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monty101
User
Aug 10, 2014, 5:00 PM
Post #1 of 14
(1990 views)
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1997 chevrolet, blazer 4.3 ltr 100000 miles
My 1997 4.3 blazer leakdown test shows in 30 minutes after
I shut it down the pressure will drop from 60 to 25 lbs. It holds the
60 lbs for 15-20 minutes but then instantly the guage shows it drops
to 40. It will graduately drop down to about 25 over the next 15
minutes. DoI have a problem.
I am trying to determine if the leakdown
I am experiencing is the reason that sometimes the motor
has to crank a lot longer to start the motor. If I do have a
leakdown problem how do I determine whether the leak
is from the 12 month old acdelco fuel pump check valve or
the 12 month old delphi spider I installed last year.
I am running a can of seafoam through it right now. I am hoping
the seafoam with fix any problem I may be having with the fuel pump
check valve.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 10, 2014, 5:33 PM
Post #2 of 14
(1978 views)
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I don't think that amount of leakdown is serious enough to cause the long crank but you can put a fuel pressure gauge on it before starting it to see how fast it builds up.
Another possible cause is a bad fuel pump relay. The oil pressure sender supplies a redundant power supply to the fuel pump after it builds oil pressure. Watch the gauge and see if the pump primes by merely turning the key on.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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monty101
User
Aug 10, 2014, 6:14 PM
Post #3 of 14
(1971 views)
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Do you know why the pressure stays the same at 60 for 15-17 minutes and
then suddenly drops to 40. Is it supposed to do that?
I thought my fuel pressure guage was broke but it has done that 3 times so I guess the guage
is right.
I don't understand why the leakdown of pressure can make it crank
and crank and sometimes never start. Is it because the line fills up with
air and there is a air bubble in the line that the gas has to push out the
injectors before the gas from the pump gets to the motor. Does the fuel
pressure guage reflect the pressure on the air forcing out as fuel pressure
too even though its air pressure.
It usually will start after the 3rd try but yesterday it took about a half hour to
get it to start up. I must have tried 10-15 times. It had only been setting there over nite.
If it does not crank would it help if I pressed on the scrader valve and let the air out??
Kinda worried that until I figure out what is wrong I may get stranded somewhere.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 10, 2014, 6:17 PM
Post #4 of 14
(1970 views)
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I already told you, the leakdown is not your problem.
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monty101
User
Aug 11, 2014, 6:21 AM
Post #5 of 14
(1957 views)
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The guage showed no pressure. I turned on the key and it jumped to 58 lbs and started right
up. I turned off the engine and the guage dropped to 55 and held. I turned on the key and it
did not jump to 58 again, it dropped to 52 and held and then started. Its always jumped to 58 or
60 when I turned on the key in the past. So, I turned off the key and it stayed at 52. I switched
it off and switched it on and it stayed at 52. Did it again and it stayed. I then did it again and it
jumped to 60 turned off the switch and it held. Maybe my problem is intermittent
and sometimes it just goes to 49. If that happened then it would never start.
I don't know if a relay is the problem but I can get a new one for 16 bucks. I think I will get one.
Maybe that's why it appears the pump did not turn on when it dropped to 52 when I turned on the key.
It stayed at 52 when I turned it off and turned it back on. Like I said if that had been 49 it would
not have started. Something's not right unless it had a air bubble in the line and I guess that
might cause the same problem but I really don't know.
I had pcmforless tune up the pcm to get better gas mileage I will call them. I know he changed
the timing because it turns over a lot faster now but it does get better gas mileage.
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kev2
Veteran
Aug 11, 2014, 7:30 AM
Post #6 of 14
(1947 views)
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does NOT sound like leakdown is your problem.
Scan for codes ESP if the CEL is OFF...
Tell us how the timing was changed? That is important to know.
BASICS -
plugs - what kind and what is appearance?
engine is STOCK?
Have you looked at ECT?
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 11, 2014, 7:50 AM
Post #7 of 14
(1944 views)
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Yes, I would change the relay. Also inspect the contacts in the socket for any burnt ones.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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monty101
User
Aug 11, 2014, 7:51 AM
Post #8 of 14
(1943 views)
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put in a new relay....Still it appears sometimes when you turn the switch on the
guage does not move when it is down to the low 50 range. Then sometimes the
guage will jump up to 60 lbs. I think it means that the pump is not coming one when
you turn the switch on and its at 52 and the guage needle does not jump.....If so
and the relay is new then I'm guessing its the starter relay switch in the
steering column or there's an air bubble in the line.....Not sure what to do. I will call
PCMFORLess next
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 11, 2014, 7:55 AM
Post #9 of 14
(1941 views)
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You still have a fuel pump priming problem. Check the relay socket and fuse sockets as I suggested.
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monty101
User
Aug 11, 2014, 8:36 AM
Post #10 of 14
(1937 views)
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I checked they aren't burned.
I did call PCMforLess and he said the motor turns over faster because he adjusted the
timing but what he did would not cause any problems that would result in the motor
not starting. He also told me the PCM is not responsible for the sudden drop in pressure
from 60 to 40 lbs after 15 minutes.
Only thing left is the starter switch in the steering column.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 11, 2014, 9:26 AM
Post #11 of 14
(1935 views)
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WHAT?
Go find yourself a different mechanic. I don't know who this guy is trying to snow but that ignition timing is not adjustable by any means on that engine.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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monty101
User
Aug 11, 2014, 9:56 AM
Post #12 of 14
(1933 views)
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Yeah.....when I first started testing the pressure it only held for about 5 seconds. Then I drained all
the gas and put in a can of sea foam thinking maybe the check valve had some varnish on it causing the
leak down. Put in 5 gallons of gas and let it run for a hour. Then it held for 15 minutes and started this
20 lbs drop routine after it had set for 16 minutes.
I put the new relay in like you suggested and you can hear it clicking so I know its working.
Now its held fuel pressure at 58 pounds for an hour......It may be fixed. I will like you advised keep
the guage on it sticking up through the hood and monitor it for a while.
Its always possible the guage may have been acting up causing the weird drop after 15 minutes. Maybe
the sea foam is cleaning up the guage internally and it has started working right......
Oh I know you can't adjust the timing with a timing light and he would not tell me much. He was referring to
the computer. He reprogrammed it and he probably just told me he had advanced or retarded it. He would
not get real specific "protecting his turf" and just told me he advances or retards the motor which makes it
start easier. It does get a heck of a lot better gas mileage now....It gets around 20mpg when I have
checked it after driving it both in town and on the highway. Around town it gets about 2 mpg better
which adds up with gas getting so expensive. I him do other stuff to the computer besides the tune
up too. I want to get it out on the highway and see exactly how good it will be. It was getting 21 miles
per gallon. I would not be surprised to find out it gets 25 on the highway now....
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 11, 2014, 10:10 AM
Post #13 of 14
(1931 views)
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He cannot change the base timing no matter what he does. That is determined by the Crank Sensor. He may be aable to mess with the advance curves but that has nothing to do with starting.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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monty101
User
Aug 11, 2014, 10:16 AM
Post #14 of 14
(1929 views)
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Yeah like I said he knew I didn't know enough to question what he was
telling me so he decided to snow me and say something that that was not
even possible and therefore would not make it possible for me to do the
work myself. Like I said he was protecting his turf. Secret stuff he did
but it worked because its getting a lot better gas mileage. ... Thanks for helping me.
(This post was edited by monty101 on Aug 11, 2014, 10:29 AM)
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