13brv3

Greetings,

I just had a productive weekend with the car. I managed to change the oil (Valvoline 10W-30), trans (RP), and Diff (RP) fluids. I also changed the fuel filter (oh joy), plugs, and plug wires. Unfortunately, it didn't fix the current problem.

When I got the car a couple months ago, it didn't have more than 5 psi of boost above 4500 RPM. This was fixed with a hose job. Now that I have 10 psi of boost (trailing to 7 at redline), I have a light to moderate hesitation that starts around 5500 rpm and lasts till redline. This feels like the power sags, then comes back, over and over, getting worse as RPM increases. I barely notice it in 2nd, but it's there in 3rd. This hesitation was NOT there before I picked up full boost, and I hoped the plugs, wires, or fuel filter would take care of it, but no joy.

The car is completely stock, with 84k miles (only 9K on the engine). I'm trying to get everything working corectly before I start modding it. Here are the things I've read, or thought of myself.

Grounding- The car had a horrible light throttle bucking when I first got it. Once I cleaned up all the engine bay grounds, the problem was gone, and hasn't returned. I do know that the exhaust grounds are in place, but I have not attempted to clean them. I have also not added any additional grounds. If you suggest additional grounds, please specify where you'd put them.

Injectors- I ran a bottle of injector cleaner through the system to see if that would make any difference, but it didn't . Is there any way to confirm that an injector is misbehaving, without removing it to have it tested? Will you get a check engine light if one gets too screwed up?

Boost leaks- I don't see the boost gauge fluctuating along with the power fluctuations, but I haven't completely ruled this out.

Plugged pre-cat, or main cat- I'm not quite sure what the symptom of a plugged cat is. Could this be my problem? It is only high RPM, and high power output.

Thanks for reading though this, and giving it some thought. If you have any suggestions or comments, I'll be most happy to hear them.

Thanks,

Wade

iTrader: (1)

Make sure your plug wires are on correctly. You might have a bad leading coil. It sounds like a misfire.

How quickly does the power go away? Is it for a split second each time, like the engine is missing, or is it for longer, like a second? Approximately how many times does it hesitate from 5500 RPM up?

You could check your fuel pressure by tapping into the pressure line near the firewall. If it is okay, you are probably getting plenty of fuel and your problem is most likely ignition related.

Wade

13brv3

Wade,

Plug wires are correct, and I agree that it sounds like a misfire. I figured the plugs and wires would take care of it.

The power loss is just a momentary thing, way less than a second. I'd guess that happens maybe 6-8 times from 5500 to 7000 in 3rd gear.

Sure wish I had though to put an ohm meter on those coils when I had access to them. Not sure that would really tell me much though.

I've also read about overly rich mixtures that couldn't be fired by the stock ignition. Any thoughts on that?

Thanks,

rxrotary2_7

in 93 the harness for the coils had a ground that would cause an arc. this was changed and you can now get the "new" stock harness without that ground. it is only like $35. i would try that first.

13brv3

Just to be clear, are you saying that if I order this from Mazda now, I'll get the later, better version?

Thanks,

rxrotary2_7

i think so. i had to look it up when i ordered mine. the dealer had NO IDEA what i was talking about, but when i gave them the part number, they just said "oh the coil harness..." so i am guessing that is the only harness available now.

edv

I had a similar problem with my stock 93..a noticable lag in thrust at the point where the 2nd turbo comes on stream. I had the luxury of warranty coverage at the time (exactly 1 year ago), so I had the dealer (Ack!) check all the hoses, etc. Found nothing wrong. So, the day after the warranty expired I installed a Downpipe. That went a Looong way to resolving the problem.
So...my simple advice to you is to just install the Downpipe. You will be happy. You will also then be able to discern where to put the bung & sensor when the time comes.
BTW, my pre-cat's biscuit looked pretty fused upon removal. Really glad I replaced it.

Rated R1

Which plug wires are you using?

13brv3

Thanks for all the comments.

Rated R1- the wires are stock Mazda from Mazdaformance.

edv- I don't think I have the exact problem, but if I don't find another cause, the DP will certainly be the next thing I try.

rxrotary2_7- Thanks for the followup. I'm getting pretty tired of pulling the top of my engine apart every weekend, so If I change that harness, I'll probably change the coils too. I understand they're pretty expensive new, though I don't know quite how much they run.

Cheers,

Mahjik

iTrader: (1)

The coils aren't too expensive:

http://www.mazdatrix.com/ign-1.htm

The igniter is a different story.

13brv3

Ack!!! I forgot about the igniter

Hmmm, before I'd consider buying one of those, I'd be looking at aftermarket ignitions. I know the stock unit is pretty good though. I'm starting to think I need a parts car

Thanks,

FDjunkie

I've not (yet) experienced any similar problems with my '95 PEP, but its still has less than 68K miles on original engine, etc.

However, I did a search and found this thread that has details and pictures on the coil ground wire issue already posted.

https://www.rx7club.com/forum/showth...threadid=70779

13brv3

Thanks for the pointer. I made a note earlier to try searching for ignition stuff, but hadn't got a chance to do it yet.

I'm still curious to know just what this ground does, and what actually arcs. The ignition signal on that cable should be low voltage, so I don't see how it has much potential to arc to ground. If I end up replacing the harness, I'll disect the old one.

Thanks,

neevosh

I'm having the same problem. After 5500 RPM's I'm having some ignition misfire. Hopefully just my plugs are fouled. I was running extremely rich. I'm interested in your solution as I might be going down the same road.

13brv3

After thinking about this some more, I realized that there's a chance I damaged the old hardened coil harness when I moved it out of the way for the hose job. That might be what set it off, and not really the extra boost.

While thinking about this, I've started to consider changing the coils and harness. This will cost more than $400, so I wondered if there are aftermarket coils that I should also be considering. Any recomendations for aftermarket coils, or should I just stay with stock?

Also, if I test the coils per the manual, is that really a good test. In other words, what are the chances that they will test good, and still have functional problems?

Thanks,
Rusty

P'cola FD

Rusty, If you want, we can put Brad's coils, harness, and wires on your car (since his engine is out right now) and see if that corrects the problem. I wouldn't recommend buying stock coils. Gordon Monsen is running MSD ignition, and it seems to be working quite well. If your coils are the problem, I can give you his contact info.

rxrotary2_7

this is the kinda stuff you should always do in trouble shooting. use a "know" good part from anoher person BEFORE buying something.

P'cola FD

That's what's nice about having a rotary "community" where people can help each other out and whatnot.

13brv3

Thanks for the interesting offer Danny. I'll have to think about it some. The downside is having to take things apart multiple times with the loaner parts. I'd probably rather do it once, with new parts, or with good used parts that I own, so I can leave them installed.

Unfortunately, everything is on hold at the moment, for one of those family emergencies we dread all our lives

BTW- Another Red FD sighting today in Pensacola. I couldn't see the hood, but the car was heading South on Davis at about 2:30 with the sunroof open. You can run, but I'll find you one day Danny

Thanks,

LongRX7

iTrader: (12)

I had that problem at higher RPM's during WOT down the dragstrip. Installed a Jacobs Rotary Pro Pak from Rotary Performance and it solved that problem. Hope that helps...

P'cola FD

That was probably me you saw today.
The best part about the coils is that the only thing you need to disconnect is the plug wires and the coil harness to wiring harness plug. It takes all of 10 minutes to test.

13brv3

LongRX7- I looked up the Jacobs Rotary Pro Pak, and it looks to be only the controller. Do you get coils with it too, or are you using stock coils? Thanks.

Danny- 10 minutes??? What kind of pit crew are you running? It might be worth trying the coils so you can show me how you do that When my current family crisis settles down, I'll let you know if I want to test those coils. Thanks again.

Wade

iTrader: (1)

Yes too rich of a mixture can cause misfire but with a stock car that shouldn't be happening.

I'd try a new coil harness and if that doesn't work, swap the coils with known good ones as a test.

Wade

13brv3

Thanks for all the comments, but I'm not sure I have any less options than when I started

I'm fairly convinced that it's an ignition miss, and it's not the plugs or wires. That leaves the coils, the harness, or the need to get something like the HKS Twinpower amp. Once I started searching for "ignition miss", I found a few people that had the exact same problem, that were fixed by installing an HKS (or other aftermarked controller).

Of course it could also be that the stock ignition is working fine, and the mixture is just too rich for some reason, (leaking injector, plugged up cat, etc).

I have no idea what I'll try first, and I'm almost sorrry I asked

Thanks,
Rusty

P'cola FD

Yeah, all we do is hook up the plug wires, and the ignition harness, and let it sit next to the elbow. Ghetto fabulous. Just holler at me when you're ready.