue on Fox fulie Mustangs.

I can say that the APE pump kits come with all the little bits you need for the install, including new duckbill clips, in tank harness, etc. Just checked their site and the 155lph kit is only $86, so not bad at all. Let us know what you find.

[scenario]

I replaced the fuel regulator with an autozone $20 unit. I also put a new vacuum hose from it and to the intake.

NO CHANGE

I will ride it easy with no boost until I change the fuel pump.

I am running stock and have no intentions of doing anything to increase performance. Would the 155lph pump suffice? It is not about the money bc the 255lph is only like $20 or so more. I have no prob putting the bigger pump in but if it is not necessary than I will not.

[MikeFleming]

Yes, the 155lph will be fine. Iirc the stock one is 88?

[svono50]

At least you ruled out the FPR, unfortunately it wasn't the cause. No reason for the 255 unit if you aren't shooting for some higher HP numbers. The 155lph unit is plenty to handle even a decent bump in HP if you eventually do something. Nice thing about the APE kits is that they come with all the items you will need on the inside of the tank.

As others mentioned, you should have a spare/replacement filler neck seal along with a replacement seal for the pump plate. Don't forget to use a non-sparking brass drift punch to remove the locking ring on the pump bracket. The tops of our tanks can get pretty crusty (see pics), so loosen up as much crud as you can and vacuum it out of the recess before removing the fuel pump frame. I had purchased new locking rings and gaskets from LMR back when I did my upgrade, as you can see the new clean ring in the second pic. Good luck with your project.

7257

7258

[scenario]

Ok, parts have been ordered. I will update with results in about a week or two.



Thanks for all the help!

[scenario]

New Fuel Pump installed. I got the Walbro 155lph unit. Problem seems to be solved Pulls nice all the way up through the powerband.

A little blurry but the maximum Fuel Pressure achieved in the video was just about 59PSI @ approx 18psi to 19psi boost and before it started boosting it hovers about 32psi.



https://www.youtube.com/watch?v=jX-K5-rS2Pk

[MikeFleming]

Glad to hear it's fixed and running like an SVO agian.

BTW - Video is private.

[scenario]

Video should be viewable now

[svono50]

Nice work! Glad to see you got it fixed before you head gasket took a vacation.

[TheSVOTrust]

Thank you for posting, updating and posting FINAL results!

THIS is how a "help thread" should work. It serves to info all and shows that you did the work as suggested.

Mark