Strange power band problem on SOHC... >.<

prototype · Post by **prototype** » June 15th, 2005, 12:44 am

While during the day here in florida the temps are around 85-90 and the car runs rich and doesn't start pulling hard till 4k rpm. There's a significant difference when it hits 4k rpm too, like it's bogging down before then or something, and the car is just utterly slow as balls.

But at night time when temps are cooler, at around 65-70, she runs like a dream and pulls hard from idle to redline and I don't see any bits of black smoke coming from my exhaust pipe...

I've got a CAI and a muffler as far as mods go and I have been noticing my temperature gauge dropping down and twitching about like a connections lose or something... Or maybe a bad Temperature Sensor? And if so, the temp. Sensor also tells the computer how much fuel to add depending on if the car is cold and needs to be warmed and such right? Do you think this could be the problem? and if so, the coolant temp. sensor for the gauge and computer is the one located in the intake manifold, right?

Thanks in advance... I really need the advice, the sluggish day time driving is well driving me insane.

dj inferno · Post by **dj inferno** » June 15th, 2005, 2:47 am

umm i cant help you but... I HAVE THE SAME FREAKIN PROBLEM!!!! so will sumone else help us... i mean same... as every detail you said i got. my temp gadge goes to my music sumtimes... i dont think thats right....

prototype · Post by **prototype** » June 15th, 2005, 3:27 am

Yah when my amp is turned up I can see my gauge ticking up and down to the beat as well. I also noticed that if I hit a bump it will cause it to blip up and down, and also if I play with the throttle I can make it move about. I'm really most concerned about the power thing though. SOMEONE HELP PLEASE.

yiorta · Post by **yiorta** » June 15th, 2005, 4:24 am

Same problem on DOHC...

Yoda · Post by **Yoda** » June 15th, 2005, 11:31 pm

When I first bought my beater car with a 1.6 SOHC it was a real dog. There are several things that could be causing this. It sounds like your car is running to rich which is causing the engine to bog. As the air cools and becomes denser the night the air/ fuel ratio becomes closer to normal. The most likely cause of this is a bad O2 sensor that is not adjusting the fuel to the air density or it is just running in the default limp home mode and not adjusting at all. Another cause could be a weak electrical system. The first thing I do with every car I've owned for the past 25 years is improve the chassis ground. I also upgrades my main power cables from the alternator to the battery with a premium grade 1 gauge cable. A 6 or 4 gauge would have been good enough but I had tons of short 4-16 ft scraps laying around in the recycling box. You said you installed a CAI. The problem with almost every CAI I've ever seen on the Mazda B series engines is that they increase volume of air entering the engine to much. This makes the air very lazy and requires energy to pull the air into the cylinders on the other hand a smaller diameter pipe increases velocity The faster moving air tends to draw even more air through the intake and swirls the air into the cylinder creating a more effecent burn. A few years ago I replaces a friends intake with a 2.5" pipe on this BP-DE and thought I had done more that just change the intake pipe the power change was that dramatic. On my 1.6 SOHC the best results I've achieved on a dyno is with a 2.25". This in combination with my own exhaust design created an effect where I had the opposite problem and was running to lean when the air became denser. I had to fool one of the sensors to make the ECU run the engine richer.

prototype · Post by **prototype** » June 16th, 2005, 2:03 am

I was reading through a CEL code pdf and it said that in limp home mode the computer pretends like it's running at 67 degrees and runs air/fuel compliant with that, which seems to be like what my car is doing, but I don't have a light. Also I agree with the intake, it did shift the power band upwards a lot because it's so long I think it causes the engine to try hard to get the air flowing at first and then as the air starts moving and the intake valves close the air continues to move creating a vacume on the intake side and a pressure on the back of the valves, cause it's got a lot more kick when I shift the gears. And I've ran new ground wires already. I had a lot of 4 and 6 gauge lying around so I used the 6 gauge and regrounded all the stock grounds and then ran additional grounds to the battery and such. It evened out the idle a hell of a lot. So for a list of things to try...

1. Check CEL codes.
2. Clean O2 sensor, if it helps, then replace.
...
3. You got the car running too lean? Wow. I see why you are called Yoda. That's a lot of air going in and out compared to factory tohave that happen. Btw how much did you get your 1.6 SOHC up to on the dyno? I see people claiming 67whp after extensive modifications and I just can't believe that. With a 20% power train loss that means they are only putting out aroudn 80bhp. And I know that is far from correct. The SOHC can't be that bad, it's rated at 88bhp. Come on now..

And thanks for the help.

atlantamx3 · Post by **atlantamx3** » June 16th, 2005, 10:03 am

prototype wrote:I see people claiming 67whp after extensive modifications and I just can't believe that. With a 20% power train loss that means they are only putting out aroudn 80bhp. And I know that is far from correct. The SOHC can't be that bad, it's rated at 88bhp. Come on now..

Yep- that was me. Believe it.

1992 1.6L 16V SOHC Automatic MX-3 RS.

Here is my Dyno chart:

At the time I had an HKS filter adapter and a weaponR cone filter with an aftermarket muffler. Only other mods were to my suspension. Not really "extensive modifications".

However, it was an automatic as well and I am sure that robbed some power as well.

In Vaughn's 323 with the 1.6, he only had 8V which took more kindly to mods than the 16V or so he says.

prototype · Post by **prototype** » June 16th, 2005, 9:57 pm

I pulled my cel codes and got a code 34... ISC... = Idle Speed Control or in more common terms, Idle Air control. I remembered then that I had my ISC unplugged because it is broken and so I plugged it back in and for some reason the car didn't die at idle! So pleased, I took the car for a spin and it ran perfect... But then 20 minutes later, at a stop light it died, and after wards it just idled weird and kept dying on me, but it doesn't make weird power bands. lol.

Btw, that dyno is effed up! That's pitiful man, something must be wrong, either the ATX is just that much of a power hog or your motor had serius problems. I'm gonna have to get mine dyno tested after I get it fixed. If it comes up being less than 70whp then I will set my car on fire and buy a honda...

atlantamx3 · Post by **atlantamx3** » June 17th, 2005, 1:22 am

Whats really bad is it was running VERY nice that day. It felt really strong on the road and pulled as hard as ever.

prototype · Post by **prototype** » June 17th, 2005, 8:59 pm

I don't think the people that dyno'd your car did so correctly... Cause I mean, a 95 honda civic dynos at about 97 whp... which is only a few horses less than what the factory rates the bhp, and I notice that the graph doesn't start till 3500 rpm? and it ends at 6100rpm? Should start at 2k or something, and end at redline...

BTW Automatic trannys are very hard to dyno, you have to trick the car to stay in the gear that represents a 1:1 ratio and from what I've read about the mx-3 auto tranny it's not nearly as simple as a chevy th400. . . So I'm guessing that might be a problem too..

Is the car still an auto? If so, go dyno your BP. ^.^ If not, then dyno the BP anyway AT THE SAME PLACE. I smell something fishy.

Oh yes my car has gobs more power than before.. I stomped it at 45 in the rain in 2nd gear and did a burn out. Yayness. And if I click on the A/C button (even though my A/C does not work) then the car idles perfectly fine as long as the fans are turned on too.

What's up with this? Do you think just cleaning my ISC would help or is this a bigger problem?

atlantamx3 · Post by **atlantamx3** » June 17th, 2005, 9:35 pm

Well, I have confidence that it was dyno'd correctly. It was done at a "Dyno day" with the local Probe club. The dyno guy there was Ed Senf who is one of the leading dyno tuners in the nation.

Also- the redline on the RS is 6250- so I took it all the way to red line (or as high as it would let me take it w/o changing gears on me). It started so high in the rev range because I had to drop it a gear (mash the gas) and thats where the revs landed.

Anyway- I feel that is a pretty accurate dyno.

Tunes67 · Post by **Tunes67** » June 17th, 2005, 10:05 pm

He is right.. as a fellow ATX owner (even though I have the DOHC) My car is gutless unless I punch it hard and make it kick down completely to passing gear. Which of course is why the ATX is going bye bye before the end of summer. I havent dyno'd my car.. but.. I did spot a 95 RS at a local dealership a couple of months ago.. it was a 5 sp and was higher mileage than my car and it puffed smoke when shifting.. I test drove it (briefly considered trading my car for it) and that mx-3 would have sent my car (with a engine in great condition and tuned fairly decently) home with its tail between its back wheels

Bottom line.. ATX = Huge HP thief. Heck my 5 sp Subaru XT has more torque off the line than this car and it has almost 200k miles.

As Yoda said.. reduce the pipe size of your CAI.. maybe you can find a tapered pipe with a small inlet that slowly expands big enough to fit on your TB. Best of luck.

Tunes67

prototype · Post by **prototype** » June 18th, 2005, 11:58 pm

Alright, then I'm very happy to have my 5 spd.

I took apart my throttle body and cleaned the heck out of it and plugged everything up and the car is running near perfectly.. When the motor is cold and I start it up and turn on my fog lights and headlights, fan, and turn up my amp then the idle drops to 250, and the for the first 2 seconds after cranking it, the idle jumps a little bit around. However after driving it for a good few minutes, it idles fine, and screams like the little beast that it is.

I <3 my mazda.

Now I jsut need to get my A/F gauge hooked up so I can safely advance the timing for another horse or two.