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Discussion Starter · #1 ·
I have 10,000 miles on a PZEV ZX5 with problems that I don't quite understand.

Issues:
1. I like the power at 4500rpm and above but the transition from weak econo-box below 4500 to the wanna-be monster above 4500 is horrible. It's like fuel completely stops going to the engine for a half a second and then the thing leaps forward like hell. Makes judginf what the car is going to due a little difficult. Is there a way to smoth it out? Are they all like this? Is there a way to keep it in the "wanna-be monster mode"?

2. From the first day I had the vehicle, it bucks and stutters at a cruising RPM. Goes like this: If I am accelerating or decelerating it's smooth. If I am just cruising at a maintained speed these subtle bucks and flutters start happening. I took it to the Ford dealer (long story there) and they came up with nothing. They replaced the ECU to make me feel better and it made the problem just a little worse. Has anyone else experienced this? It makes me hate an otherwise great car.

If anyone else had the issue and got it fixed, please let me know what you did and how you talked the dealer into realizing your car actually had a problem. Thanks!
 

· Mr Know-It-All
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Mine usually stays above 4500RPM so I can't say I've experienced your problems.


I don't notice any huge jump in that range either, and I've driven cars like the Integra Type-R, Celica GT-S and Honda S2000 where you do feel a noticable change at certain point in the rev-range. You might have them take a closer look at your intake manifold as there are flaps inside that open and close at certain RPMs. I don't believe they are mechanical, I think they work off of vaccuum pressure. Someone can correct me if I'm wrong. You might also have them check your MAF sensor and throttle body as other sources of the problem you are experiencing.

As far as cruising, there are times when I've popped the cruise control on and it seems to glide along with no problems. I'm pretty sensitive to what my car is doing, so if there was anything to gripe about with my car, I'm sure I would have noticed.

>8^)
ER
 

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auto or manual, cruise control or no, stumbling happens at any rpm or only in a specific range?
 

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Where do you live, higher elevation? I dont know how it works or if it even matters, but I live in Spring Valley Lake in the High desert and elevation is around 3,000 feet. And for some reason my cars doesnt run good on 87, I only put 91 in it, Do you always go to the same gas station, do you buy Arco or worse, just a thought maybe that could be your problem if its not mechanical or electrical.
 

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Discussion Starter · #5 ·
Happens at all elevations and with different gas types from different stations (Shell or Texaco). I was in California when I bought it and only ran 91 octane, now I live in Texas and put 93 in it. No change from that.

It's a manual. No cruise comtrol. It doesn't really have a specific RPM range. Just that you have to be cruising down the road, maintianing speed, no acel or decel. I happens anywhere between 2000 and 4500 rpm. Happens at a steady 35 mph going to the store or at 70mph going down the freeway, just as long as your speed and RPM's are stable with No acel or decel.
 

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Discussion Starter · #6 ·
The jump between "low power" under 4500 and "high power" above 4500 is so severe sometimes that if I am doing it in 2nd gear the tires will loose a little traction. It really dies down for a fraction of a second and then REALLY surges. The Ford dealer said this was normal for a PZEV.

Is this not what all you other PZEV drivers are experiencing? That would sure be some useful info the next time I hit the dealer up.
 

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Happens at all elevations and with different gas types from different stations (Shell or Texaco). I was in California when I bought it and only ran 91 octane, now I live in Texas and put 93 in it. No change from that.

It's a manual. No cruise comtrol. It doesn't really have a specific RPM range. Just that you have to be cruising down the road, maintianing speed, no acel or decel. I happens anywhere between 2000 and 4500 rpm. Happens at a steady 35 mph going to the store or at 70mph going down the freeway, just as long as your speed and RPM's are stable with No acel or decel.
I doubt its the prob, but your car is made to be run on 87 octane, maybe that has a small part in the stuttering?

I also do not experience the "surge" after 4500 RPM. Verra strange man. Try to hook up with a fellow PZEV in Texas, post in the Texas forums, and see if theres a PZEV dude in your area that will letcha test drive his or vice versa to test if yours is diff.
 

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93 is harder to ignite than 87, so the car *might* not actually be combusting the fuel well enough.

try a few tanks of 87 and see if the prob disappears, since you're stock, there's literally nothign but disadvantages to higher octane.
 

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Don't our cars have a dual runner intake manifold (or whatever) like the SVT? So, at low rpm it is pulling air through a long runner, and at hi rpm threw a short runner.

Could that be the cause of his problems?
 

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93 is harder to ignite than 87, so the car *might* not actually be combusting the fuel well enough.

try a few tanks of 87 and see if the prob disappears, since you're stock, there's literally nothign but disadvantages to higher octane.
Where do u get your info man, it's made to run at 87, but higher octane will better performance even if u don't feel it. I visited Texas for Xmas and enjoyed the smoother running engine using 93, instead of Cali 91.

The problem could be one of your cats, some guys have been having their cats replaced from being clogged. Maybe that will help.
 

· Inheritly Sinister
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Don't our cars have a dual runner intake manifold (or whatever) like the SVT? So, at low rpm it is pulling air through a long runner, and at hi rpm threw a short runner.

Could that be the cause of his problems?
Not runners, but we have tumble flaps that operate around 4000-4500.
 

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Well, could those tumble flaps cause somthing like this? That is right around the range that they would operate.


Higher octane=wasted money


I ran 91 in mine for the first month or so, and noticed no differance when I went to 87.
 

· Inheritly Sinister
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93 is harder to ignite than 87, so the car *might* not actually be combusting the fuel well enough.

try a few tanks of 87 and see if the prob disappears, since you're stock, there's literally nothign but disadvantages to higher octane.
Where do u get your info man, it's made to run at 87, but higher octane will better performance even if u don't feel it. I visited Texas for Xmas and enjoyed the smoother running engine using 93, instead of Cali 91.

The problem could be one of your cats, some guys have been having their cats replaced from being clogged. Maybe that will help.
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
http://www.techweasel.com/articles/octane.htm
http://greennature.com/article347.html
http://www.carjunky.com/news/newtext/40.shtml

Higher octane does not mean better performance. Period.
 

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93 is harder to ignite than 87, so the car *might* not actually be combusting the fuel well enough.

try a few tanks of 87 and see if the prob disappears, since you're stock, there's literally nothign but disadvantages to higher octane.
Where do u get your info man, it's made to run at 87, but higher octane will better performance even if u don't feel it. I visited Texas for Xmas and enjoyed the smoother running engine using 93, instead of Cali 91.

The problem could be one of your cats, some guys have been having their cats replaced from being clogged. Maybe that will help.
Misinformation much?


Definitely check out some of those sites that Egz posted.
 

· Mr Know-It-All
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Where do u get your info man, it's made to run at 87, but higher octane will better performance even if u don't feel it. I visited Texas for Xmas and enjoyed the smoother running engine using 93, instead of Cali 91.

The problem could be one of your cats, some guys have been having their cats replaced from being clogged. Maybe that will help.
Just to add to what the others have posted, if your ECU is not designed to take advantage of higher octane fuels, or isn't does not require them, then there is no benefit to using them and you may find it is actually a detriment to the combustion process. The myth that higher octane fuels are better for all cars is simply not accurate.

>8^)
ER
 

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Discussion Starter · #17 ·
I have to admit, I am a victim of the "Octane Myth." Thanks for the links to the articles. The cool part is the car is low on gas and I need to go fill up after work. Thanks for the info, I'll let everyone know how it goes.
 

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I've had a couple cars with ford dual stage intakes and I don't remember any problems while at steady speed.

you'd get a stumble while accelerating if the changeover didn't take place at the right RPM, but if you're at a steady speed, it shouldn't be having any issues.
 

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Mine used to stutter going around 40 mphs in about 2000 rpms but now with the intake and exhaust from focus sport its gone completely the car runs beautiful better gas mileage too alot better
 

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I just helped my friend buy a 99 toyota solara. I was flipping thru the owners manual and it said that the car was made to run on 87 octane, but for best performance use 91 or higher octane. Me and Toyota must be stupid. Oh and racers as well who use 110 octane.
 
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