Larry Turner via Mercedes <mailto:mercedes@okiebenz.com>
January 2, 2017 at 7:27 AM
Hey Curley, This is a very definitive troubleshooting guide. It's a
keeper.
What do you think about me testing my old GPs with a old Battery?
Actually I have 3 old 12v batteries not being used so any of them
could be used. My biggest concern is this test would make a GP glow
red indicating (to me at least) the GP is good. Is that a false
assumption?
Thanks!
Larry
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Curley McLain <mailto:126die...@gmail.com>
December 26, 2016 at 9:21 AM
Basics:
0. put the charger on the battery to recharge/maintain it during a
lot of cranking.
1. Crack the fuel line(s) then crank to make sure you have fuel
delivery. About 720º degrees rotation on the crank should be
enough. If you need to bleed the system, more cranking is needed.
2. If fuel is being delivered to the nozzles, Then proceed to
electrical checks
3. Key on to glow position, check for 12V at each GP. Be careful
not to short the probe to ground. You may need a couple of glow
cycles to complete this. A helper to turn the key to glow/off makes
it easier.
4. Pull off the cover from the GP relay, pull the plug to the GPs.
If 0V on step 3, turn key go to glow and check for 12V on the relay
at the terminals for the GP wires. If 0V, replace fuses first, if
present. Otherwise, replace GP relay.
(a further test is possible to make sure the key is delivering juice
to the relay to turn on the relay. Consult wiring diagram for this
info) If a fuse is present, it is generally a fuse problem. if a
new fuse does not fix it, and GP, GP wires are good, it is almost
always a bad relay.
5. If all used relay pins are delivering 12V to the wiring harness
to the GPs, turn the multimeter to the lowest ohm reading you have.
check meter for zero. If you can't get 0, offet your reading by the
static amount. Check the used sockets in the plug on the GP harness
between one socket and ground. Book value is 1.4 ohms. 0 ohms is a
open plug, replace it. over 1.7 ohms os a bad plug, replace it, if
you are sure your meter is reading correctly. It takes a good meter
to read 1.4 ohms. with a cheap ($10 HF) meter it is 0 or infinity,
so if you get something near 0 ohms, you assume it is good; infinity
indicates it is an open circuit, replace the plug. GPs usually fail
open. A GP with say 2.4 ohms reading is on its way out and needs to
be replaced. 2.4 is about as high as I have seen. I have seen
meters that consistently read 1.7 on good or new GPs, so you have to
learn your meter's idiosyncrasies, unless you have a very expensive
($500+) meter.
You guys edit this to make this an all purpose troubleshooting
formula for non start or slow start Diesels.
Larry Turner via Mercedes <mailto:mercedes@okiebenz.com>
December 26, 2016 at 8:42 AM
No. i probably didn't explain the chronology very well.
1,. Tried to start it - had to crank excessively to get it to finally
start - .
2. After excessive cranking it started running very rough - exactly
like it would be when 1 or 2 GPs go dead.. (After your question
about the dash light I recalled it being illuminated while the car
was running.)
3. During this start up episode I noticed lots of white smoke from
the exhaust pipe.
4 Since I had 5 new GPs on the shelf I jumped in to R&Ring the GP
probably too quickly.
5 After replacing the GPs I tried to start it and it just cranked
over. Since I had removed the fuel lines to get access to the GPs,
I failed to bleed them after re-installation.
6 My next step will be to bleed the air from the fuel lines then try
to start it once more.
7. I will do the electrical tests suggested by Mitch to confirm my
relay has died. BTW, I checked the in line fuse just in case only to
find it perfect. I think there's a fuse across the bottom of the
relay but doubt it has gone bad.
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Larry Turner via Mercedes <mailto:mercedes@okiebenz.com>
December 25, 2016 at 7:45 PM
That's a great idea! I remove the intake manifold when replacing GPs
and forgot I need extra cranking to get rid of the air in the fuel
lines. I R&R'd. Can't believe I forgot spmething so basic!
Thx agn!
LarryT
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Fred Moir via Mercedes <mailto:mercedes@okiebenz.com>
December 25, 2016 at 7:31 PM
LarryT.
Air leak? Letting the fuel drain back into the tank.
Check actual power to the GP's and the resistance of each plug.
Fred.
Fred Moir.
Lynn MA.
Diesel preferred.
________________________________
From: Mercedes <mercedes-boun...@okiebenz.com> on behalf of Larry
Turner via Mercedes <mercedes@okiebenz.com>
Sent: 25 December 2016 19:46
To: mercedes@okiebenz.com
Cc: Larry Turner
Subject: [MBZ] HELP!! My '91 300D is Not Starting
Tried to do some last minute shopping Thursday and she wouldn't fire up
without some very extended cranking.
It's very rare for it to take more than a few revolutions of the
engine. So I replaced all of the Glow Plugs just in case, but it didn't
help.
I don't think it is the Glow Plug Relay because it usually tries to
start after cranking for 10-15 seconds, but this time I am getting
nothing! It's not trying to start at all. Saturday before I changed
the GPs, I got it to start by cranking it. It started firing on 2 then
three and finally it was on 4 and 5 I think.
BTW, I did a Oil Analysis on it last year and all the numbers came out
exactly where they should be. Very low metal contamination, no water
content and almost no fuel content. Also, the fuel mileage has stayed
stable at 30 mpg +/- 2 mpg.
I will test the Relay tomorrow just in case. *Any ideas?*
Thanks,
LarryT
'91 300D 2.5 Turbo
280,000 miles
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