I would also say check the lift pump...........

Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.

 

Went over to my buddy's house and pulled the spare pump & lines on the way home tonight. Looks like it is in better shape than the one that's on the truck. Throttle turns smoothly. Pump rotates easily. The linkage for the timing advance isn't worn like my other one was (before I shimmed it) - it starts moving in with even the slightest rotation of the throttle.


Only problem with it is it is a LOT dirtier - especially in the area where all the injector lines connect. I know I don't want to start cracking lines loose with all that dirt on 'em. So, here's my plan....

Pour about a quart of gasoline or diesel into a 12x16x4" deep plastic dishpan as a cleaning solvent & then set the pump, lines and all into it. Use an old toothbrush to loosen all the gunk being very careful to keep the open ends of the lines OUTSIDE the pan and away from the dirt.

Once the worst of the gunk is off, dump out the old solvent and clean the dishpan, then pour in another quart of clean gas or diesel. Once I've cleaned it all up and rinsed it all down nice and clean, THEN I'll remove the lines. Dump and replace the solvent with another quart of clean fuel and pour some of it into all the ports and fittings, work the pump a little, then dump it out. Use compressed air to blow the solvent and any dirt it picks up out of all the fittings. Lastly, install the lines off my pump.

I know that gasoline will work better to clean and degrease it, but I'm not sure it will it be OK for the pump - or should I use diesel? Maybe squirt a little Diesel Kleen in all the ports and fittings to lube things up good before putting the lines back on. Sound like it would work to clean 'er up and get 'er ready to install? Anybody got any other suggestions?

 

Well, I haven't done as thorough of a check as what you're describing PLC7.3, but did push in the shrader valve while it was idling and the problem was at its worst. The flow was good enough that I'd bet it would put out the 1/3 pint in 10 seconds like you describe - even without removing the valve core. Don't really have any way to test the pressure since I don't have a guage. Although I haven't checked it in detail, I guess it couldn't hurt and would only take a few minutes to do.

The one thing that makes me think the lift pump isn't likely to be the problem, is that it runs OK for a while, goes to crap, then works OK again after sitting. The longer it sits the longer it will run OK before crapping out again. Isn't the lift pump just a mechanical diaphragm pump? Pretty simple device, and I don't quite see how the heat up / cool down cycle could affect its operation and make it act like that. Is there something about it, the way its made, or the way it works that I'm missing here? Something that would explain the run-time vs. non-run time related intermittant failure?

 

I think most AP stores carry a pressure/vacuum guage for about $15-20, you will then be able to do the fuel pressure and the brake/trans/vacuum system tests.......on your truck.

 

Cool, I'll get one.

But about my question. How/why could/would the lift pump go out in a way to give the symptoms I'm describing. I respect your opinion based on your previous posts and between you and skimballc you've got my curiousity revved up about how the lift pump could make one do what mine is doing......

 

It's just a 'check it cuz it's cheaper' thing. I'm leaning towards the Inj. pump too.

 

Actually, its not just a 'check it cuz it's cheaper' thing, but more of a 'check the fuel system thoroughly before you decide what's wrong with it from its inconsistent symptoms and the online advise of a bunch of yayhoos you don't know from Adam.'

 

Well, first off, the symptoms are pretty consistent. The longer it runs the worse it gets. Once the problem starts, the longer it sits, the longer it works - but it still reverts back to not working pretty quick.

Secondly, while I admit I haven't checked the lift pump thoroughly yet, I have checked it for flow - which looked pretty good. As explained in my first post.

Third, as for the "yahoos" around here and their advice, Spectramac isn't someone "I don't know from Adam". He works on diesels for a living, and I have met the man in person. What's more he's already given me a spot-on diagnosis for two or three problems - over the internet - before I ever even met the guy. Then he drove 30 miles to meet me, brought along his timing adapter, and helped me time my pump - for no charge - just because he's such a nice guy.

No offence man, but I've explained several reasons why I think its the IP. However, I'm still wondering about the logic behind your theory. How could a mechanical diaphragm pump - specifically the lift pump - give the kind of running-time vs. resting-time symptoms I'm seeing? I don't get it and you seem to be ignoring the question. Instead of explaining why you suggest that as the cause of the symptoms, you almost seem to be trying to take a shot at everyone else here - including me I guess.

Lets keep it civil and constructive, and present the reasons for our theories in a neutral, logical manner. No need for getting upset or slamming anyone else.

Lastly, I'll follow my own advice and present two more logical arguments for it being the IP.

First, I noticed my idle speed was low a couple of weeks ago - down around 450 RPMs. I adjusted it up to where it should be - around 600 RPMs and it stayed like that for a week or so. Then last weekend I noticed that it was back down around 500 RPMs again. I adjusted it up again and within a couple of days it was back down to 500 RPMs again. To me that seems like another indication that the pump isn't pushing the fuel based on its throttle position, the way it is supposed to.

These pumps are just an 8-piston variable displacement mechanical pump, most likely a variable pitch swash-plate design. I havent had one open to verify that, but based on how they are constructed externally, and what they are supposed to do, that is what they appear to be. Basically they vary the amount of fuel they pump based on a variable piston stroke that changes as the throttle lever position changes. As the throttle is opened the stroke of the pistons gets longer causing the pump to push more fuel per revolution out through each injector line. My theory is that the mechanism that varies the piston stroke is worn, so as it warms up the pump doesn't push as much fuel per piston stroke as it should. That is what I think is going on with my pump. The fact that I've set the idle higher - which just amounts to opening the throttle a little more with an adjusting screw - and it doesn't stay is evidence that the internal mechanism that adjusts the piston stroke length is worn out.

The second additional new reason I'll give to support my IP theory is that last weekend when I was messing around with adjusting the idle speed & the VRV, I tried pushing in the timing advance lever with a screwdriver while the engine was sitting there idling - and it seemed to make almost no difference at all. From what I've read around here, pushing in the advance at idle should make it run MUCH worse. Just for grins I called a very reputable injector & pump shop here in my area and asked "if there is a way they can test my pump while its still on the truck?" Guess what they said? The guy said to try depressing the advance lever with a screwdriver. If the engine runs really bad the pump is probably not the problem. If it doesn't seem to change much or at all, then there's a pretty good chance the pump is probably bad.

FWIW, if I can get my hands on a fuel pressure guage I will check that first thing tomorrow before removing my pump, just to show that when I ask for advice I don't ignore it. Even if I can't get hold of a guage, I will still check the flow rate as suggested. Dollars to donuts, I'm going to find it is fine - even if I run it until it warms up and starts acting up first.

Sorry this post is so long - sometimes I kinda' get carried away....

 

Oh, and I almost forgot. Anybody got any thoughts on gas vs diesel as my cleaning solvent for the pump?

 

Stick with diesel. You don't want any gas getting into the pump.

 

You mean some Yayhoos from TN with 20 posts under their belt?

I'm just pullin' yer chain! You know how may IPs I've changed? Heck, I can't even remember! But I can tell you I've only changed a few lift pumps.

 

Ah, fellas, you miss the tongue in cheek nature of my post in that I include myself as a friggin' yayhoo. Besides, I did agree with "it sounds like the IP", and I am merely suggesting that you check out the lift pump too before tearing **** apart. I will concede that this isn't the usual IDI forum I visit. Cuz y'all are all crazy. If this thing would allow me to use those silly face icons when I try to, there would have been one after the last sentence and in my previous post that irked you. So it goes.

 

Nah, not irked at all, just wanting to keep things on the level and logical.

Your emoticons problem is weird.
I can put one wherever I want LOL!

Well, I finally found a fuel pressure guage for under $50 at Harbor Freight.

Started 'er up everything seemed fine. So I let it idle till good and warm. Problem came back - which I expected.

So, I shut 'er down and tested it as instructed. With the Schrader valve core removed the needle on the guage pulses, but was definitly going above 4 psi. 10 seconds cranking pumped just over 6 ounces of diesel into my measuring cup. So much for the lift pump theory.

Glad I came in and checked the board Spectramac. I already washed down the OUTSIDE of the pump (lines still attached) with gas, but haven't gotten any inside. I'll siphon some diesel out to do the final wash and to pour into all the ports and line fittings. Thanks for the reply man.

I'm off to go pull my pump and get back to it. Should be able to report some more progress in a couple of hours...

 

We are all crazy?

What makes you think something like that?
Is it my picture?
That is just my snow plow hat,

I am the joker in the snow plow that waits for you to finish shoveling the driveway so I can plow it shut again.

This is something like an extended family.
There are a few black sheep like me, a couple shining nights on spotted horses and several other regulars that are somewhere in between.
Several countries are represented and we all get along fine.

Yes we get off topic rather often, but so do conversations that almost everyone I know has.

There is no other IDI Ford site as far as I am concerned.
The information that is freely offered in this forum is incredible.
The people here will answer the same questions hundreds of times every year, and do it nicely.
There is no part of an 83 thru 94 Ford diesel truck that someone in this forum can not answer a question about.

I was honored when I was offered the moderator position, I am also very proud of all the members of this forum. They make my job here fun and easy. I actually look forward to getting home every evening and reading all the posts for the day.

Malcolm, just swap the engine, that way you get a fresh lift pump and IP and injectors.
Are you washing away yet? Is the water at your front door?
I watched the news yesterday morning and it looks like you all have had enough rain for a while.

I now return you to your regularly scheduled programing.

 

Yeah Dave, you're no black sheep. You're one of the white hats as far as I'm concerned. Couldn't use you as an example in my reply to skimballc though - cout the ause we've never met.

I couldn't agree more about your general comments about the forum & its members. Great bunch. And with mods like you around to to help cool tempers and (if necessary) edit any posts that go over the line, I expect it will stay that way. But enough of that.

I'm done for today, but unfortunately I can't claim total success. I got the spare pump all cleaned up nice and it looks almost new. I swapped the lines from my pump onto the spare, just 'cause I know mine are in good shape and the ones that were on the spare are an unknown. While I had everything off & out of the way, I decided to do the compression check. First 3 went great, and I'm happy with the results so far. showing 430, 450 & 475 psi. Not bad for a 20 year old motor with 200k on it!

Unfortunately the cheapo Harbor Freight compression tester blew a gasket on the 4th cylinder I tried to test. SO, I'm at an impasse. I don't want to put the pump on until I have all the injectors swapped, and I don't want to put any of the injectors back in until I finish the compression check. Its so much easier on the starter and batteries that way.

Oh well, I'll get right back to it tomorrow morning - soon as I exchange the compression tester.......