Lousy Acceleration/Timing Woes - NoPistons -Mazda Rx7 & Rx8 Rotary Forum

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Lousy Acceleration/Timing Woes

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Old 11-06-2005, 10:51 PM
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Hi everyone, new user here with an '87 Sport.

I've been reading through the faq's for a while now and playing with my car and unfortunately my first post has to be about troubles with the car -I'm having some power issues.

I bought the car with a rebuilt and mildly ported engine, and for being brand new

and ported, the car was an absolute turd under acceleration under all RPMs.

The problem is it accelerates literally like a 1980's toyota camry, 0-60 upwards of 10 seconds for sure.

It feels like the car 'wants' to accelerate, but it's being held back by an anchor.



Things I've checked :

Plugs and wires cleaned/replaced

Oil and coolant are all new and topped off

Mileage is normal for an rx7

Air filter is clean

Exhaust is a custom header to small cat to single muffler with 2 1/2" the whole way

TPS is to spec

Idle is about 900 and steady

6ports are working (verified by grease chunks, then by wiring open)

TIMING



Now the timing is interesting - following procedures from the handbook, I can manage to line up the first yellow mark with the timing pin. When I switch to the trailing wire, the yellow mark is still lined up with the timing pin i.e. the mark has not moved at all, it's at the same position regardless of if I check it on the leading or trailing front wires. My guess is I have some combination of a clogged cat (checking this week) and poor timing, but I just cannot get the marks to line up properly. If anyone can give me any OTHER things to check that would help this motor feel it's pull power potential, and how to get past this bizarre timing problem, I would be extremely grateful as this car so badly wants and deserves to be quick.



Thank you in advance, looking forward to making some posts NOT begging for help in the future as I learn more about these cars
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Old 11-06-2005, 11:55 PM
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All stock intake manifolds?

You are still on OEM ECU correct? AFM included or ditched?

SAFC or something? If everything is "jiggy", inspect wiring to both coolant temp sensors, and the AIT sensor..



You'll have trouble setting timing properly if, the AFM along with all the other variables will affect the timing on the OEM computer, your SAFC is dinking around with the settings way out in left field, the timing will go for a dump too, the computer won't understand what's happening.



I had the same problem, at least for me after the car was "warmed up" the timing would reset to proper spec and the car would literally spring to life.



Other than that, it felt like it wanted to go but just wouldn't. Sometimes (depending on the motor temp), it would cool off enough to fall back into the whacked timing and it would have no power until a couple sets of lights down the road, then spring to life again.









But all things said, make sure you are using the correct method for setting the timing to begin with.
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Old 11-07-2005, 12:06 AM
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Thanks for the quick reply, I'm using the stock ECU and intake manifolds, but funny that you mentioned AFM (air/fuel mixture). I just had the car in for emissions last week and the way the tech got it to pass was by adjusting the a/f mixture screws on the passenger side of the engine bay, could that be a major point of concern?



By the way, the car seemed to have more low-end torque while operating cold, requiring more and more throttle to get moving as it warmed up.



I also advanced my timing as much as I could and the car seemed a lot peppier but still not as fast as my friend's stock manifold and port n/a.
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Old 11-07-2005, 02:07 AM
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that emissions buy probably leaned out your mixture



or something like that
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Old 11-07-2005, 04:07 AM
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I just had the car in for emissions last week and the way the tech got it to pass was by adjusting the a/f mixture screws on the passenger side of the engine bay, could that be a major point of concern?
That pot. only affects idle mixtures. I'm assuming the tech was having trouble with idle? BTW, where are you that the techs are fiddling with your car?



You may be on the right track about the cats. If they're plugged it will definitely feel boggy or sluggish.



Welcome to NP btw.

Cheers
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Old 11-07-2005, 08:39 AM
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That's the thing with the damn AFM influence on timing, it won't matter how good you SET the timing with the CAS, the AFM will still bump it around retard and advance when it's confused..



It was probably not a good idea to have dinked with the AFM...
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Old 11-07-2005, 06:53 PM
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Thanks for the welcome, pretty insightful opinions so far.

SO on the topic of the AFM, it was done during my emissions test on the rollers just to get me to pass and hasn't been adjusted since.

Would it be at all possible to find a resource or someone to hold my hand on how to adjust the AFM back without paying for dyno time?
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Old 11-07-2005, 08:39 PM
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turn it one way dramatically, go around the block, see what happens, worse or better, if its worse then you turned it the wrong way





not really gonna hurt it any more than it has been by running so lean.. sounds like its on the brink of stalling
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Old 11-07-2005, 09:04 PM
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I really think his "small cat" is the problem. It goes along with having less power when warm. A plugged cat will lower vacuum levels, maybe the ECU is picking that up as a load on the engine and compensating the timing? dunno.



I thought that variable resistor only affected idle mixture. I always tweaked it to reduce the burning eye effect of rich idle. I never noticed a change in drivability.
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