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Discussion Starter · #1 ·
Ok guys I'm a fair shade tree mechanic but stumped. Got a 1995 7.3 turbo 5 speed 268k. Started truck drove about 1/2 mile when I started up a slight incline truck started losing power like it was out of fuel. I turned around drove back to house put in 10 gallons while it was still running & continued my trip. It did the exact same thing at the same place. Turned around & it died half way back. It would not start so towed it home.
I had noticed a slight drip underneath on the passenger side at the back of the engine which I now thought must be the lift pump leaking at the weep hole. This would be consistent with my problem.
Changed fuel filter cleaned the bowl & fpr. Blew air thru bowl,supply,return & fuel rail lines to confirm no plugs. Put fuel in bowl & primed .Still no start. Yes I have good batteries! Tach was moving a little , wts light was working & check engine light flashed as I turned key then went out. Pulled the plug on the icp. IHOP had oil to the top plug still Nothing. Ordered new lift pump & when arrived installed. No fuel to bowl while cranking after priming. New lift pump bad out of the box.
Ordered another from different source & installed. Same as before but now no Tach movement or high pressure fuel & check engine light stays on while cranking. Thought cps so put in my spare. No change. Fast forward 4 different cps (grey,blue & black). No change. Ordered new Ipr & installed. No change. I have the OBD2 that has NOT been flashed so can't get any codes. As a last resort I tried a shot of starting fluid. Nothing. Didn't even try. No smoke just cranks. Checked all connections. Now I'm thinking cps voltage but nope. Got 12 volts a to c. 5 volts b to c. Checked both relays for pcm & icm & ALL FUSES WITH METER. Fuel bowl heater has been removed & unplugged. Fuse 22 is good. The only thing out of ordinary was the power to relay 2 (icm) has 10.5 vdc. Relay 1 has 12.8vdc. relays are good but tested all 4 then swapped out 3&4 to 1&2. No change.
I am 50 miles from any town & have limited test equipment. So I am about at the end of my rope.


At this point what is strange to me is no Tach & no high pressure return fuel & won't even try with starting fluid. The only warning I got was the slight fuel drip before all this. It was running fine.
 

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Discussion Starter · #3 ·
cam sensor?
Thanks for the reply but as I said in my post I tried 4 different cps's. The last 2 we're ford oem & IH brand new.

I have done the cps thing 3 times in the past & it got me up & running but nothing this time. I don't know what else would case a no Tach on a 1995.

Kinda why I'm stumped.
 

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Check the wiring from the CPS plug all the way back to the PCM plug. Look for shorts to ground/to the other wires and open circuits (well one will be the ground, but it should be an isolated ground that ties directly to the PCM). I would also check the IPR circuit. Next with KOEO, I would check the 5 volt reference power that provides power to the various sensors. No 5 volts no sensing.. anything. The lack of 5 volts could be a short somewhere or a non-function PCM (I usually try everything before going after the PCM). The 10.5 volts on the IDM is a little worrying. I would follow the IDM power back until you find where your losing voltage. Somewhere you have a poor connection that is acting like a resistor.

Cj
 

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Discussion Starter · #5 ·
I appreciate the reply Cj. cps voltage 12 volts a to c. 5 volts b to c so getting power & wiring looks fine.

I also installed a new Ipr with no change. Even changed the pig tail. No change.

I have had cps issues in the past but not like this.

It's just not consistent with my initial symptoms. It acted like it was low on fuel going up a small hill but would still idle. Went home & put in 10 gallons and it did the exact thing in the exact place only died this time on the way back & has not even burped since .As I posted everything pointed to a bad lift pump.
I have put two new lift pumps now but still not getting fuel to the fpr from the high pressure side. Blew line & they are open.
 

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Apologize, forgot I read the cps part. One think I’m considering is a new engine wiring harness for my truck as preventative maintenance, might be worth thinking about. Also, this doesn’t explain your tach issue but Could it be the filters inside the tank gummed up and not allowing enough fuel? And what about oil pressure? I recently saw where the low pressure oil pump was failing and the truck would crank all day but no start, I know that’s kind of a stretch given your fuel symptoms but hard to say. Given all your electrical checks, it almost points back to something like that.
 

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I appreciate the reply Cj. cps voltage 12 volts a to c. 5 volts b to c so getting power & wiring looks fine.
It is my understanding that the CPS should not ever see 12 volts or kick out 12 volts. The CPS is a 3 wire sensor - ground, +5 volts (from the PCM), and signal return. I wish I could find the source PDF... but as you can see, you should not have 12 volts on any 3 wire sensor on the engine. Here is a screen shot from the (for lack of a better term) 7.3 early to late migration manual:
Schematic Font Parallel Engineering Rectangle


As you don't have the ability to plug into the PCM and pull data, troubleshooting is going to be more difficult. It might be worth while to have Ford update the PCM or send it out to Diesel Technology of Chattanooga for a reflash so that you can use the OBD port in the cab. You will need FORScan, a laptop computer, and a good adapter - I like my OBDLink SX, but there are wireless options as well that will work with FORScan Lite (phone version). As long as the reservoir for the HPOP is staying full, the LPOP is fine. Have you cracked a line on the high pressure fuel line side to relieve the air? I agree that figuring out the fuel situation is first. I'm not sure why the engine wouldn't kick over with ether. I do know that the PCM won't release the IDM to fire the injectors until it sees 120 rpm and 500 psi oil pressure on the ICP. If the CPS is not returning good info you won't be firing injectors. You can fool the PCM by unplugging the ICP (PCM assumes 500 psi in the high pressure oil rail).

Cj
 

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Discussion Starter · #8 ·
Thanks guys. Nice schematic! Oil pressure was always good. Not sure why I'm getting the 12 v to the cps but still getting the vref 5 v & good ground. I have unplugged the icp no difference & no oil in it.
I have cracked the high pressure fuel lines at the fpr & just get a drible. I disconnected both & Blew air thru both. Fuel shot out the other line. So to me that says the fuel rail lines are open. Dropped the tanks & no obstructions. Even bypassed the fuel selector & confirmed ALL line ( supply & return are open). I am 65 miles from a dealer so can't get it to one for flashing the pcm.
No of this makes any sense that it wouldn't at least try with a little shot of ether.
 

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There is a little filter screen somewhere on/in the filter housing that can become plugged up. I know there is a post or two about it here on PSN with good pictures, but I can't seem to find it at the moment. Here is a different one: FPR Screen keeps filling up
Not that I recommend using ether on a diesel engine, but a very slight shot of ether may not be enough to kick the engine over. Could be you had too little a ether shot.
 

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Discussion Starter · #10 ·
There is a small round screen on
the fpr where it attaches to the fuel bowl. Its clean. In fact I disassembled the fpr and
cleaned. I gave it enough
Ether ( after disconnecting the
Gp).
 

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@Patrick Feeley has a nice diagram of the fuel path... hopefully he'll pop up and post it.
 

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Discussion Starter · #12 ·
Thanks again. I have a couple but still doesn't show exactly how the fuel & air get into the cylinders. If it's a closed system then it would make sense that neither air or fuel could enter the cylinder unless the injectors allowed it. That could explain why it wouldn't even try with ether.
I have litterly spent weeks searching the web for the same symptoms to no avail. In fact I haven't found another case where it won't try with ether so kinda leads me to think there is nothing preventing air from getting into the cylinders. If that is the case it would have air & fuel only lacking combustion to fire. That would mean a catastrophic failure & no compression. Not at all what happened when it had the problem.
Everyone raves about the 7.3 but without the ability to pull codes my experience is it's very difficult to keep it running.
I checked out the site recommended for the idm & pcm but they are asking about $500 each.
I am trying not to throw more good money after bad on a truck that's almost 30 years old.
Seems like someone would have made an app to flash it from the phone to the OBD2 by now.
 

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These diesel engines are really not much different than a gas engine except that the depend on compressed fuel to ignite instead of a spark plug.

The fuel gets into the engine through the fuel injector which is controlled by the PCM and IDM. Air gets into the cylinder through the air intake and the intake valves. Same as a gas engine that is running fuel injectors.

I have no idea of why it didn't fire with your either, unless you have a massive air leak on the intake system. Either enters the cylinder directly through the air intake and intake valve and fires off of compression.

However you have a lot of other things that will cause these engines not to run and without a scanner that can read live data you are just shooting in the dark.

Here is a fuel flow diagram, I'm not sure if it is the one that was mentioned but you can get a idea of how it flows.

 

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Discussion Starter · #16 ·
Thanks Bugman. Had all but the psd. The flow chart shows no Tach & it's the cps. I've put in 4 different brands with nothing. It shows with tach no smoke etc. It's the. Lift pump. I've put in 2 new ones. All with no change.
Your description was very informative & indicates the engine should fire with ether (period). There are no leaks on the intake. For obvious reasons I am hesitant to go heavy with ether.

As I'm sure you can tell Diesels are not my strong suite & I appreciate everyone's time and advice.

With everything made in China now days maybe everything I have put in now is bad . But I have a hard time accepting that.
I have ohmed the cps's & get slightly different reading on each but nothing open or shorted. I checked the magnet strength on each and same. I know of no other was to test the lift pump other than it pumps or not.
The 1st one didn't pump at all. And yes the plunger was installed correctly. The second one fills up the bowl although not as fast as I remember. The second stage had fuel in the rail lines to the fpr But no pressure? As far as I know a mechanical lift pump should pump on the second stage stronger than the 1st stage but it's not happening. Is it possible something between the banjo bolt and the fpr holds the fuel up for some reason?
 

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You need to get a scanner onto it to see what is going on when you try to start.

Either FORScan on a laptop or FORScan Lite on a smartphone with a ELM 327 Bluetooth adapter. The laptop version will give you a lot more information but the lite version on your phone will tall you a lot of what is happening.



You also need to check the fuel pressure, I haven't seen it mentioned yet. You can do it with a pencil type air pressure gauge on the valve on the drivers side of the filter housing. Do it while cranking but wrap a rag around it so that you don't spray fuel all over the place. You should have a minimum 20 psi. There is nothing in the system that will block the fuel. The fuel pump pulls from the tank on the low pressure side and sends it through the filter housing, then draws it from the filter housing and pressurizes it to send it to the injectors and back through the FPR and back to the tank.

Also look around in the valley and see if while you were replacing things that something didn't come unplugged. Mostly around the high pressure oil pump. I also haven't read if you have checked the oil level in the HPOP but will all the cranking that you have done it may of ran down. There is a plug on the top that you can remove and then look. Make sure that it is close to 1/2" from the top. If it is low just fill it with the same oil that you use in the truck. It gets it oil supply from the low pressure oil pump.

Also check the battery voltage when cranking. If I remember right you need a minimum of 10 volts for the PCM to fire up, if you are lower than that you'll have a no start.
 

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Discussion Starter · #18 ·
All of this was stated in my original post. Forgive me if I wasn't clear. The scanners don't work on my 1995 as it was never flashed with the upgrade.

More specifically I have tried FORScan Lite on a smartphone with a ELM 327, torque,and many others with no luck. They communicate with the elm327 but not the trucks ecm,pcm or idm.

I am not getting pressure to the fpr (only a drible).

Nothing loose in the valley.

Oil level in the HPOP less than 1/2 from the top.

Battery voltage 12.8 vdc.

Now on a positive note. I tried about a half second shot of ether & got my 1st baby try to start. Also showed apox. .75 rpm on the tach.

I think before I do anything else I'm gonna open the bowl & direct prime the standpipe to fully prime the second stage.

I did prime it with an electric fuel pump but perhaps it didn't have enough pressure to push it thru everything.
 

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No pressure at the FPR means another junk fuel pump, at least in my book.

I don't know if you can switch the lines from the pump to the filter housing but that is something to check.

On the scanners not working with the possibility of the PCM not being flashed would mean that your truck is still OBD I with the connection near the driver's side hood hinge. But that won't give you any of the readings that you need to monitor.

Without being able to use a scanner connected to the PCM you would need to purchase a gauge to plumb into the high pressure oil system.

But I believe your main problem is no pressure out of the FPR

I don't believe that you can prime the high pressure side of the fuel pump since it goes directly to the heads through the banjo bolt.


Sent from my SM-A426U using Tapatalk
 

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I've primed my engine several times by pouring diesel into the filter housing, maybe 2/3 or 3/4 (leave room for the filter) after running a tank dry (before I fixed the level senders). It always starts within seconds of cranking.
 
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