1971 Ford 4500 won't start. Thermostart circuit suspected.

MikeMyhre

Member
I have a 71 ford 4500 backhoe that was running fine last year. This year, found the fuel tank empty so I needed to bleed the system. New fuel filter. Air compressor on the tank (gravity feed system) and I bled the lines to the injector pump with good fuel flow.
When I crank the engine, it wants to start, but doesn't quite make it (this is normal if no heat is applied, even in summer).
Looking at the thermostart, it glows hot when power is applied, but there is no fuel in the return line from the injectors (goes through a checkvalve component that vents back to tank).
I even tried using a funnel to supply fuel to the thermostart, but that didn't make any difference.
Realizing that the thermostart could be defective in the fuel flow portion, I ordered a new one which will be here in a few days. Regardless of if the thermostart is defective or not, I still don't have any fuel feeding it. When I crank the engine, I don't get any flow from the return line port (which I would think would be required to get reliable flow to the thermostart). There is gravity flow when not cranking, so I don't think it is an air bubble issue there, maybe it just needs more than idle speed to 'kick in'.
Any ideas what my problem could be?
 

For first start I always open the throttle half way or more, once the engine fires up I idle it back down.
You shouldn't need the thermostart to fire the engine unless it's cold weather.

You may find that giving it some throttle may help it start eveytime.
 
(quoted from post at 14:19:19 08/21/18)
For first start I always open the throttle half way or more, once the engine fires up I idle it back down.
You shouldn't need the thermostart to fire the engine unless it's cold weather.

You may find that giving it some throttle may help it start eveytime.

Normally, I would agree, the 1/4 throttle seems to be the 'sweet spot' for starting. I have tried full, to none while cranking and even moving it back and forth. My theory is that too much fuel takes too much heat away.

I have owned this backhoe for 25 years and it may be lowering compression, but it seems to get harder to get started as it gets older. This is the first year I found it completely dry in the tank. I have needed to bleed it before and due to the gravity feed, it is very hard to start after it loses prime.

Mike
 
Unless you live near the south pole, you shouldn't need the services of a themrostart right now. Sounds to me like you simply have air in
your pump. Did you bleed the pump itself?
 
It is not uncommon on those tractors to require loosing the injector lines at the injectors and crank it over until you get fuel at all 3 lines.

Mark
 
I agree, BTDT many times. You have to remember that while bleeding the lines at the injectors to make sure you hold wide open throttle.
 
(quoted from post at 17:21:16 08/21/18) I agree, BTDT many times. You have to remember that while bleeding the lines at the injectors to make sure you hold wide open throttle.

Good point, I have been bleeding at a much lower setting.
I just went through the sequence again. First at the filter, next at the injector pump, then at the return lines and finally at the injectors. I am fairly certain I have fuel everywhere now.

One of the three cylinders is trying to fire, the other two not contributing much. If the others kicked in I am sure it would start.

I also took off the valve cover today. Watched the valves crank and they all moved as expected.

Tomorrow I hope to measure compression.

Any other thoughts to try?
 
Were the fuel pipe from the filter goes into the rear of the injection pump there is
a filter in the pump and that may be blocked. I have bled a lot of 3 cyl Fords with
no fuel pump over the years and somtimes I have had to give them a quick sniff of
starting fluid. MJ
 
(quoted from post at 02:27:33 08/22/18) Were the fuel pipe from the filter goes into the rear of the injection pump there is
a filter in the pump and that may be blocked. I have bled a lot of 3 cyl Fords with
no fuel pump over the years and somtimes I have had to give them a quick sniff of
starting fluid. MJ
You are talking the pipe opposite the drive end of the pump? Looks like a centrifugal pump outlet port? I cracked that fitting loose and there is no fuel coming from that. Not sure why there would be a filter there when it just came from a filter.
I have tried starting fluid and it doesn't seem to help much (more premature detonation knocking than productive starting).
 
(quoted from post at 19:09:51 08/21/18)
(quoted from post at 17:21:16 08/21/18) I agree, BTDT many times. You have to remember that while bleeding the lines at the injectors to make sure you hold wide open throttle.

Good point, I have been bleeding at a much lower setting.
I just went through the sequence again. First at the filter, next at the injector pump, then at the return lines and finally at the injectors. I am fairly certain I have fuel everywhere now.

One of the three cylinders is trying to fire, the other two not contributing much. If the others kicked in I am sure it would start.

I also took off the valve cover today. Watched the valves crank and they all moved as expected.

Tomorrow I hope to measure compression.

Any other thoughts to try?
Is your battery turning the motor fast enough to build enough cyl heat to fire?
 
Turning Fast Enough?(reply to post at 05:57:17 08/22/18)
Yes. I think so. I am getting all three cylinders to 'squirt' about once a second. At this point, only one cylinder occasionally kicking in. I know the faster it turns, the better chance of starting.

Thanks,

Mike
 
Turning Fast Enough?(reply to post at 05:57:17 08/22/18)
Yes. I think so. I am getting all three cylinders to 'squirt' about once a second. At this point, only one cylinder occasionally kicking in. I know the faster it turns, the better chance of starting.

Thanks,

Mike
 
(quoted from post at 19:09:51 08/21/18)
(quoted from post at 17:21:16 08/21/18) I agree, BTDT many times. You have to remember that while bleeding the lines at the injectors to make sure you hold wide open throttle.


I just went through the sequence again. First at the filter, next at the injector pump, then at the return lines and finally at the injectors. I am fairly certain I have fuel everywhere now.

One of the three cylinders is trying to fire, the other two not contributing much. If the others kicked in I am sure it would start.

Mike. Remove the bleed screw from the side of the injection pump and crank her over. How far does the fuel shoot out the side of the pump. If 5-6', you have fuel at the injection pump. If it's just spurting out a foot or two, you don't have good fuel flow/pressure at the pump.
 
(quoted from post at 07:58:53 08/22/18)
(quoted from post at 19:09:51 08/21/18)
(quoted from post at 17:21:16 08/21/18) I agree, BTDT many times. You have to remember that while bleeding the lines at the injectors to make sure you hold wide open throttle.


I just went through the sequence again. First at the filter, next at the injector pump, then at the return lines and finally at the injectors. I am fairly certain I have fuel everywhere now.

One of the three cylinders is trying to fire, the other two not contributing much. If the others kicked in I am sure it would start.

Mike. Remove the bleed screw from the side of the injection pump and crank her over. How far does the fuel shoot out the side of the pump. If 5-6', you have fuel at the injection pump. If it's just spurting out a foot or two, you don't have good fuel flow/pressure at the pump.

I only get a dribble. Never have gotten much more. This is gravity feed fuel, no inline fuel pump.
 
I only get a dribble. Never have gotten much more. This is gravity feed fuel, no inline fuel pump.

The CAV injector pump has a "transfer pump" built into the rear end where the line from the filter enters the pump. That is a low pressure high volume pump that should feed the actual injection pump which is a high pressure pump. Look at the description of the parts labelled 14 & 15 in the parts diagram for the pump at the link below:

4500 CAV injection pump parts diagram

If you're only getting a dribble out of the bleed screw hole then either something is blocking the fuel before it gets to the pump, or the transfer pump portion of the pump isn't working properly, or there's something blocking the flow inside the pump itself after the transfer pump section.
 
Isn't the fuel inlet at 58; just to the right of the bleed screw?
There is a fuel line between the fuel filter and 12 on the drawing. This is dry. Should it be an inlet also? It looks like it goes to the dirty side of the filter. Is the filter in 8 on the drawing something I should have replaced?
 
(quoted from post at 20:41:41 08/22/18) Isn't the fuel inlet at 58; just to the right of the bleed screw?

On your pump, No. 58 is probably a fuel line. Look to the left of No. 58 above the serial plate, No. 126. Do you have a small bolt with a 5/16 head. Remove the bolt and energize the starter. Fuel should come shooting out the bleed screw hole "when you're cranking the engine". If you only have a trickle coming out, your pump isn't getting fuel.
 
Always a trickle from the small bleed screw.
When I crack the fuel line to the right of it, I get good (better) flow, so the injector pump is getting fed fuel. Could this be an injector pump issue? Should I have fuel at 12 at any time? I am assuming that is just return fuel when there is excess. The filter in there has not been replaced (#8).
 
I bought a compression tester and it has an injector adapter, but my injectors are much finer threads. Does anyone know where I can find an adapter?
When I took that 1" bold on the top of the injector body loose, I see a spring and pin arrangement. I take that out and crank the engine, no fuel or compression pressure seen in that part of the injector.
How can I get a compression test using an adapter if there is no opening to the cylinder? I also loosened the two bolts on the 'ears' and tried to pull the injector, but it only wiggles. I suspect a big O ring holding it in. There must be a puller for these.

Does this sound right or should I suspect injectors?

Service manual will be here Friday. Sorry if I am asking what I could read then. Just trying to understand the system.
 

I've never taken one of those injectors apart like that but make sure you get all of the parts back in just like they came out.
The two nuts on the ears are what holds the injector in, once you've removed them and the lines use a crows foot bar under the ears to pry the injector up out of the hole.
Carbon on the tip plus a little rust around the body holds them in pretty tight but once it comes loose it'll pop right out.
You'll need a adapter the bolts down just like the injector using the two hold down bolts.
I have 3 adapter so far for my compression gauge, 1 for 65-up Ford tractor engines, 1 for 5.9 Cummins and 1 for 855 Big Cam Cummins.

It's difficult to bleed these engines once they've ran out of fuel, although many are dead set against it I'll use a little starting fluid to get the engine fired off, but it's a little difficult on a 4500 with the air cleaner down in the grill shell.
 

I have tried Starting Fluid, It doesn't seem to help much (more knocking than starting). It used to make the difference.

Where did you get your compression adapter? I really want to get a compression measurement.

Should I get new injectors to replace these? I wonder if I pull one will it go back in without leaking?

Thanks,
Mike
 

Google: S & G 35680
It's a universal adapter like the one from Snap On at half the cost.
Wish I'd known about it before getting mine from Snap On.
 
Sounds like you have just took the top off the injector you need to remove the 2 nuts from the studs on each side of the injector and pry up. Go to the parts page of this site for a picture of the injector.
 
I got the injector out. Used a crow bar and it popped right out.
Got numbers off and ordered an adapter for my compression gage. New injectors and seals ordered. All will be here by Friday.
 
Thanks. This appears to be a TU-15-11A part also. Both seem about the same price and look identical in the picture.
 

Be sure to clean out the hole and make sure the copper sealing washer came out with each injector, any trash in the bottom of the hole won't let the injector seal causing a compression leak.
 
(quoted from post at 06:08:31 08/23/18) Always a trickle from the small bleed screw.
When I crack the fuel line to the right of it, I get good (better) flow, so the injector pump is getting fed fuel. Could this be an injector pump issue? Should I have fuel at 12 at any time? I am assuming that is just return fuel when there is excess. The filter in there has not been replaced (#8).

If we're talking about the same bleed screw, your pump isn't getting fuel. Fuel should be shooting out the side of the pump with the bleed screw removed when you're cranking the engine over. A trickle says to me that your pump isn't getting fuel or isn't making pressure. I'd go with "not enough fuel" first.

What brand of fuel filter(s) are you using. Did you check the tank and determine there was no obstruction at the fuel shut off valve.
 
This is a gravity feed system. What is supposed to pressurize the bleed screw? Is it the injector pump? There is no fuel pump to do it when you crank the engine.
 
I took the injector hidden filter apart and it was caked with rust colored mud. I cleaned it out, put it back and have full flow back at the bleeder valve. I am waiting for UPS (often very late) for the compression tester adapter and new injectors and seals.
 
Something went wrong on my injector filter repair. No fuel at injectors. Pulled injectors again (new ones). Ran compression test. 190, 200, 250 from cab to front (not sure which is 1). I assume that is good for an old diesel and shouldn't be my problem.
I had to disassemble the injection pump port again. I think the spring stack up wasn't right. Now I get the bleed screw to squirt about 6 feet when cranking. Injectors have more fuel at them when bleeding. It almost started twice. One cylinder firing became 2, but it didn't quite make it.
I am going to try the mystery oil in the crank/fuel and pistons while I have the injectors out.
Any other ideas?
 
It Started!!!
Lots of black smoke at first. One cylinder, then two, a little faster, finally running faster than starter. It now idles at 650 with a little lope. 750 fairly smooth. I need to put the valve cover back on and tidy up and try to start it again. Once I shut it off, it did restart easily.
A big part was the injector pump and the filter inside it. I will be ordering a new pump soon since now I remember cleaning the same filter about 20 years ago and putting it back in.
The starting fluid sprayed in the intake and a 10 second pause before cranking seemed to do the trick.
I wonder if it will start easily once it cools back down. It is 60 deg here today so I have hope.
Are 200 psi reasonable compressions for this vintage diesel tractor?
 
Thanks for your help on the injectors and other troubleshooting.
Can I ask one more question? Is 200 psi compression good for my age tractor (1971)? I realize 400 - 500 is new, so I would guess 200 - 250 would still be reasonable.

Thanks!
 
Thanks for your help on the injectors and other troubleshooting.
Can I ask one more question? Is 200 psi compression good for my age tractor (1971)? I realize 400 - 500 is new, so I would guess 200 - 250 would still be reasonable.

Thanks!
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top