One more hard start after sitting, but this one's different

It's progressively getting worse. 7.3 in a 89 F250. Bought it with hard starting problem, that wasn't that bad but suddenly a week ago a lot worse, even though I've been trying to fix the problem. It had 2 bad glow plugs screwing up the controller, so I thought that would be it, but nope. replaced the plugs and it started easier, but I have a 6.9 in a motorhome and that puppy lights up in less than a second of cranking even after sitting a month.
After replacing glow plugs a month ago it would take 10 secs of cranking. Now it suddenly takes twice that, and when it starts a big plume of white smoke.

If I give it a small puff of ether it starts right away. Once it starts it runs like a gem, starts instantly rest of the day. No smoke.

I was convinced it was a glow plug problem so I checked each plug with a meter and they checked ok. I replaced the wire ends with new glow plug connectors and checked for full continuity to each from to controller. 2 new batteries. Decided to bypass the controller with a switch and a heavy duty relay, and now measure almost 11 volts at each plug when cranking. So it's not a glow plug problem.

Starter spins it fast. Starter and battery cables are good.

Decided it has to be a fuel problem - air leak. PO has put a new o-ring kit on injectors with new fuel lines. To test for this, I clamped off both fuel line and return line to keep fuel from draining into tank overnight - no change. I figure if air is getting in, fuel has to be draining, which it's not. Most hard start problems are fuel draining away when sitting but in my example it can't be. Doesn't appear to be leaking anywhere I can see.

The only other thing a bit off on starting is that when my 6.9 starts it immediately runs at fast idle. With this 7.3, although the 2 solenoids turn on, the truck has to run a minute or two before the idle creeps up to fast idle. The 6.9 has a rebuilt IP.
The 7.3 has about 250k kilometres on it. Original IP.

I'm quickly running out of options here, as it seems I've tackled the common sources of start problems and no improvement. Tonight I clamped off the return line to the fuel filter head as I have no idea what else to do, but I doubt that's it - you have to have fuel draining to create the vacuum that lets in air, and I've already eliminated that as a possibility.

Have you messed with your timing at all? Any white smoke when you really get on the pedal driving it?

When you say the high idle takes a minute to kick on, is it chugging and running rough at startup, then smooths out to high idle?

20 seconds of cranking with no smoke visible out of the exhaust shows to me a fuel problem. Whether it's drain back, air intrusion, whatever.

Clamping the lines doesn't necessarily mean it's not draining back. If you're leaking out of one of the olives, especially on the line to the lift pump, you would have problems similar to what you're describing. Remove the fuel filter after it's sat overnight and see how full it is. If it's not plump full of fuel and leaking while you're removing it, you likely have air intrusion somewhere.

Have you installed clear hose on the system yet?

Not sure the year break, but on some 7.3 filter housings, they had a return port on the filter housing that has a check valve in it that likes to leak air back.

No smoke when flooring. Timing hasn't been messed with. When you first start up it starts to fire in one cylinder, and then another and then another and then starts, runs rough for a second or two then smooths out. Just not high idle until I've driven a block or two.
When I'm cranking there is a bit of white exhaust, not much until it starts, then fumigates the whole neighbourhood.

I haven't used the clear fuel line trick yet because my understanding is that if there's air intrusion on the fuel inlet side, the truck will still start normally using the fuel standing in the injection pump and then stall later as the air in the fuel lines/filter works its way forward into the pump. If it won't start at all, it's because air as found its way into the injectors or injector lines because of leakage and air intrusion only on the return line circuit. I clamped the return line shut overnight and didn't make any difference.

I plugged the return line from the fuel filter last night as a last ditch resort but I'm running out of options.

I had this problem, it turned out to be the wiring connections on the glowplugs themselves. If your connectors are like mine, the little white plastic things around the connector crumbled off. So that seemed to aggravate the connection to the glowplug tip. I could unplug and plug back in my glowplugs and it would start fine for a couple of weeks and then do it again.

That's when I went to the manual button. So I could hold the button down and it would start, but sometimes run rough till all the cylinders warmed up. I went and cut the original ends off and crimped some blue bullet connectors you can get at the store and they slid on pretty tight. Seems to work ok now. There is a guy on here that sells a new glowplug harness for these trucks.

Well, clamping off fuel filter return line and nada difference this morning. What's so striking is how easy it starts with just a little **** of ether - a second of cranking to suck it in and she starts right up. If it was air in the injector lines you'd think it would take more than that. I wonder if a cold worn pump has a harder time reaching pop pressure, especially at cranking speed. But once she's fires it's going fast enough to reach minimal pressure.

I wonder if hitting the injector pump with a heat gun and then starting would be a good test?

If it cold starts with a whiff if ether, it's glow plugs..... Air intrusion, with working glow plugs, would be: glow plugs cycle, WTS Goes out, hit the key and it would start almost immediately, run for a few seconds, and die. Then it would be lots of cranking, then fire and run. Even if you had air intrusion and bad plugs, it would start immediately on ether, then die, and crank crank, crank to get it started.....

Start, die, crank , crank, crank, runs and stays running (fairly normal smooth run after the brief purge of air) is air

Crank, crank, crank, crank, starts and runs like s**t, smokes, stumbles and then runs. Or pfft of ether and starts and runs fairly normally, that is glow plugs....

We have one now that at 70+ degrees, it will start and fire without plugs with 7-10 seconds of cranking. It's a bit rough, but will start and run. But get much colder, it wants plugs. Get like it is now... and it want's a couple cycles and cranking...

Rattlenbang said:

The 7.3 has about 250k kilometres on it. Original IP.

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I think that you probably answered your own question here.

Also, change the olives on the hard lines. Probably dry-rotted.

snicklas said:

If it cold starts with a whiff if ether, it's glow plugs..... Air intrusion, with working glow plugs, would be: glow plugs cycle, WTS Goes out, hit the key and it would start almost immediately, run for a few seconds, and die. Then it would be lots of cranking, then fire and run. Even if you had air intrusion and bad plugs, it would start immediately on ether, then die, and crank crank, crank to get it started.....

Start, die, crank , crank, crank, runs and stays running (fairly normal smooth run after the brief purge of air) is air

Crank, crank, crank, crank, starts and runs like s**t, smokes, stumbles and then runs. Or pfft of ether and starts and runs fairly normally, that is glow plugs....

We have one now that at 70+ degrees, it will start and fire without plugs with 7-10 seconds of cranking. It's a bit rough, but will start and run. But get much colder, it wants plugs. Get like it is now... and it want's a couple cycles and cranking...

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My understanding is you can get the problem like mine if you get air in the injectors or injection lines, as the air compresses rather than popping the injectors but the only place for fuel go bleed off is the return line and I blocked that. Air in in the fuel line causes the run and stall as air goes into the injection pump.

And as I said in the above description, each glow plug was tested, I replaced all connector ends, and each glow plug gets just under 11 volts during cranking.

IDIBRONCO said:

I think that you probably answered your own question here.

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I wondered about that, but what exactly can go wrong with a pump where it runs fine otherwise but has a hard time starting cold? Judging by the enormous cloud of smoke when it starts, it is squirting fuel into the cylinder but it's not igniting. Maybe when cold it doesn't have enough pressure to properly atomize the fuel and it's more dribbling out than spraying in a mist?

My guess would be that it's something like that. It could be in your injectors too. That's assuming that they are also the originals with 250,000Km on them. They are at or past the end of their service life. 250,000Km is about 155,000 miles and the normal service life of a pump and injectors is from 100,000 to 150,000 miles. They may still work, but they don't perform as well above the service life.

Rattlenbang said:

My understanding is you can get the problem like mine if you get air in the injectors or injection lines, as the air compresses rather than popping the injectors but the only place for fuel go bleed off is the return line and I blocked that. Air in in the fuel line causes the run and stall as air goes into the injection pump.

And as I said in the above description, each glow plug was tested, I replaced all connector ends, and each glow plug gets just under 11 volts during cranking.

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You ohmed them.... that doesn’t mean they are good. I had a set that ohmed ok, and the truck wouldn’t start. replaced all 8 plugs and it fired right up. Just because you are getting voltage to the connector on the plug, doesn’t mean the plug is good or heating. The only way I would call a plug good is to remove it, hook it to a battery and see if it gets “NASA Hot” quickly..... if not.... then it’s dead.

Also, if you have air intrusion, the hard lines to the injectors, and the injectors themselves don’t empty. It is the supply to the filter, and normally the filter that drains back. I don’t think the pump normally drains out (That would best be answered by Wes or Russ). This is why it will start and run, then die. It uses the fuel still in the pump and lines, and then runs out because the filter is still trying to refill.... what you are describing about the air in the injection lines is after a pump to injector replacement, not running out of fuel....

I would order a set of plugs, put them in and see how it goes. Everything that you are describing, to me, says plugs. The it will start fine cold with ether, but not the plugs say plugs, not air....

snicklas said:

You ohmed them.... that doesn’t mean they are good. I had a set that ohmed ok, and the truck wouldn’t start. replaced all 8 plugs and it fired right up. Just because you are getting voltage to the connector on the plug, doesn’t mean the plug is good or heating. The only way I would call a plug good is to remove it, hook it to a battery and see if it gets “NASA Hot” quickly..... if not.... then it’s dead.

I would order a set of plugs, put them in and see how it goes. Everything that you are describing, to me, says plugs. The it will start fine cold with ether, but not the plugs say plugs, not air....

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That's such a strange issue - ohm ok but still don't fire? I thought they either worked or burned out. I'll check each out across a battery - I'm not big on throwing parts at a problem to see what fixes it, not when there are other options.


And while I realize that pump and injectors are long in the tooth, since it runs so well once it's going it's not my first go-to for solving this. given it's close to $1000 to replace everything.

Original IP with 250K on it, boy you got your $ out of that one! They don’t usually make it that long.

If the starter spins fast, and the engine kicks over on ether, I’d be looking at that IP. Get a flashlight, look underneath it for signs of fuel leaking onto the valley pan.

Have a professional diesel shop check the pump out if you’re unsure. Just replaced the 30 year old IP on my truck and put a matching set of injectors in the truck. All Stanadyne parts. Cost about $1200 all in, but boy did it WAKE THAT TRUCK UP! No more hard starting either.


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