Hesitation at middle RPM under moderate load
in [Toyota]
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From: Hachiroku ハチロク on 22 Jul 2010 20:14 The car in this case is a 1989 Mazda 626. It was running great until the day before yesterday, and turned 190,000 miles last week. AT highway speeds it hesitates only a little bit, unless you start going up a hill, then it starts sputtering. Normal around town driving, not so much, unless you're going up a hill in third gear. Usually occurs around 3,000 to 3,500 RPM. Once you get about 3,500 it smooths out unless going up a hill. I went for the "easy fix" first and replaced the fuel filter. WHen I got the 'old one' out (it's only 32,000 miles old...) the fuel that was in it ran right out and was mostly clear, with a reddish tint as it ran down. Not muddy like the last time this happened to me. At 152,000 I replaced the plugs, wires and all filters. About a year ago I added a cap and rotor from a dealer's "New old stock". Some guesses: pressure regulator. I hope not. AutoZone price $123. Wires. I used genuine Autozone "DuraCrap" wires, so this was the second thing that popped into my head. Fuel filler cap? Recently I noticed it spins on easier than it used to. Fuel...the last two fillups were at the same Gulf station, and at 93 Octane, since it's only 4 cents more than mid grade. I threw in a bottle of Techron in case it's a sticky injector ($162 at AutoZone...) I'll have to check Mazda's prices...on some parts they're less expensive than AZ. I'm betting on plug wires crapping out...
From: nm5k on 22 Jul 2010 21:52 On Jul 22, 7:14 pm, Hachiroku $B%O%A%m%/(B <Tru...(a)e86.GTS> wrote: > The car in this case is a 1989 Mazda 626. It was running great until the > day before yesterday, and turned 190,000 miles last week. > > AT highway speeds it hesitates only a little bit, unless you start going > up a hill, then it starts sputtering. Normal around town driving, not so > much, unless you're going up a hill in third gear. > > Usually occurs around 3,000 to 3,500 RPM. Once you get about 3,500 it > smooths out unless going up a hill. What you describe is what happens when the intake valves get carboned up. The Techron was a good idea. It will clear that stuff up, but it takes a while. Course, it could be running lean due to other problems, but keep the possible carbon in mind. It's pretty common. What happens is the carbon snow cones behind the intake valves, and when under a heavy load, or when hot, the carbon will expand and keep the valves from fully closing. So you start losing compression. Remove the heavy load, and it starts running right again. The carbon also soaks fuel and can cause lean running. The only real way to tell if it's a fuel pressure problem is to actually hook a fuel pressure gauge to the engine. A car with a super carbonized engine will quit running once it gets hot enough. We had a Camry that had that problem. The dealer had it for two weeks and never could find the problem. They blamed it on the wiring harness, and charged us a load of money for not fixing the car. I ended up finding the problem myself, which was severe carbon. Anyway, like I say, it may be something altogether different. But keep the carbon in mind, cuz I've noticed most mechanics won't think of it. The Camry was in three different shops, the third being the dealer for two weeks. None of them could figure out the problem. It took me a bit of pondering before I found it. The first thing I did when I drug it back from the dealer was to check the wiring harness, which the dealer claimed was uncheckable. :( It took me about an hour to check every single wire in the harness. So much for uncheckable.. Never tell an extra class ham a wire is uncheckable..They will never believe it. I know I didn't. :/ I had to build a pressure gauge, and after checking the whole car out, could find no obvious problems. But it still wouldn't stay running once it warmed up. But I finally found the problem after noting the loss of compression when it did it. The starter would spin faster than usual, and often erratic due to the loss of compression in some cyl's, but not all. I ran a long hose for the fuel pressure gauge and was watching it as I drove. It was fine and never dropped from normal. If it's carbon, it will keep getting worse until the point on steep grades it will totally quit running after a while. Super bad, and it will quit running when it's hot, no matter what load you are putting on it. Keep running the Techron for a while. Two bottles worth will knock it out enough to tell if it's carbon or not. Maybe even one bottle if it's not too bad. Then again, I guess it could be an ignition problem.. :/ It's all a guessing game when you are on the interweb and can't see the malfunctioning machine.
From: JoeSpareBedroom on 22 Jul 2010 22:08 "Hachiroku ????" <Trueno(a)e86.GTS> wrote in message news:4c48df07$0$74748$afc38c87(a)read01.usenet4all.se... > The car in this case is a 1989 Mazda 626. It was running great until the > day before yesterday, and turned 190,000 miles last week. > > AT highway speeds it hesitates only a little bit, unless you start going > up a hill, then it starts sputtering. Normal around town driving, not so > much, unless you're going up a hill in third gear. It means something's not right.
From: Tegger on 22 Jul 2010 22:22 =?iso-2022-jp?q?Hachiroku_=1B$B%O%A%m%=2F=1B=28B?= <Trueno(a)e86.GTS> wrote in news:4c48df07$0$74748$afc38c87(a)read01.usenet4all.se: > The car in this case is a 1989 Mazda 626. It was running great until > the day before yesterday, and turned 190,000 miles last week. > > AT highway speeds it hesitates only a little bit, unless you start > going up a hill, then it starts sputtering. Normal around town > driving, not so much, unless you're going up a hill in third gear. > > Usually occurs around 3,000 to 3,500 RPM. Once you get about 3,500 it > smooths out unless going up a hill. Got EGR? Checked that"? -- Tegger
From: Hachiroku ハチロク on 22 Jul 2010 23:13
On Thu, 22 Jul 2010 22:08:48 -0400, JoeSpareBedroom wrote: > "Hachiroku ????" <Trueno(a)e86.GTS> wrote in message > news:4c48df07$0$74748$afc38c87(a)read01.usenet4all.se... >> The car in this case is a 1989 Mazda 626. It was running great until the >> day before yesterday, and turned 190,000 miles last week. >> >> AT highway speeds it hesitates only a little bit, unless you start going >> up a hill, then it starts sputtering. Normal around town driving, not so >> much, unless you're going up a hill in third gear. > > > It means something's not right. Gee! Uh, thanks, Joe! |