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hesitation below 2500 rpm -maf?
Posted 20 October 2003 - 08:49 PM
Posted 20 October 2003 - 09:46 PM
Posted 20 October 2003 - 11:10 PM
And... yes. My XT does the same freeking thing!! Now that is a bit different, since my XT has a disty. The XT will ping on 89 octane, and only wants 91 octane. The disty is as far retarded as possible, leading me to believe it's a tooth off on the cam. That will be attended too as soon as my friend will lend me his timing light:-\
Posted 21 October 2003 - 07:45 AM
My knock sensor died some months ago so that was replaced. I replaced spark plugs, air/fuel filters and 02 sensor but nothing helped. When i disconnected the battery a few months ago and cleared the ECU, i think that was went away for almost a week but then the hesitation and rough shift from 1st to 2nd came back too.
Oh well, will have to live with it.
How does one use a timing light? do i have to have the timing cover off to get the reading?
Posted 21 October 2003 - 08:09 AM
Posted 21 October 2003 - 12:05 PM
These engines are known for running rich and building up carbon. I recall Emily of CCR Inc posting one time that when they tear down one of these engines, you'd think you were dealing with a carburated engine from the '70's.
What I experienced was hesitation while taking off from a stop, or during very very slow motion (eg, parking lot). Idle was fine, but it would bog between 600 and 1000 rpm. As it got worse, it crept up into higher revs. If I was loafing thru town with the engine turning over at about 1400 or 1500 rpm, I could feel little jerks, almost like a misfire. Easing into my garage to park (tight space) became quite the challenge with the ragged throttle response. However, if you put your foot into it a bit, it would be fine. Trying to "feather" the throttle was where it really showed itself.
My dealer did the MotorVac procedure on my car. This runs cleaner thru the fuel rail and injectors for several minutes, then the cleaner is run thru the engine. (As I understand it.) I don't know if the fuel rail / injector portion matters or not to be honest. Anyway, the problem disappeared. I was around 100k miles when this first happened. The diagnosis of carbon left me a little speechless. These cars have ECU's, MAF, fuel maps, etc., and I do 90% highway driving. Whodathunkit.
Over time, I would sense it coming back. A bottle of cleaner or a tank of premium would usually fix it up. Until recently, around 200k miles now. I've been trying to avoid doing another MotorVac (for various reasons).
I changed out the O2 sensor. That helped considerably. Although no CEL, it was probably going and causing the mixture to be even more rich. My gas milage had slipped a little (maybe 5%), and that has improved again with the new O2 sensor.
I've been meaning to try the "water" treatment to "steam clean" the engine. I just haven't gotten to it. (There was a post recently about this.) For right now, I'm living with it. I have to wonder if the MAF might be going. I know it can cause issues like this. Personally, I think it is still residual carbon.
Of course, there can be many other reasons as discussed in the prior posts. But if you've ruled them out, then it might very well be carbon build up.
For what it's worth...
Posted 21 October 2003 - 12:46 PM
Engine stopped missing intermitently at idle last year when I put a bottle of the strong kind (good for 5,000 kilometers they say) of fuel system cleaner through the system (gas tank variety)
I'm preparing to do the same shortly but also bought a complete system (80$ Can) that I will administer next spring: box comes with throttle cleaner, gas tank injector cleaners, oil anti acid (?) and a bottle of metered cleaner you connect to the intake manifold thru the PCV.
I'll report on the result then.
I suspected the engine was running rich and that carbon was building up (most of the time the exhaust pipe is black with at least a thin layer of soot).
But the only symptom I've had is an intermittent miss (one in a while) at idle (that dissapears when i do the treatment). Never an hesitation accelerating or cruising.
Posted 21 October 2003 - 06:07 PM
Instead of using water in the vacuum of the throttle body, I've let the engine suck up a can of Seaform Motor TuneUp - good results.
96 OB w/125K
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