I'm resurrecting an 89 F150. 5.0 EFI engine runs smoothly once I get it started. This truck has an unknown history other than it has been sitting for several years.

Problem is, the fuel pressure leaks down after sitting an hour or so. Rail holds 41 lb when running. No leaks observed and truck restarts easily when warm. It takes quite a few key cycles to build even 20 lb pressure from cold and even then, continuos cranking to get the engine to catch and stay running. There is a code 63 for the TPS sensor. Will be chasing that today. In tank pump is running.

​​​​​​Does anyone have any suggestions as to narrowing the field when looking for the cause of the pressure leakdown? I suspect this could be injectors, fuel pressure regulator or the HP fuel pump on the frame rail. Single tank truck by the way.

I can start parts swapping, but I like to have a clear diagnosis in hand. Since the engine does not exhibit any symptoms of flooding and runs quite well, I pushed leaky injectors to the back of the list. Hard starting could be aggravated by that bad TPS, but it's my understanding that the fuel rail pressure should hold a lot longer than an hour. I'm convinced it's draining back into the tank and if I am going parts swapping, the fuel pressure regulator will be first on my list.

Any thoughts?

 

TPS fixed the code 63, but no change in the hard starting when cold.

Found a whole bunch of vacuum line issues including no vacuum to the fuel pressure regulator. Will be addressing that.

Thought I'd change the fuel filter, but a surprise was waiting. No inline fuel filter? Single tank truck and I know about the filter in the reservoir, but this is the first one I have seen without an inline filter.

 

Usually a leaking injector will wet the plug or at least stink of fuel. Are they dry and fuel smell free if pulled ~30 minutes after shutdown?

 

My old truck had similar starting issues that turned out to be leaky injectors.

 

Well, the search continues.

I have not found any evidence of wet plugs and there certainly are multiple issues that I am trying to resolve. I am refurbishing a fuel rail and injectors that should take care of any problems with those components. Still, I have uncovered and am resolving several issues.

The nylon vacuum lines were brittle and broken in several spots including the line to the fuel pressure regulator. I have replaced these lines.

The cap, rotor and wires were in poor shape. Replaced as well. Plugs are old, but usable. I'll stress that once running, the engine really does run well.

Full fluid changes will happen before this truck goes back in service. There is no evidence of fuel in the oil.

The in tank pump was running intermittently. Cause is the fuel pump/sender connector. Looks like this failure prone part is difficult to source? I came up with Pico part # 5310 PT, but everybody seems to be out of stock. Possibly no longer available?

The ground to the entire rear wiring harness is not solid. Runs through those circular connectors on the L side inner fender well. All the engine compartment grounds are solid, but I see about 3V on what should be a solid ground at the orange wire at the fuel pump/sender connector. Any chance somebody has an EVTM print of this circuit? My Haynes manual just does not cut it here.

 

Some new pumps come with a new connector, be sure to check the details of the pump to find one.

seems like you are on the right track in regard to your leakdown issue. With ancient injectors, it's a good idea to replace them or at least bench check them with pressure to see if they seal.

 

Some progress.

I have not yet fully solved the fuel pressure leakdown, but the rail instantly returns to 40 lb pressure when I turn the key on. Cause was a poor ground to the tail end wiring. This also cause my taillights to be very dim The ground is picked up off the main harness at the circular 3 pin connector on the right inner fender. Cleaning this connector restored a good ground and now my fuel pumps receive full battery voltage. Taillights are brighter too.

The connector for the tank sender was intermittent due to broken clips. A replacement was somewhat difficult to source. I found Echlin FPC100 from Napa solved this problem. Airtex and Standard also have this connector. Pico has discontinued this product.

The truck is still somewhat reluctant to start when cold. It will crank, firing intermittently until it runs smoothly after some extended cranking. Once it has been started, it is easy to restart. Sitting for an hour or more will make it difficult to start again. This does seem to coincide with the loss of fuel rail pressure when sitting, but the pressure builds instantly and the cold engine is not firing reliably even with 40 lbs of initial pressure. The vacuum lines were deteriorated and I have replaced them Once running, the fuel rail pressure settles to about 32 lbs at idle which is much more like it. The cap, rotor, and plug wires were changed with some used ones I had available. This made a significant difference, but still not up to normal standards. The plugs were worn and replaced. This did not make a significant difference and I have ordered new plug wires. I also have another coil to try, but the spark off the coil tower looks plenty healthy.

I have not yet changed injectors, although I am in the process of cleaning up a used set. The old plugs may have had some signs of being wet, but it certainly was not significant. My sense of smell is unreliable, but I did not notice any unusually strong smell of fuel. There is no undue smoke on startup, even from cold. Possibly, injectors will also cause the fuel leakdown, but I don't think there is enough fuel leaked to produce any flooding symptoms.

 

What are good pressure readings for fuel with and without vac line on the regulator? My rear pump just started acting up, hard starting first and now idles fine , revs freely with no load but under load spits, sputters and boggs when in drive. (aod with 5.0). front still works well and planning on rear replacement anyway but want to know good pressures to monitor system.

Geoff

 

Well, things literally got put on ice these last two weeks. We had a very heavy snowfall, which was needed as our soil is drying up pretty good. This is farming territory and all those farmers get kind of grumpy about the weather.

But it brought me to a standstill!

Anyways, 40 lb with the vacuum line disconnected and about 32 lb at idle with the line connected seem to be normal for a 5.0 V8. I understand the 4.9 six runs somewhat higher.

In another development, I started up the truck the other day only to see the fuel pressure die along with the engine. I have resigned myself to replacing the in tank pump mainly because the gauge sender proved to be FUBAR.

 

Things do not always progress quickly around here and I'm still on this resurrection project. Believe me, there are a lot of things that can go bad when a vehicle sits for 10 years!

Just to recap, The engine now has new plugs and wires. That resolved a lot of the difficult starting issues and I began to ignore the pressure leakdown. I did change the in tank pump and sender, (with a used unit) and this made an immediate difference in how quickly the engine would start. I did not change the injectors or the fuel pressure regulator. I lent my pressure tester to my son and I'm waiting for it to come back, because I suspect my fuel line pressure troubles are not over.

The truck did run fine, but now, after a period of running, the engine will run rough and lose power. Code 41 will show up. (lean O2). The engine will run fine when cold. I reckecked my findings of a poor ground to the rear wiring harness and I proved that I do not have a voltage drop in the ground circuit. Everything ground runs through a single pin, (grey 3 pin circular connector). Somewhat underengineered in my opinion, but there really is not a lot of documented failure here. I did try another frame mounted pump, (used, known good), but this produced absolutely no change.

So, I'm back to the in tank pump. This truck is a single tank model, so I don't have the option of switching tanks. I'm getting pretty tired of dropping the tank, so I'm going to spring for a new pump and sender as well as the connector. I was going to replace the fuel filter, but lo and behold, there is no inline filter on this truck. I'm speaking of that familiar canister post the HP pump. Being a single tank truck, the reservoir is not dual function like the twin tank trucks, but there still is a reservoir and I believe it holds a filter. This seems to be something pretty controversial as I read in this thread.

https://www.ford-trucks.com/forums/1...el-filter.html

So, finding a single tank reservoir canister looks to be pretty difficult. I'm going to try to open this one, but I'm pretty leery of damaging this unicorn. I am considering scrapping the dual pump and reservoir in favour of a 90 and up FDM. Test fit some used parts and I think this will work

The dilemna becomes order the original in tank pump, or an FDM?

 

Did you squeeze the fuel return line closed to eliminate the FPR as far as the quick F-Pressure leak down ?

It maybe the check valve in the HP Fuel Pump, if so, you could add a check valve along with an in-line fuel filter....