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emokid711
New User
Dec 21, 2007, 8:37 PM
Post #1 of 7
(3706 views)
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i have a 97 gmc yukon with the 350ci vortec in it .... i drove it home today for lunch and it ran ok . upon trying to leave it wont start .... it cranks and backfires but nothing else .... i checked and i have spark and fuel ... not sure on the fuel pressure but i know the fuel is there .... any ideas???
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Guest
Anonymous Poster
Dec 21, 2007, 8:56 PM
Post #2 of 7
(3702 views)
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perhaps the timing jumped
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 22, 2007, 4:00 AM
Post #3 of 7
(3697 views)
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Crank sensor highly likely. Might behave like an old type cracked/wet distributor cap if so,
T
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emokid711
New User
Dec 24, 2007, 2:21 PM
Post #5 of 7
(3678 views)
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any ideas ? i found a bad distributor cap . .... but still wont start ..... fuel pressure is good
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DanD
Veteran
/ Moderator
Dec 25, 2007, 5:44 AM
Post #6 of 7
(3674 views)
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There were two different injection system that were used that year on the 5.7 (350) engines.
If yours has the CSI (central sequential injection) the fuel pressure specification is 60-66 psi.
If your pump is only producing, lets say 59 psi; there’s a good chance it won’t start, that’s how fussy the CSI systems are for the proper pressure.
I’m not saying this is your vehicle’s problem or this is what you’ve done to check fuel pressure, but sticking something in the test’s port’s valve (like what a lot of people do); watching fuel spray all over the engine is not a viable test.
You need to have an accurate pressure gauge attached; pressure tested while cranking with a fully charged battery.
I’ve seen weak pumps run one of these systems all day long, if you get engine to start. That’s because while the engine is running battery/system voltage is being kept up full by the charging system; spinning the pump just that little bit faster; shut the engine off and it may not restart.
I’ve had a number of customers come in saying that they’re having problems starting their van or truck? They say it’ll crank ok but they have to use booster cables to jump start the thing. It’s hard too get them to believe that the problem is their fuel pump; for the same reason that I explained above.
Now if this truck has SFI (sequential multiport fuel injection) they are not as bad for having full fuel pressure available for starting. Low fuel pressure on these systems will usually give you driveability issues, like lack of power.
SFI systems use individual electro magnetic injectors for each cylinder; regardless of fuel pressure the injector is going to open. CSI uses one “central” metering valve that controls the length of injection and a number (six or eight cylinders) of poppet injector nozzles that uses fuel pressure to open, somewhat like a diesels injection system.
fuel pressure is good What is your vehicle's actual fuel pressure?
Oh yea
 MERRY CHRISTMAS
Dan.
Canadian "EH"
(This post was edited by DanD on Dec 25, 2007, 5:58 AM)
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emokid711
New User
Dec 25, 2007, 11:26 AM
Post #7 of 7
(3666 views)
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i will get a gauge when i return to work on wensday and check the pressure . ... i know that its an sfi system
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