7.3 help

toyota1

toyota1

Well-Known Member
Joined
Apr 17, 2008
Location
Fort Mill, SC
My tow pig is a 99 f550 c&c 6spd 220k with a flat bed. It has developed a random no start and i have gotten to the point of throwing parts at. The issue started out of the blue and as soon as i hooked my scanner on it started right away like it should and this is what it does everytime it doesnt start, not slow to fire or missing when it does fire off.
New parts are
Adreniline hpop
Ipr and connector
Icp
Cps x4
Everything fuel related
Injector oring, wiring and gp
And soon to be cps and icp connector

Mods
Php hydra
Bhaf
4" turbo back
Walboro pump
Fpx

I cant figure out what makes it fire up instantly when the scanner is hooked up. Any help would be appreciated
 
Does engine temperature matter at all?
 
Had a problem of my 2000 7.3 no start threw parts at it couldn't figure out end up taking it to a diesel shop was IDM (injector drive module) also had a wire that had rubbed on valve cover on driver side possibly shorted out the IDM
 
Nah temp doesnt seem to matter ambient or engine. Ive got a known good idm im going to try next chance i get
 
Yeah ive tried 4 new motorcraft cps's no change but im going to replace the connector since the tach doesnt move on a no start crank and i couldnt be unlucky enough to get 4 bad sensors
 
whats the battery voltage? If it does not have the correct voltage I can't remember what it was 10.5v I think. You will have no start. I had random no start like that with my 2000 7.3 turned out on of my batteries was dead.
 
I had one I was working on almost the same issue I had pulled the injectors to replace orings and the injector harnesses had injectors tested and they came back all good. Put everything together same issue and everything else checked out fine. From some advice from a ford diesel guy I replaced the injectors with new ones and it still runs like new 4yrs later.
 
fordwheelinman said:
Does plugging the scan tool up make it start, or actually connecting it to the vehicle and checking for codes?

Sent from my D6708 using Tapatalk
Click to expand...
No literally just plugging any of the tools to the obd2 port makes it fire up right away dont even have to turn the scanner on
 
I may try new injectors i just didnt want to spend the money if its a $50 part
 
toyota1 said:
No literally just plugging any of the tools to the obd2 port makes it fire up right away dont even have to turn the scanner on
Click to expand...
I am going to say you have an intermittent network, module or ground issue. I will look at some diagrams at lunch (Ford diesel tech, I have the manufacturer diagrams) and see what I think is going on and I'll give you some thoughts later.

In the meantime, if it happens again check for ground at the DLC, should be pins 4 and 5. It might be one is intermittent and plugging up the scan tool grounds the bad one to the good inside the scan tool harness.

As a side note: not long ago I had a focus in the shorthand setting the alarm killed the TCM on the network, but running a network test would wake it back up. Granted your 99 is much less interconnected with almost no multiplexing compared to that focus, but there are still electronic modules on in, and they are just as unpredictable as a pregnant woman.

Sent from my D6708 using Tapatalk
 
May want to look at the valve cover gaskets/wiring.
 
toyota1 said:
Wouldnt be the most ghetto rigged thing ive done to a vehicle! The thought has crossed my mind to get a cheapo and put it under the dash haha
Click to expand...
Prefect reason to buy a scan gauge or edge cts.

Sent from my SAMSUNG-SM-G890A using Tapatalk
 
Seriously, though. I'm going to throw my vote in with "bad ground." I font know much about these trucks, but if there's a bulkhead connector at the firewall, look there for corrosion. Fords are already notorious for that.
 
The way I see it is there's only 3 circuits in the dlc that could have any effect on starting what so ever - 2, 10, and 13. Those pins are the only pins with a direct link to the pcm. ISO link (pin 7) bridges the other modules to the scan tool.
I think I'd throw a break out box and scope on the 3 main circuits, attempt to start the truck - then plug in the scan tool and look for any variances. I'd vote we're missing something here - are you sure the scan tool is related to the starting condition? Is the scan tool connected to external power and ground or pulling power and ground from the dlc?

Sent from my SM-N910V using Tapatalk
 
The maxi is powered by the truck and the ae and otc and powered by external sources.
To put in perspective to how random it is i cranked the truck after sitting two days yesterday cranked fine, then i shut it off and walked into cabelas for 20-30min cranked fine there went back to my house for 10-15 and had a no start till i hooked up the maxi then went to friends house for 2hrs and cranked fine.
 
toyota1 said:
The maxi is powered by the truck and the ae and otc and powered by external sources.
To put in perspective to how random it is i cranked the truck after sitting two days yesterday cranked fine, then i shut it off and walked into cabelas for 20-30min cranked fine there went back to my house for 10-15 and had a no start till i hooked up the maxi then went to friends house for 2hrs and cranked fine.
Click to expand...
It may be a wild goose chase , buy I'd be interested to see if the key on ignition voltage is present at the ecm is present when it won't start.

Sent from my SM-N910V using Tapatalk
 
Yeah ive wondered if the ecm is getting power but its a pain to diagnose anything because it is so random. I planned to spend a day with it last weekend and couldnt get a no start till yesterday.
 
toyota1 said:
Yeah ive wondered if the ecm is getting power but its a pain to diagnose anything because it is so random. I planned to spend a day with it last weekend and couldnt get a no start till yesterday.
Click to expand...
I figure it's getting it's fused b+, but I can't help wondering if the key on ignition b+ isn't present. The way I'm theorizing, if the constant b+ wasn't present it wouldn't run regardless. The scan tool would make no difference. From my past experiences the main functions of the ecm/pcm are fed by the constant b+, and the switch b+ is used as a "wake up" and may be used for some aspects - but primary functions seem to operate without the switched circuit. I remember a vehicle some time back, that for whatever reason the pcm wouldn't communicate or function until a ccd (dodge obviously) message was sent from another module. After chasing my tail for a bit I found that the ignition switch would provide 12v, but when loaded the voltage would drop to less than 5v due to internal resistance. Replaced the ignition switch and everything worked normally. Plugging the scan tool in, sent a command to the ecm which would "wake" the ecm up.
Checking powers and grounds to the ecm in my book is key in an issue like this, but as you mentioned, it's only useful if it is experiencing the symptom when you test it!

Sent from my SM-N910V using Tapatalk
 
Update in case anyone else has the same problem. I put a blue cps, new cps connector, and new icp connector on and so far that seems to have fixed the problem i noticed it starts up on what seems like half a revolution now vs 3-4 before. I noticed one of the icp wires only had about 2 strands holding it together inside the connector after i took it off. Thanks everyone for the help.
 
It's possible that having the scan tool plugged in was reducing electrical noise just enough to make the faulty CPS get picked up properly by the ECM. Hard to say without putting an oscilloscope on those lines, but it doesn't matter because the CPS was faulty and needed replacing.
 
Back
Top