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Discussion Starter · #1 ·
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.
Thanks!
Matt

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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Mine does the exact same thing but it used to be just temporarily but know it stutters through every gear until I get up to like 4k. I replaced the intake tube the vaccuum hose and plugs, the only thing else I need to do is replace the fuel injectors cause evryone says that it´s them but I don´t know what to do, i´ve had shops tell me it is an airflow problem and other shops tell me it is a fuel injector problem. I´m stumped.
 

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Discussion Starter · #3 ·
Wow, nice to know I´m not the only one.
I´ve been told the same things as you. Engine shakes like timing is out until about 4k, right? Idle´s with a bit of a bump, and sometimes almost "lopes"? A bunch of flat spots until 4k?

I´m going to run some more pinpoint tests and swap distributor.
Kind of leaning to dirty pot on the VAF; or maybe bad FPR.
If I find something I´ll let you know. Unless someone else has fixed a problem like this??
 

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You know being boosted I have noticed vac/boost is really touchy. Never consistant...and kinda scary. My last compression test last month showed 150 - 160 - 150 - 150. The only thing I can think of is the VICs system. It´s vac activated and will open up the second set of runners at what´s supposed to be 5k revs. The vac storage canaster could be leaking (well I mean the check valve that holds the vac in there?)

I hate to admit it but the Mazda BPD8 is a VERY technically engineered motor. I would even say it has tighter engineering then any honda motor. Very hard to figure out too. I wish it was easier to be honest.
 

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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.
 

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I think you guys have may both have a valve sealing problem. by comparison you compressio numbers are a little lower than what I had come up with from my 1.8 I had between 180 and 185 on all four holes. run a leakdown test and see what you get.
 

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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.
 

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Discussion Starter · #8 ·
Hhhmm. Sounds like valves.
Compression is a bit low...I did beat this car for 10 years.
Thanks for the info. The one thing that gets me is the power oscillation.
Today in neutral with my foot steady at 3,000 rpm, there was still a load apparent every second or so. Like the A/C cycling; but if I push the button, I can tell it comes on at that point.
But valves.....yeah.
 
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