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 Rebuilt 1988 7.3 hard to start. (Fixed)
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maxx62
Senior Member

United States
106 Posts

Posted - 11/03/2008 :  4:33:45 PM  Show Profile  Reply with Quote
I have a 7.3 that I inhereted and finished putting together and when starting the bus for the first time it was hard to fire because of the air and bad starter. After replacing starter and bleeding fuel system got the bus started,runs good no miss,problem is after it has sat overnight or a couple of days you have to crank it several tries
to start and smokes alot blue/gray raw fuel. The engine fires right up after you get it started and runs a minute. My question is would bad injectors cause this if they were not popping at the right pressure. The bus has about 190,000 miles which I think are orignal injectors. Thanks, sorry for the long question.

Edited by - maxx62 on 11/10/2008 4:56:21 PM

International-9.0
Advanced Member

USA
394 Posts

Posted - 11/03/2008 :  5:57:39 PM  Show Profile  Send International-9.0 an AOL message  Reply with Quote
If it only runs real rough when cold, I might suspect glow plug issues of some sort. Could be plugs, controller or any kind of wiring problem in the system. Don't go out and buy a set of plugs without first troubleshooting the system. If they aren't work, starting will be very hard and it will smoke excessively until warmed up. If the system is working correctly, even after the vehicle starts, the plugs continue to cycle (pulse on and off to keep them from overheating). This helps reduce smoke when warming up as well as helping the engine to run smoother.

You might test your fuel pressure at the vane lift pump that is located on the end of the hydraulic head. On a 6.9 which uses the same pump (DB2), the pressure at the hydraulic head should be between 95 and 110 psi. It's possible these aren't the correct pressures for the 7.3, but I'd imagine they are close. Anybody have a 7.3 diagnostic manual? Usually low fuel pressure would cause problems all the time, not just starting. I'd check glow plug system first. I hope this helps.

Jonathan
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contactbluebird
Senior Member

USA
81 Posts

Posted - 11/04/2008 :  12:42:51 PM  Show Profile  Visit contactbluebird's Homepage  Click to see contactbluebird's MSN Messenger address  Reply with Quote
We have a 1993 7.3 that's hard to start as well. Once it starts, it runs fine and restarts fine. But when it sits over night you will have to wind on it alot before it will start. Lift pump? Injection pump?
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bbird66
Top Member

USA
881 Posts

Posted - 11/04/2008 :  8:26:42 PM  Show Profile  Reply with Quote
Check the obvious, glow plugs, and check the resistance of each one and make sure power is coming out of the coil to the plugs. If you need to replace one or more...be very careful to NOT twist those off! Or you (maybe) will be using lots of bad words..

Were gonna miss you "Brent"..Good luck in "Heidi land"

"I know you miss the Wainwrights Bobby, but they were weak and stupid people...and that's why we have wolves and other large predators" .. The Far Side

"On a two hour delay when will my child be picked up??"








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Bassman
Top Member

USA
510 Posts

Posted - 11/05/2008 :  04:43:54 AM  Show Profile  Reply with Quote
A leak in the O-rings that seal the plastic caps on the injectors or one of the little return hoses can cause this also. When there is a leak anywhere in the return circuit, fuel leaks down overnight allowing air to build in the system which can make it hard to start after sitting.
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wagonmaster
Top Member

USA
2298 Posts

Posted - 11/05/2008 :  05:17:07 AM  Show Profile  Reply with Quote
We had a huge fleet of 6.9/7.3 engines at one time and even in our warm climate glow plugs and glow plug controllers were almost always at the heart of hard starting cold engines. Absolutely check there first.

Joe
Land of the Free, because of the Brave!
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Aint Skeered Racing
Senior Member

United States
68 Posts

Posted - 11/05/2008 :  5:57:50 PM  Show Profile  Visit Aint Skeered Racing's Homepage  Send Aint Skeered Racing an AOL message  Send Aint Skeered Racing a Yahoo! Message  Reply with Quote
Well what I do is soak rag in gas and cover up the air filter so it'll suck in the fumes and it'll start right up but its not like im cranking it over for awhile I just use the rag right away so I won't put wear and tear on starter any more than I have to but I don't know if that'll hurt the motor or not

Jimmy Volk #76
Aint Skeered Racing
School bus racing asphalt Figure 8s and oval dirt racing

Owner of 26 racing buses
14 buses destroyed
12 buses running
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International-9.0
Advanced Member

USA
394 Posts

Posted - 11/05/2008 :  6:09:46 PM  Show Profile  Send International-9.0 an AOL message  Reply with Quote
That is about the same thing as spraying ether in there. As long as you limit the amount of ether, you are usually ok. In time though, I've seen engines that were damaged by ether and it was ugly. It's a good occasionaly but I wouldn't use it as a permanent solution. The biggest reason NOT to do it is the glow plugs. In the event some are working, you could cause an explosion. Be careful with the fumes, same thing...

Jonathan
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ModMech
Top Member

USA
948 Posts

Posted - 11/07/2008 :  09:41:31 AM  Show Profile  Visit ModMech's Homepage  Reply with Quote
All the IDI engines (6.2L/6.5L/6.9L/7.3L) will BREAK the pistons on ether or any other "starting aid", gasoline included. The pistons are NOT strong enough to take the BANG! of that type of fuel igniting (exploding) in the combustion chamber, Glow Plugs or not.

The fact that it starts ok AFTER the first start of the day indicates either the lift pump (side of the engine below alternator) is not working or the fuel is draining down from leaking injector bleed-off caps or their hoses.

You DO NOT have an injector problem, if you did, it would misfire badly all the time.

If you want customer service, you NEED an International!
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International-9.0
Advanced Member

USA
394 Posts

Posted - 11/07/2008 :  5:41:35 PM  Show Profile  Send International-9.0 an AOL message  Reply with Quote
I saw an engine that had all the edges of the pistons broken off. One piston in particular had the one huge chunk out of the top side broken off from somebody spraying an excessive amount of ether in there. This was on a gas engine with a bad fuel pump and this was their way of getting it started every time until the pump would fill the carb back up.

In general, it's not a good idea. I think it's acceptable in a "pinch" if you are careful about how much you put in and that you do not spray until the engine is turning over.
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maxx62
Senior Member

United States
106 Posts

Posted - 11/08/2008 :  6:03:08 PM  Show Profile  Reply with Quote
Problem solved,Installed the new glowplugs and bus fired right up. Thanks for your replies.
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misterbill
Advanced Member

United States
303 Posts

Posted - 11/23/2008 :  09:18:59 AM  Show Profile  Reply with Quote
My 7.3 will not start without ether. Been starting it that way for several years. Also-I have to crank it for 30 seconds or it will start and cut out, then it will not start at all. It started smoking terribly last spring, I took it to a friend who runs a truck repair facility. He told me that the Ford injector pumps have to mantain pressure to work, when they get old they leak pressure and won't start. I am trying to come up with $600 to replace the pump and injectors. I am afraid to put new glow plugs in because I really don't want it to start before I crank it for 30 seconds. The person that I buy starters from loves me.

High School Friend-"Hey! How are you! Well, I guess you can't be doing too well, you're driving a school bus."
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International-9.0
Advanced Member

USA
394 Posts

Posted - 11/23/2008 :  3:53:13 PM  Show Profile  Send International-9.0 an AOL message  Reply with Quote
You need to put a gauge on the hydraulic head and see what the transfer pump pressure is. There's a lift pump on the side of the block that brings fuel form the tank, and the injection pump has a built in transfer pump. See if you have correct pressure at the head. I don't have the specs for the 7.3, but if you are somewhere around 100, you are most likely ok. I'd check this before throwing a new pump at the engine. If you plan to fix the vehicle, do repair the glow plug system. Keep in mind it could be the controller or wiring, and not the plugs themselves. If you have good pressure at the hydraulic head on the pump, and you are sure the whole glow plug system works correctly, let us know. If you have not done so, might not hurt to change your fuel filters. Also make sure you have noe air leaks between the block mounted lift pump and the tank. Might not hurt to check the leakoff lines for leaks too. The fuel may be draining back into the tank and that is what takes so long for the engine to start. You are having to reprime the system. See what you can find....Good luck!

Jonathan
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