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Long Vacuum Question.....HELP!

1240 Views 8 Replies 5 Participants Last post by  Pimp_scort_89_GT
Hi all!
I´ve been troubleshooting a hesitation problem for quite some time now and I´m stumped. It´s a 92 GT...135k on it; I´ve had it since new. I must say first off that I have a bad lifter or 2, that are noisy on startup in the no2 cylinder.
Compression is 150/150/125/150.

My problem is that my mileage is really going down in the last 6 months. I´m down to about 24mpg; and the "kick" that used to happen at 3k rpm no longer does. On the freeway, going up a hill (lots of ´em here in Seattle) I can now start to feel stuttering. but it´s consistent and rhythmic hesitation, about every 1.5 to 2 seconds the car hesitates for a moment; as if someone is pressing the A/C button every 2 seconds. NOTE: mileage and running was fine for a year after I found the low compression; so I don´t think it´s related to that. Burning a valve also wouldn´t be so sudden (IMHO).
First thing I did was disconnect A/C and PS speed sensor. Still did it.
Next thing I did was run vacuum test to find out if my valve WAS a problem. Vacuum is rock steady at idle (surprised me considering my stuck valve), and under WOT as it should be.
However under equilibrium (say hold rmp at 3k), the vacuum needle swings WILD between both stops.
Thought maybe the Cannister Purge solenoid was bad.
Ran as many of the pinpoint tests (from the shop EVTM and Emissions books) I could do without a vacuum pump and did not find any problems. All the vacuum hoses are fine, and it has a brand new fuel pump/cap/rotor/plugs/wires etc. Also brand new PCV. Rubber intake tube to TB is 2 years old (yeah, cracked like an sob after years)
Still does it.
Has anyone else seen this vacuum guage behavior? Any ideas on what to check next? I can´t imagine this is normal; I´ve never seen this type of vacuum reading EVER!
Anything; any digs in the dark would be appreciated.
I have 2 spare complete engines (for future turbo plans) so maybe I´ll start swapping parts to see what happens; maybe even replace the bad lifter just to see since it´s not too hard to get a cam out. Otherwise I´m just going to deal with the crappy performance until I can get the dough to do up a turbo and drop it in.

1988 Thunderbird Turbo Coupe
1992 EGT
1971 Mustang BOSS

[ This message was edited by: Boosted on 12-01-2003 05:03 ]
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Think I may have your answer. I remember reading about this in one of my school books, so I took it off of the shelf to see what I could find. This is what I came up with:

Reading at idle is relatively steady, but the needle oscilation becomes more pronounced as RPM is increased. Possable problem : Weak valve springs.
While we are on compression numbers, I just have to post my findings for the 1.9 I had in the Scort after the timing belt broke. If I remember corectly it was something like 150/110/35/90. Amazingly the engine still started up after I replaced the timingbelt. I tried driving it down the street and I was getting passed by turtles so I turned around and paked it infront of the engine hoist.
Could be a valve floating, or bouncing off of it´s seat due to the weak springs causing a loss in power that could be making the engine bog.
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