1987 6.9 IDI Losing Prime Overnight

I'm troubleshooting a cold-start issue on my 1987 F250 6.9 IDI. The truck starts immediately when cold, runs for about 2–3 seconds, then dies. After that, it takes several crank attempts before it will start and continue running. Once running, it runs perfectly with no issues. So far I've replaced the injector return lines, return caps, O-rings, injectors, glow plugs, and glow plug harness.

After the truck sits overnight, the fuel filter head appears to lose prime. When I depress the Schrader valve on the filter head before starting, I get no fuel at all. After cranking and getting the truck running, fuel is present at the Schrader valve. I'm now investigating possible air intrusion around the fuel filter head and the fittings shown in the attached photos. These seem like potential sources for air entering the system and allowing the fuel to drain back overnight.

I found this older thread discussing the fuel line olives and related fittings:

https://www.oilburners.net/threads/where-to-get-the-fuel-line-olives.67503/

Since that thread is over 10 years old, I'm wondering if there is a current source for these parts. Has anyone recently purchased these fittings or olives, and if so, where did you get them? Also, has replacing these fittings resolved a similar air intrusion or drainback issue for anyone?

Thanks.

You can get the olives here



Several vendors also offer kits to switch from hard lines to a JIC fitting flex hose to delete the olives.

You sound like you are on the right path, the return system is awfully touchy if you bump into it , it's prone to leak, this gets worse as they age sometimes.
Lube the lines before and after fitting the olives.
Threaded fittings, use rectorseal on the non olive side as some teflon based sealant is going to break down in diesel...
Good luck and welcome to the site.

There's a check valve in the mechanical fuel pump as well thats prone to go bad.....

Make sure your mechanical fuel pump hasn't gone bad. I've had several go south on me and pump diesel into the crankcase. Just keep an eye on your oil level.

I finally went to an electric fuel pump.

Dang Chinese

On my 90 model, I was getting air intrusion in several places. Check valve in the Mechanical pump had gone valve bad, injector caps or problematic, and the O-ring seal around the heating element in the top of the fuel filter was also leaking.

Once I addressed all three of those items, I no longer have a problem with fuel draining down overnight.

I don’t know if you’re 6.9 has the same fuel heater in the top of the filter housing as the 73, but if it does you might want to check and replace those earrings or the heating element itself.

Thanks all for the input! Just discovered that the hard line into my lift pump is leaking (pic attached). The vacuum pump was replaced last weekend. I'm curious if something got bumped during the install or if the lift pump is just the next thing my truck wanted replaced. The last person to own the truck kept a good history of work done to her. The fuel pump was last replaced in December of 2020. I haven't tested the lift pump. I ordered new fuel olives after Nero responded & I'm waiting for them to arrive. While I wait... I'm going to clean everything up and see if I can find where this leak is coming from.

It could be the lift pump itself. Keep an eye on your vacuum. The pumps don't seem to last very long these days.

Will do! Thoughts on which mechanical lift pump to have ready if this one is bad? Carter, Delphi, Napa, etc?

If you're not going to order a NOS Motorcraft pump from eBay, I'd go with NAPA over Carter or Delphi.

If it help, I have a Napa pump on my truck, but it also is from 2011, quality might be different.

Waiting on parts... I snugged up some of the hard lines and used a vacuum pump kit to try to get air out of the lines.
I assume the system should be airtight with no air bubbles?
I bled it 4 times and the air bubbles never stopped. It did get to a point where there were just 1-2 bubbles every squeeze of the vaccuum pump.

Cranking the engine with the Schraeder valve depressed will be a better test for air intrusion. You should have a solid stream of fuel, no spitting or air.

I like to bleed the injectors by the firing order. 1, 2, 7, 3, 4, 5, 6, 8

My truck will usually cough on 7 and start by 3. I probably need to set the timing on that worn out IP.

After you run the truck the first time you can let it sit overnight and check the fuel filter. It should be full. If it's low you know you have air intrusion.