Author Topic: diesel trouble starting  (Read 3748 times)

Offline Jimo

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diesel trouble starting
« on: June 28, 2017, 08:11:29 PM »
I have a 1985 6.2 liter diesel that when I start it, if I do not hold  it  at a high RPM and it cuts off, it will not restart. I have to leave it for a few  hours and try again which sometimes runs the batteries down-it has had new batteries in the last year. Any suggestions on what is the problem?
Thanks,
Jimo
« Last Edit: June 28, 2017, 09:14:34 PM by Jimo »

Offline fitz

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Re: diesel trouble starting
« Reply #1 on: June 28, 2017, 10:42:12 PM »
Is this by any chance a Military CUCV?
It sounds like you may have air in the fuel lines.
This can happen as the rubber fuel lines get old and air leaks in.
On the Military trucks there is a fuel sensor on the base of the fuel filter base ( the civilian trucks don't have this sensor). The O ring on the sensor can crack over time and let in air.
One way Way to check for air leaks is to replace the rubber fuel line that goes from the check ball on the injector pump to the steal return line with a clear line.  The line is only a few inches long (I can get a picture of the line I'm talking about if you need 1).
With the clear line in place, let the truck idle and look for bubbles in the fuel. If you see bubbles, you have air leaking in.  Keep in mind the clear line you find at the hardware store is probably not rated for fuel use, so just put it on for the air bubbles test.  I wouldn't drive the truck with the clear line on it.
If you see bubbles in the fuel, air is leaking in and causing your hard start / stallig issue.

Offline Irish_Alley

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Re: diesel trouble starting
« Reply #2 on: June 29, 2017, 07:13:35 AM »
im with fitz about air, keep in mind you may not see any fuel leaking but it can still suck air. you also have the rubber lines up by the fuel tanks that could be your problem

the clear fuel hose is a trick i keep hearing about. but never have i seen someone suggest to remove it after "testing". it makes sense to remove it, but there might be a hose thata rated for diesel.
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Offline Irish_Alley

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Re: diesel trouble starting
« Reply #3 on: June 29, 2017, 07:28:44 AM »
im only seeing 1/4" or so on ebay for clear/ish diesel fuel line
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Offline Jimo

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Re: diesel trouble starting
« Reply #4 on: June 29, 2017, 08:20:28 AM »
Fitz .and Irish Alley,
 It is a 1985 Chevy Silverado. I bled the fuel filter that is mounted on the firewall and other than the initial air bubbles clearing out the bleed line, it does not have air in it. Also as info when I fill it up, it has air pressure in the tank that escapes as I remove the fuel cap.

It starts very well, and if I keep the rpms at about 2000, for about 10 seconds it will continue to run. If I let the rpms drop and it cuts off, and try to restart, it runs the battery down.   After it is warm it will start immediately with no problem.

Thanks for the suggestions.

Jimo

Offline Irish_Alley

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Re: diesel trouble starting
« Reply #5 on: June 29, 2017, 08:41:47 AM »
Procedure 4. Checking for Air Leaks
If stalling or rough operation only occurs after cold startup, check for fuel leaking backwards or air leaking into the
fuel supply lines. Fuel leaking backwards may be caused by faulty check valves in supply pump.
To check for this
condition, remove return line connector fitting (ball check) from the top of pump and install a plain fitting in its
place. Connect a section of clear hose approximately 3 feet long to the fitting and route to a container. Start engine
and allow to idle. Stop engine. Suspend clear hose from hood of vehicle and mark fuel level in hose.
Quote
ó NOTE ó
Allow sufficient room in hose for level of fuel to rise due to thermal expansion. If level
drops over a period of several hours (or sooner), a leak back condition is indicated.
Occasionally a very small air leak will only let enough air into the system to cause a stalling problem or rough
running condition after the vehicle is shut down for many hours (such as overnight). Double check all fittings,
clamps and fuel lines and do not overlook components after the supply pump such as the fuel filter element or
base. There have been cases where tiny holes in the filter base casting or in the sealant used in the manufacture of
the filter element have allowed air to enter but no external fuel leakage to occur.

Air Leak Diagnosis
AIR LEAK ON THE SUCTION SIDE
The housing vent wire may allow minute quantities of air to pass harmlessly out of the pump. However, at some
point there w ill be more air than can go out the vent and the air will go into the charging circuit. This air will
compress and upset fuel flow in the lines which will create a rough running engine. A plastic line placed on the
fuel return fitting will show up this condition. To isolate the air leak, it may be necessary to feed the system out of
a container and hook it up at various places to bypass certain sections of the fuel system.

AIR LEAK ON SUCTION OR RETURN SIDE
An air leak in either the suction or return side can cause starting problems. Air entering the system will allow fuel
to drain back towards the tank. If an air leak occurring at some point like the filter, the fuel will drain back then the
fuel on the return side will be heavier and it will pull fuel out of the filter through the pump and back towards the
tank. Because there is no fuel in the filter or pump, the engine will not start. When it finally does, surging will be
very evident.
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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Irish_Alley

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Re: diesel trouble starting
« Reply #6 on: June 29, 2017, 08:47:55 AM »
heres the 6.2 manual. i wouldnt print it out unless you want to print 386 pages
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Training/GM_STG_16015_05_1C_1987_The_6_2_Liter_Diesel_Engine.pdf

this link will take you directly to the page i took that info from. it and the page below (377) are the only ones that mention cold stalling, which is what youre describing
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Training/GM_STG_16015_05_1C_1987_The_6_2_Liter_Diesel_Engine.pdf#page=376
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline bd

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Re: diesel trouble starting
« Reply #7 on: June 29, 2017, 09:02:47 AM »
To supplement your diagnosis for air entry, when you remove the return fitting from the top of the pump, look through the fitting while holding it to a bright light.  The integral check ball is made from translucent glass.  If there is any debris trapped around the check ball seat or if the check ball is shattered, it should be evident.  Debris indicates that the elastomer ring inside the pump is disintegrating, which calls for pump repair.  Make sure the o-ring that seals the fitting is undamaged.  You should also check the cold advance solenoid operation.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Jimo

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Re: diesel trouble starting
« Reply #8 on: June 29, 2017, 10:24:57 AM »
Irish Alley and bd, THANKS for all the great advice and the diesel manual.
As an update, I did get it started. Maybe not the best way, but I poured several ounces of fuel into the intake.  It started and smoked aplenty for about two minutes and then smoothed out. I shut it off and it cranked back up quickly. It seems that obviously it was not getting fuel. The first thing I plan to do is to change the fuel filter and check the hoses. It is my main vehicle and I plan to keep it forever, so the advice from all respondents and the manual are much appreciated.

Jimo
.


Offline Irish_Alley

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Re: diesel trouble starting
« Reply #9 on: June 29, 2017, 11:06:55 AM »
from what youre describing i would almost think fuel is slowly draining back to the tank. and i would pretty much bet its from that check ball
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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Jimo

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Re: diesel trouble starting
« Reply #10 on: June 29, 2017, 11:41:53 AM »
Irish Alley, I agree. I will probably just go ahead and change the pump.

Jimo

Offline bd

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Re: diesel trouble starting
« Reply #11 on: June 29, 2017, 11:54:50 AM »
Injection pumps aren't cheap!  It would behoove you to narrow down the cause before throwing parts (money) at it.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Irish_Alley

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Re: diesel trouble starting
« Reply #12 on: June 29, 2017, 12:39:26 PM »
i just got done getting my ve pump rebuilt, cost about 500. i tried to do it myself but i wasnt sure i did it right and i think i didnt get the timing right so i had to send it off.


but if the ball is the issue you should be able to replace just that
« Last Edit: June 29, 2017, 12:40:59 PM by Irish_Alley »
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Jimo

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Re: diesel trouble starting
« Reply #13 on: June 29, 2017, 01:30:23 PM »
The pump I was referring to being changed was the mechanical pump on the side of the motor. They are not very expensive. Other than the occational problem of not starting well, it does great. But I will also check the injection pump.

Jimo


Offline Irish_Alley

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Re: diesel trouble starting
« Reply #14 on: June 29, 2017, 01:44:44 PM »
oh ok. i swapped the 350 from my 91 to a 12v. kept the pumps in the tanks, works better imo cause now i dont have to hand pump anything just have iol pressure and the pump turns on
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes