1989 7.3 IDI - hard starting & hitting a brick wall

NWArcade

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I have a 1989 F250 7.3 IDI that I’ve owned for about 10 years and it has never started as it should. I am mechanically inclined and do all the work to my truck myself. This said, I’m at the point where I’m pulling my hair out trying to solve the hard starts.

Here is what I know and what I've done so far:
  • Read as many relevant 7.3 IDI hard start posts, as humanly possible:)
  • The injectors are original, with the grey engine paint clearly visible on them. They could have been rebuilt, but I will assume they are original and un-serviced.
  • I am uncertain of the age of the injector pump, but by the looks of it, it is not original.
  • I’ve replaced all the fuel return lines, caps, o rings, etc.
  • The glow plugs are newer and are motorcraft. They all test out around .2 - .3 ohms
  • The glow plug controller is newer and is a motorcraft. I’ve tested the power in and outgoing and all are within spec.
  • The glow plug wiring harness is new. The glow plug circuit operates as designed and within spec.
  • The qty 2 / 10 gauge wires at the passenger fender have been cut out of the melted harness and properly spliced. They are both putting out power to the relay, as designed.
  • The lift pump was replaced with an electric pump. It is a facet 4022N. The hard-line for fuel feed to the electric pump was replaced along with the feed line from the electric pump to the head. The hard-line remains from the output on the filter head to the injection pump (with no leaks that are visible to the naked eye).
  • Arriving at the truck in the morning if I turn the key on the electric fuel pump runs and when I check the Shrader valve on the filter head fuel comes out immediately, with zero air.
  • I’ve checked for wet spots all the way back to the tank. The valley of the truck is dry as well. No apparent leaks of any kind remain.
  • If a cold start, the glow plugs run for about 15-20 seconds and once cranked it will start after about 20 seconds of cranking or sometimes 2 tries. Never less. The truck pointed/parked up or down does not affect it, for better or worse. Both tanks work and I’ve tried parking pointed up/down with different tanks, no change.
  • As soon as it starts, it does blow out some unburnt diesel, but nothing major though.
  • The hard start issue from dead cold is present when it's 80 degrees out and if it's 20 degrees out.
  • The engine runs smoothly as soon as it starts and never stalls.
  • Starting with half or full throttle (per the dash visor instruction) does not seem to help. It seems to start better with no throttle after the high idle is set.
  • Once the truck is turned off (after a cold start) and immediately restarted it will start within about 3-4 seconds.
  • If warmed up, high idle off, and the truck is then turned off it will start within about 1 second.
  • If plugged in for a few hours, it will start within about 1 second.
  • Doing multiple cycles of the glow plugs doesn't really help.
  • The batteries are newer and are 850 CCA
  • The starter is a DB electric, gear reduction. The truck spins plenty fast enough.
  • Battery cables are original, but not so sure doing so would help much.
  • At the filter head, the one-way check valve was bad and has been replaced with a spliced-in with a new one-way valve in the correct orientation.
From everything that I’ve read, everyone says that this condition is caused by a glow plug issue. This said, I’ve tested everything thoroughly and can say with confidence that my glow plug system is working as designed. I don’t seem to have a drain back issue at the filter head. I guess it’s possible that one or more of the injectors are leaking and causing a drain into the cylinder(s)? Or could it be a failing injector pump or a combination of failing injectors and a failing pump? I’d hate to invest in all new injectors and an injection pump and then find out that was not the issue. Any advice on what may be causing this issue or creative ideas on how to test/rule things out? I love this truck, but have hit a brick wall on what to do to solve its hard start issue once and for all. Thank you in advance for your thoughts and any assistance you can offer.
 

Rdnck84_03

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Ok that was alot to read through. If I missed where you mentioned this I'm sorry. Have you tried putting a test light on the actual glow plug connector to make sure power is actually getting to them?

James
 

NWArcade

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Ok that was alot to read through. If I missed where you mentioned this I'm sorry. Have you tried putting a test light on the actual glow plug connector to make sure power is actually getting to them?

James
Apologies for the long explanation. No problem, you didn't miss anything. I've never tested each individually, only the input power and output at the lugs on the controller. I just went out and did some testing. While the glow plugs are under load and all of them are being powered, they all test (individually) at 9.66 volts at the glow plug (while hooked up and powered by the harness).
 

Rdnck84_03

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Here is the proper tests to do with the 7.3L IDI glow plug system. First, use a test light on all your glow plugs to verify they are good. Then, reconnect your plugs, and when you connect the #2 cylinder glow plug, trap a single strand of fine wire under the cap, so that you can use it as a test point. Put your postive of your meter test lead on the single strand of wire, and your other probe to ground. Set your meter to 12 volts. On a cold engine, you should see 6 volts at the #2 cylinder glow plug. The voltage will slowly rise as the plugs heat until you get to around 11 volts at which time the controller will cut the voltage and your wait to start light goes out. IF your voltage is higher than 6 volts starting out, then some of your glow plugs are failing, or you have bad connections in the wiring. If your voltage is less than 6 volts, then you have voltage supply issues. Check the following. Put your positive voltmeter probe on the large lug on the GPC that is fed from the battery. Put your negative probe on the Z strip lug. You should see battery voltage at this point. Have an assistant turn on the key, and verify that your voltage drops to near zero. If it has over half a volt, then your contactor is worn. If this test passes, put your positive probe on the positive post of your battery, and the negative on your large GPC lug coming from the battery and measure for voltage loss there.
This gives a detailed description of how to test the glow plug system.

James
 

catbird7

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I agree it sounds like a glow plug issue, or at least given the info provided that's where I'd start. The fact it starts without issue when it's plugged in, reinforces the notion it's a glow plug or glow plug wiring issue. Possibly pull one of the plugs, reattach the wire, then turn the key and see if the plug gets hot??? I'm a poor source for wiring problems however the "fire right up after being plugged in" statement jumped out at me. I'm not certain what the voltage reading should be at the connection to glow plug, possibly 9.66 volts is normal however i would've expected it to be the same as the reading at the battery??? Others that are more knowledgeable regarding this should chime in. I also have an 89 Brick, and seem to remember this was a transition year where the 6.9 engine was still available {feel free to correct me on this if I'm wrong}, therefore is it possible your truck was originally supplied with 6.9 and now has a 7.3 with 6.9 glow plug wiring? Just some things to think about.
 

NWArcade

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This gives a detailed description of how to test the glow plug system.

James
Here are my results. Thoughts? Both the glow plugs and controller have less than 500 miles on them. Both are motorcraft. Glow plugs ohm out at around .2 and .3 and burn bright red with 12 volts applied. Glow plug harness is new as well.

Put your postive of your meter test lead on the single strand of wire, and your other probe to ground. Set your meter to 12 volts. On a cold engine, you should see 6 volts at the #2 cylinder glow plug. The voltage will slowly rise as the plugs heat until you get to around 11 volts at which time the controller will cut the voltage and your wait to start light goes out. IF your voltage is higher than 6 volts starting out, then some of your glow plugs are failing, or you have bad connections in the wiring. If your voltage is less than 6 volts, then you have voltage supply issues.

***VOLTAGE IS 9.66 AND DOES NOT CHANGE UNTIL THE 20-SECOND MARK AND THEN IT CYCLES AND TURNS OFF.***

Check the following. Put your positive voltmeter probe on the large lug on the GPC that is fed from the battery. Put your negative probe on the Z strip lug. You should see battery voltage at this point.

***12.50 VOLTS***

Have an assistant turn on the key, and verify that your voltage drops to near zero. If it has over half a volt, then your contactor is worn.

***.20 VOLTS***

If this test passes, put your positive probe on the positive post of your battery, and the negative on your large GPC lug coming from the battery and measure for voltage loss there.

***12.20 VOLTS***
 

NWArcade

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I agree it sounds like a glow plug issue, or at least given the info provided that's where I'd start. The fact it starts without issue when it's plugged in, reinforces the notion it's a glow plug or glow plug wiring issue. Possibly pull one of the plugs, reattach the wire, then turn the key and see if the plug gets hot??? I'm a poor source for wiring problems however the "fire right up after being plugged in" statement jumped out at me. I'm not certain what the voltage reading should be at the connection to glow plug, possibly 9.66 volts is normal however i would've expected it to be the same as the reading at the battery??? Others that are more knowledgeable regarding this should chime in. I also have an 89 Brick, and seem to remember this was a transition year where the 6.9 engine was still available {feel free to correct me on this if I'm wrong}, therefore is it possible your truck was originally supplied with 6.9 and now has a 7.3 with 6.9 glow plug wiring? Just some things to think about.
Agree with you, it would seem logical that my glow plug system has an issue. All glow plugs glow red hot when hooked up to 12 volts and they, along with he GPC are basically new.
 

Rdnck84_03

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Here are my results. Thoughts?
I will be completely honest, I am completely unfamiliar with the factory system. I have yet to play with the 7.3 controller setup. Both of mine are 6.9 and setup on manual control.

Hopefully someone else knows what could cause whatever you have going on.

James
 

NWArcade

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I will be completely honest, I am completely unfamiliar with the factory system. I have yet to play with the 7.3 controller setup. Both of mine are 6.9 and setup on manual control.

Hopefully someone else knows what could cause whatever you have going on.

James
James - thank you. Hopefully, I can get it worked out before it gets really cold out;) Happy Thanksgiving to all!
 

MadMac

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This sounds like the problems on my ‘85 6.9, which is a somewhat different animal. I also chased GP/electrical for a long time, but mine turned out to be the fuel separator, which was rectified by a bolt on racor unit. I don’t disagree about the GPs being the right target, but your description about how it happens no matter what after partially cooling - doesn’t strike me as GPs.

Along my similar journey I replaced the controller, relays, GP harness, GPs, return lines, lift pump, senders - everything GP related essentially. Measured voltages and current, suspected 25 year old aluminum wiring as a problem (it was - but marginally). Replaced the batteries with a pair of red tops, which helped but did not solve things, but made me very aware of how easy it is to burn up the stock diesel rated starter, not once but twice (yes the upper bolt requires a swivel socket, two diff extension lengths, and a 100% blind two handed methodology).

Engine block heating marginally helped, but once it sat for 4 hours - even in the heat, it was the same thing 20 to 30 seconds of cranking. No observable fluid leaks. The best of all the replacements (which really didn’t work) was a new 4-0 copper wiring battery to starter harness - but the benefit was limited to “stability of symptoms”. Still stumped - clear tube tested all the fuel lines which were fine (but not post IP…). Still took 20 to 30 cranking seconds to get the first sputter.

In a “can’t hurt” middle of the night moment online, I ordered the Racor unit and then replaced the stock separator - and have never had a single starting problem since. If it sits for 3 months in a dead cold wet winter (cold to me - no snow…), 18 times out of 20 - instant starts. 1 in 20 it starts in the first 2 seconds at half throttle after two six second GP cycles. The other 1 in 20 - starts within 5 seconds. Most reliable starting of all my other gassers and diesels. Note: I still aspire to be a decent wrench, which I’m not…
 

NWArcade

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This sounds like the problems on my ‘85 6.9, which is a somewhat different animal. I also chased GP/electrical for a long time, but mine turned out to be the fuel separator, which was rectified by a bolt on racor unit. I don’t disagree about the GPs being the right target, but your description about how it happens no matter what after partially cooling - doesn’t strike me as GPs.

Along my similar journey I replaced the controller, relays, GP harness, GPs, return lines, lift pump, senders - everything GP related essentially. Measured voltages and current, suspected 25 year old aluminum wiring as a problem (it was - but marginally). Replaced the batteries with a pair of red tops, which helped but did not solve things, but made me very aware of how easy it is to burn up the stock diesel rated starter, not once but twice (yes the upper bolt requires a swivel socket, two diff extension lengths, and a 100% blind two handed methodology).

Engine block heating marginally helped, but once it sat for 4 hours - even in the heat, it was the same thing 20 to 30 seconds of cranking. No observable fluid leaks. The best of all the replacements (which really didn’t work) was a new 4-0 copper wiring battery to starter harness - but the benefit was limited to “stability of symptoms”. Still stumped - clear tube tested all the fuel lines which were fine (but not post IP…). Still took 20 to 30 cranking seconds to get the first sputter.

In a “can’t hurt” middle of the night moment online, I ordered the Racor unit and then replaced the stock separator - and have never had a single starting problem since. If it sits for 3 months in a dead cold wet winter (cold to me - no snow…), 18 times out of 20 - instant starts. 1 in 20 it starts in the first 2 seconds at half throttle after two six second GP cycles. The other 1 in 20 - starts within 5 seconds. Most reliable starting of all my other gassers and diesels. Note: I still aspire to be a decent wrench, which I’m not…
Yeah, I agree, my issue is a bit of a head-scratcher for sure. I can empathize with all the work that you put into your rig to get it to reliably start. I bet that was very satisfying once you got it all dialed in!
 

Cant Write

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I’m stuck on your 9.66v test when Agnem states it should be 6v, and if over....bad connections or failing GP’s

They all test .2-.3 ohms when cold, and all “test” light up, but could they be failing when hot? Does the controller “click” at all?

How many miles on the pickup? Have you ever done a compression test? Would low compression in one or more cylinders coupled with a cold engine cause these symptoms? And by cold I mean the combustion chamber, not the outside temp.

If you disable the GP system. Spray the air filter with ether, does it fire right off on a cold start?

I’m pulling at straws. After ten years of ownership, don’t give up yet!!!
 

Rdnck84_03

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How many miles on the pickup? Have you ever done a compression test? Would low compression in one or more cylinders coupled with a cold engine cause these symptoms? And by cold I mean the combustion chamber, not the outside temp
I was thinking the same thing pretty early on here. I was waiting until all the glow plug options were exhausted before I recommended the compression check.

I'm just not really understanding why the voltage is not checking out on the one test when everything else seems to check out correctly.

James
 

Rdnck84_03

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Just a crazy thought, is it possible some of the glow plugs are for some reason not grounding good in the heads?

That would show up to the controller as bad plugs, and also be functional when removed and tested.

James
 

MadMac

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Just a crazy thought, is it possible some of the glow plugs are for some reason not grounding good in the heads?

That would show up to the controller as bad plugs, and also be functional when removed and tested.
I was starting to think down this line, but differently, the age & mileage may be an indicator… of how much other work has been done which you may not be aware of. IFF 6v is what is expected, there are only two ways I can think of (again, I’m not a good-wrench !!!) is 1) some bad wiring was injected previously / there is a bad “leaking” connector, 2) the new controller or something else new in the chain is bad.

Maybe you have the 1 in 1000 electrical part which was marginal enough to make it out of the factory… and broke the first time. The act of testing electrical things, can sometimes lead to unintended consequences… says the now firm believer in anti-static bags and “known good cables”. None of these are easy things to track down. Might be time to find and compare to the electrical wiring diagrams for your truck….
 

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