6.9 IDI hard start and idle lope

[seanres]

Early 1983 F350 6.9 IDI that'll only start with ether and has a lope that sounds like not all 8 are firing. Clears up after 5mins or so but every cold start has the lope, lots of white smoke. Smoke clears a bit when on throttle but does not clear up entirely. Thought new injectors would fix it but it persisted. I've spliced a clear line between the return lines and fuel filter housing which shows no air, waiting for a fitting to splice between the lift pump and fuel filter housing. New glow plugs with manual bypass (verified all are at 10v when holding momentary switch), return lines, starter motor, batteries, now cranks strong. Diesel tech friend thinks its stuck rings, so have some marvel mystery oil coming in to eliminate that option (https://www.oilburners.net/threads/is-marvel-mystery-oil-safe-for-an-idi.37634/). Not sure what else could be causing the issue, really trying to get to the state where I don't need ether to start. Thanks for the help.

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[IDIBRONCO]

How's your timing? If you don't know, try advancing it a little bit and see if that does anything.
I'm also leaning toward your injector pump. Have you tried the ATF trick to see if that helps any? If not, maybe you should do so. I don't want to jump to conclusions yet, but you may have to replace the injector pump as well. Despite the online fallacy, the pump and injectors should be replaced as a set. They wear internally at the same rate. The fallacy being that new injectors will fix most problems.

 

[seanres]

Not sure about the timing. Have not tried putting any ATF in either, will replace the fuel filter which I haven't done anyhow and fill it with ATF and see if it improves

 

[ROCK HARVEY]

My truck had a hard start and identical cold idle to yours, even after new pump and injectors. What solved it for me was deleting the connection between the fuel filter housing and the return lines. It was causing my fuel filter to fill with air, and then the loping idle was the IP trying to constantly adjust to the air bubbles going through it until they were all out. Give it a try, it doesn’t cost anything!

 

[Old Goat]

There was a TSB (Technical Service Bulletin) quite a few years ago
about the problem.
I removed the return line from the Filter to the first Injector.
Have never had a problem eliminating it. Did that quite a
few years ago.

Never spray ether and use Glow Plugs at the same time.
Big NO NO.

A little side note.
Only problem I had, was removing the rubber line off the first
Injector plastic cap, and or cutting it 1 or 2" from the cap to
plug it off with a screw or???
You will disturb the cap and "O" Rings and "maybe" cause it to leak.....mine did.
Then the next one leaked, finally removed the whole side, replaced the "O" Rings, greased them up and snaped them down as one assembly. Took care of it.
You can buy bags of 50 for around $10 from McMaster-Carr.

Don`t know if this is your first Diesel or not. When you remove the Hard Lines, remove the line vibration Clamps, then it help
to prevent the lines getting bent moving them.
Be sure to replace the Clamps, or the Hard lines can crack from
vibration.

Watched your video, and noticed the loping stopped. Iam betting also it is the IP till it warms up.


Goat

 

[seanres]

Strangely enough if you can see in the video I actually replaced the return line to fuel filter line with a clear hose and haven't seen any air while cranking to start. I'll remove and cap it just to see, will be replacing the lift pump to fuel filter line with clear tubing to see if I can spot air anywhere else

 

[Cariboo4x4]

I have similar problem yet not all the time with 1989 F250 7.3 IDI. Lately starting truck up after block heater being plugged in overnight, truck will start up then stall. Or start up and idle really rough with lots of smoke. Other days start up, idle high for bit, then kick down and run great. Also I notice it was starting great in warmer weather, 32 degrees F and idling really rough in cold freezing weather even if it was plugged in (5 degrees F). Also if it sat for a week it would take a long time of cranking before it starts up. I replaced all the 16 fuel return o rings on the 8 injectors in 2022 with Motocraft brand. My research is pointing to a possible cracked rubber return line. Like air intrusion and fuel settling back to tank in return fuel lines. The crack is closed in warm weather and open in the freezing dry weather. I like the idea said on here about removing return line from fuel filter to 1st injector. Water in fuel light came on a couple days in a row recently and I drained water seperator two times now. I’m thinking its not an ip pump or injectors since its an intermittent problem. I don’t understand how air into return lines would cause rough idle or long starts since the fuel is pressureized from mechanical lift pump to filter to ip. Maybe someone can help me understand how air into return return lines affects idle. Just trying to get my head around it.
I was looking to buy fuel line return kit yet don’t want to buy a cheap kit. Only want to do it once.

 

[Old Goat]

I found this thread doing a search for the TSB for deleting the
return line from filter to #1 Injector.
Ford TSB Article No. 92-10-9 May 6, 1992

7.3 fuel system upgrade - Ford Truck Enthusiasts Forums

Pre-Power Stroke Diesel (7.3L IDI & 6.9L) - 7.3 fuel system upgrade - this mod (if u wanna call it that) is used on pre-89 IDIs with the 7.3 (6.9s also probably). Reason i did this was i ordered the wrong return line kit and i was looking for a way to eliminate areas of air intrustion. While...

www.ford-trucks.com

Did a lot of Google searching through threads just to find this one. Lots of mentions of the TSB.

I copied this from tjc transport on Ford truck Enthusiasts.

back in late 88 or early 89, ford issued a TSB suggesting deleting the line to help hard cold starting due to air intrusion.
as my truck was starting to have air intrusion problems, the local ford dealer capped off the line and plugged the filter head.
the air intrusion cold start problem stopped.
the one way check valve in the filter head behind the return line was bad and letting air in. that is what the TSB was about.

To see the TSB you need to have a subscription to alldata.


Goat