Rough Idle and Bad MPG
 

Hi all,

Every rotary is built different, your first engine could have been capable of 18 city but the new one may only be 15. (fwiw my 8 get 15 city 20 highway)

as for the AC and rough idle, the AC and lights have a rather large steal from the engine but if the vibration is extremely bad check the engine mounts if those are good i'd say its normal


the hot start issue could be the dwell time with the bhr ignition a tune would fix this

[QUOTE=sonicsdaman;4630366]Every rotary is built different, your first engine could have been capable of 18 city but the new one may only be 15. (fwiw my 8 get 15 city 20 highway)

Get your alternator tested. A few of your symptoms are in line with an alternator problem resulting in voltage/output fluctuation, which in turn can cause spark and fueling problems as well.

In case that isn't it, disconnect and thoroughly clean all your major grounding points, since grounding point corrosion can also cause voltage fluctuation.

You would have kept the same alternator from your old engine to the new, it is just transfered over.

Also check to be sure that all pulleys are spinning freely. You will have to remove the belts to test this by hand. If any of them have resistance or grinding or lumpy motion, that could contribute to your problems.

I suspect that all your normal mileage related parts are fine, because of the highway mileage. When everything is stable and the fans aren't needed, your mileage is predictable. It's city mileage that is the problem, which means something is soaking engine power more than you normally expect. I'm going to assume this isn't a change in driving habits, even from external sources like thicker average traffic or an extra light, or a change in light timing that means you sit at lights more. The fact that you have symptoms that point to a voltage or current control problem tells me that there is a real issue there, even excluding outside factors.

City driving will have much more fan activations and a wider range of RPM usage, both of which challenge the alternator more. Even a slight problem there could easily have a noticeable impact in gas mileage.

Remans will have lower starting compression, it takes time and mileage to wear in the engine back to where it should be for a 'new' engine.

If it is the car that shakes at idle, but the needle is stable, then yes, it's likely a motor mount problem. If the needle is what isn't stable, regardless of whether or not the car is physically shaking, then there is another problem that has nothing to do with motor mounts. If you fix that and the car still shakes physically at idle, then yes, motor mounts too.





(Remember to get your coolant system flushed between 3,000 and 5,000 miles after the reman change, to ensure you don't have a cooling system failure from the excess sealant Mazda uses on the reman builds)

Listen to riwwp he's better at this then me :lol:

Thanks!!

Can I test the alternator with a multimeter at home? Just monitor battery voltage while I start the car and rev it some? Or is it better to have it tested professionally somewhere?

The idle shaking corresponds to the RPM needle dipping, it's not just shaking with stable idle. That suggests it's not (or not only) the motor mounts?

You're all better at it than me! :lol2: These forums have been a life saver many many times.

Test it professionally. Most auto parts stores can do it for you, though some aren't willing to test it on the car, some can't test it off the car. I'd expect most privately owned shops can do it too. It's more than just the output voltage.

However, that being said, if you test the output voltage with a multimeter while it's idling, and it ISN'T stable, or is outside the ideal range (~13.2 - 14.9v), then you have confirmed the core issue. The next steps would be to fine out if it's because of an alternator failure or because of a poor electrical connection somewhere. Both will still be possible without a professional test of the alternator.

Yes, if the needle is dipping with the shake, it's not the motor mounts that is doing that. Put another way, the motor mounts can't possibly make the idle speed change :)

So the output voltage was stable at 14.3 when idling. I went around and loosened/tightened all of the ground contacts which might have improved idle smoothness; I'll keep an eye on it when I drive more later.

Now that I was looking more closely at the alternator, the belt on there looks to be in pretty bad shape (frayed edges). Do they not replace belts when they switch out an engine? The belt felt tight enough, just didn't look great:

Alternator Belt - Imgur

Time to order one of those and replace it? I can check pulleys then too.

Yeah, replace them. Whatever your local auto parts store has works fine. OEM ones from a dealer are around $60 i believe, including markup.

Interestingly, that could also contribute to your problem. It's rare, but possible. When I had my 99 Miata, I apparently clipped one of the belts when installing the 2nd engine (it went through more engines than my 8 did), and frayed. The frayed bit has metal in it, and it was hitting the crankshaft sensor (same function as the e-shaft sensor), and disrupting the magnetic signature periodically when it would hit at exactly the wrong time and crank position. Took me a bit to figure that one out.

Ouch, that sounds like a tough one, that intermittent stuff is frustrating. My Subaru started having it's AC clutch stick open every once in a while depending on how large a bump I drove over. That, combined with some funny wiring, was a real chore to narrow down.

Okay going to try and pick up some belts and throw them on tonight. We'll see how late the auto parts place is open.

Changed out my belts this morning and had everything running. Went to tighten down the last bolt on the AC belt, the wrench slipped off, and totally destroyed my VFAD solenoid. Arghhh.

Anyone know a good place to pick up a VFAD solenoid?

Oh, and all the pulleys spin freely.

Ouch, sucks :(

On to testing the alternator and disconnecting/cleaning grounding points.

One of the partout threads over in classifieds is probably going to be the cheapest replacement solenoid, otherwise, contact Mazmart.

i think i have one in my garage

That's not attached to your car? :lol2:

If you want to get it out of your garage I'd be happy to buy it from you, but it looks like Arlington and Ebay could get it to me too:

Arlington

Ebay

Oh, and here's mine:

Very Sad

yep almost positive i have one. ill check when i get home

Short term, just disconnect the line towards the VAFD actuator, disconnect the wire, and plug the vacuum line. I think the default is open for the actuator and the vacuum closes it.

Great, thanks. That should make it drive-able until I get the solenoid?

I've got another vehicle to use for now, but just in case it would be good to have the option.

I actually have that line capped off, the wire connected to the dummy port on the air box, and the VAFD in a box in the garage.

Reduced intake temps a rather large amount (like 15F) when I pulled it out.

The silent portion is a tube that runs across the top of the radiator, it makes a great air charge heater.

Interesting. Are you running a lot of other aftermarket parts? Are there any drawbacks to doing this on an otherwise stock engine? I'd imagine they put it in there for a reason, right?

my vfad is in the garage too. i do have a bunch of mods but it doesnt matter. its there to keep noise down at low rpm iirc. you can cap it under the throttle body

Great, thanks for the info. I'm not opposed to forcing some more rotary noise on the people around me.

Okay I pulled the alternator this afternoon and took it to get checked. The guy at the auto parts store ran the test three times, and it checked out just fine. I had some 4awg wire sitting around at work, so I made a grounding kit as long as I had everything pulled out. I followed this guide:

DIY Grounding Kit

I didn't have enough wire to make the link across the back of the engine bay (through the cowling) or the wire from the battery negative terminal down to the bolt under the airbox (there's already a wire there). While doing that, I used a dremel with a wire brush to clean up all of the ground contacts.

If anything the throttle seems more responsive and power feels more immediate, but it's hard to tell if that's just placebo effect because I've been wrenching on her all day! Idle still has it's small quirks where RPMs will drop and the car will shake slightly. Maybe the ECU is still trimming in? I'll keep an eye on it and see how gas mileage does.

Beer time. :beer:

Sounds like you did well.

I have started to believe that the ground are a big issue (did you notice that you were cleaning paint of the grounding surface) and a kit, or at least star washers, really help. All of my lines terminate at the bolt under the air box, and then one line runs up to the battery. That makes things look cleaner.

I think I have the intake manifold area bolt attached to the one in front of the oil filter (PITA) then to either the Coil bracket. Coil bracket is close to the compressor, so that is good. Coils are a good source of noise. Just make sure you have a big wire running to the battery.

And, likely things are improved. On mine, the idle when smoother almost immediately. You have not reduced a ton of noise from the sensor lines and that is how the ECU runs the engine. There is a different DIY in the Congrats thread below, but it is much the same as you did.

You might want to look at the rest of the $100 items as well. Those are things that made my life easier.