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Mikeymik
Novice
Sep 25, 2012, 3:30 PM
Post #1 of 10
(2940 views)
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Rough idle & stalls
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VEHICLE:
Owned since new: 92 Chevy P/U C1500 - 4.3 z motor - TBI fuel injection - 2wd - manual trans - 325,000 miles
Old & Ugly but normally runs great and very reliable; had recent tune up of plugs, wires, cap, rotor, pcv, air filter
SYMPTOMS:
Became harder to start 3-4 times, then very rough idle & stalls, had to pump pedal vigorously to keep from stalling, won’t accelerate in neutral and wants to stall when pedal depressed. No check engine light at all.
WORK DONE:
My mechanic of 10 years said fuel pump was bad. He cut the rusted sending unit from the rusted fuel lines, said it was not worth fixing, and told me to tow it away with the fuel tank in the bed.
Replaced the fuel pump, sending unit, and fuel lines myself in my driveway.
Had same starting conditions as above. I used Chilton manual and multimeter to test TPS w/ key on (had 5 v on feed wire, low 0.45 v on signal wire at idle should be 0.5 – 1.2 v, signal wire went smoothly from 0.4 - 4.5 v and back down with key on); IAC valve had normal Ohmic readings; MAP sensor had normal 5.0 v on feed wire, totally abnormal voltage readings of 4.6 with key on and while running had 4.6 - 4.9v from idle through high acceleration (with hose disconnected). MAP hose is intact and has good suction.
When I disconnected MAP sensor from hose and electrical connector it started right up w/ check engine light on, accelerated powerfully in neutral, idles normally for a minute or so but will stall without a quick pedal pump, then back to normal for a minute or so . . . .
Replaced TPS and MAP sensors.
RESULT:
Still have same problems I started with, no check engine light. This time a small flame shot up from the TBI. Please help.
(This post was edited by Mikeymik on Sep 25, 2012, 3:49 PM)
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nickwarner
Veteran
/ Moderator
Sep 25, 2012, 6:05 PM
Post #2 of 10
(2870 views)
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Re: Rough idle & stalls
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What is the fuel pressure at now?
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Mikeymik
Novice
Sep 27, 2012, 12:24 PM
Post #3 of 10
(2823 views)
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Re: Rough idle & stalls
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I believe the specs call for 9-13 PSI. I hooked up a new Actron fuel pressure tester (0-100 psi dial) in line behind the fuel filter. Zero pressure indicated with key on. Checked fittings and they seemed tight. Again no reading with key on. With the MAP sensor hose disconnected, it started right up and idled well for a minute then quit. Still no pressure readings at any time.
The pump, sending unit and rear lines are all brand new. I am fairly well certain I tightened all hose clamps and seated the O ring on top of the tank properly before raising it into position. I don't see obvious any fuel leaks. I even disconnected the return line to insure the lines weren't crossed and it still started and ran well for a minute, several times. The fuel cap is an old locking piece of junk that should be replaced but I'm not sure that would cause this.
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 27, 2012, 12:33 PM
Post #4 of 10
(2817 views)
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Re: Rough idle & stalls
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You'd better find out if that fuel pressure gauge is working or not.
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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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Mikeymik
Novice
Oct 1, 2012, 8:45 AM
Post #5 of 10
(2757 views)
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Re: Rough idle & stalls
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New fuel pressure guage barely flickers with key on, engine starts right up and idles well for a minute with 6 psi, no change at stall, pressure drops to 0 psi over 30-45 seconds after stalling.
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Hammer Time
Ultimate Carjunky
/ Moderator
Oct 1, 2012, 8:47 AM
Post #6 of 10
(2754 views)
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Re: Rough idle & stalls
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I find it hard to believe that engine will even run on 6PSI. Find out where you're losing that pressure.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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Mikeymik
Novice
Oct 1, 2012, 8:57 AM
Post #7 of 10
(2749 views)
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Re: Rough idle & stalls
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What would you suggest?
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Hammer Time
Ultimate Carjunky
/ Moderator
Oct 1, 2012, 10:11 AM
Post #8 of 10
(2737 views)
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Re: Rough idle & stalls
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Do some troubleshooting and find out where the pressure is going. You can pinch off the return to find out if the pressure spikes and whether the regulator leaks down.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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Mikeymik
Novice
Oct 22, 2012, 9:12 AM
Post #9 of 10
(2622 views)
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Re: Rough idle & stalls
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I pinched off the fuel line between the pressure guage and the fuel injectors, no change - still had 6 psi pressure reading. Let the truck sit for 2 weeks and then it cranked but wouldn't start at all. Pinched it off again at same place with 0 pressure this time. Switched out the new fuel pump for a another new fuel pump - and now we're back on the road heading toward 400 k miles.
Thanks for your help, please close out the thread.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Oct 22, 2012, 9:17 AM
Post #10 of 10
(2620 views)
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Re: Rough idle & stalls
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Locked at your request.........
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