Car stumbles intermitently around 3k, 4k, 5k. I haven't changed anything so I'm wondering why it's stumbling. It was working the last time I parked. Started driving it, notice that it stumbles heavily underload and am usually unable to rev past 5k. Will sometimes stumble at 3k, other times 4k, and still other times it won't start stumbling till 5k. The intermitedness of it tends make me think that it's electrical. Should I add the extra grounds? Or is there another possible problem. I noticed that my pressure sensor hose was extremely loose--I fixed that, but still suffer the same problems.

Concurrent problem with the car: Intermitent Hardstarting/flooding.

 

I would start by checking ground connections. Aaron Cake has a good writeup on this topic if you search. Also do a maintenence tune up (plugs, plug wires, fuel filter, etc.) if it hasn't been done in the last 30k or so.

 

I replaced the spark plugs with brand new NGK's... stumbles now between 2-3k. Still has cold start problems. But if I just turn it off and come back out within 10 minutes or so, it starts up fine.... Also I don't know if this might be an indicator of anything but the right turn single blinks hella fast, but both bulbs are fine and work.

 

A video of the car being driven would be helpful, perhaps with a window down so we can hear the exhaust note. This would help us try to determine if it were an ignition problem or fuel-related.

 

I'll try to get you a video tomorrow. It's too dark out and the lights don't let my camera pick up the needle.

Another problem that might be causing the trouble: Only 1 6PI is working. But that's been like that for awhile and never had a problem before.

 

Try running some fuel injector cleaner.
Do you still have the precats? If so get rid of them.
You should do the custom grounding setup. Its just helping out the electrical. Easy thing to do is to run a ground wire from you alternator bolt to the - battery terminal. Make sure you - grounds are connected 1 next to the upper rad cap. The other is above the exhaust bolted to the firewall + make sure that this wire is bolted to the tranny.

 

Fuel injector cleaner is pretty much useless. If they're gunked up enough to cause it to run bad, then nothing short of removing them and getting them professionally cleaned will help.

 

I'm starting to think it's a problem with the fuel. In my mind the engine isn't getting enough fuel... whether that's from the injectors not being grounded properly--which I've checked they are--or from them being clogged I don't know. If they're clogged that would explain my hardstarts when the engine is cold (but not why it starts when the engine is still warm). I picked up some heavy gauge wire for free, so I may invest in some crimps for it.

I've checked Aaron Cakes write up on grounding, and tomorrow I'm going to dig into the engine and remove the upper manifold and check out the harness. It just seems odd that the engine would suddenly start these symptoms.

 

Check your compression, actually. When my motor starting going out it kinda acted like this, but then again I have never seen an engine die quite the way mine did....
Get a piston tester, and hold down the release valve while a friend cranks the engine. You should get even pulses, preferably at least in the 90-95 range. Post the results here.

Another major thing to check is the grounding to the coils. I hadn't tightened down my coils well enough, and had some major hesitation.

 

Already tested compression. I was around 85-90 on both rotors. Didn't do the pulses though, but for the most part they hit that pretty quickly on the cranking. I didn't check the grounding to the coils though. I'll do that first tomorrow morning.

 

Checked and cleaned the grounds on the coils--didn't help
Took video of symptoms from 1st-3rd (I think) keeping my foot in the same location and not adjusting it up and down from the partial throttle. You'll notice the rpm stall and not really move around 4-5k which is where the stumbling was hitting pretty hard.

Here's the video:

Sorry I didn't have more, but that's the best I could do with what I had.

I've picked up the stuff to make the grounds, and I'll probably do that once the engine cools down enough for me to remove the Upper Intake Manifold.

 

Okay, so I ripped into the engine and removed the upperintake manifold. Cleaned up the ECU ground on the engine, made a new ground out of 2ga I had around and attached it to the driver side strut.

While I was there I freed up all my 6PI's and they now function.

The outcome of all this:

Car can now start cold without problem, still stumbles between 3k-5k. Perhaps the grounds for the coils need a little help? Where would I attach the extra ground and where would I anchor it to (Back on the driverside strut again)?

 

New symptom:
It now does it while not under load. Revs well from 1-2k, then from 2.5-5k stumbles all over itself, then usually revs fine from 5-7k.

 

You can also connect a ground wire to the battery - post. I'm not sure this will help your problem but it can't hurt.

Have you removed the cats?
Also check the connection at the thermowax. I had cold idle issue's and found the my connector was not connecting all the way. The small pins were pushed back some how and were not contacting. Small steps

 

That's my ultimate goal (I made the two gauge long enough to connect) I just need to pick up a new battery terminal for my negative. I'll then be able to connect it to the battery.

I've already noticed some difference in the ground I made. The starter spins faster, and I get warning lights when I put the key to on but don't turn it over. They go away once the engine is running. That's what's supposed to happen right?
No, I don't have the resources at the moment to replace the cats with anything else.
I'm not sure what you're referencing with the small pins. I highly doubt that's the source of my problem since idling is fine, it's just starting and the stumble which seem coincidental (on top of that the pecuiliar right hand turn signal blinking twice as fast as normal even though the lights both function).

Tomorrow I'm planning on picking up a fuel pressure gauge from advanced and putting it on to see what the fuel pressure is reading. I'll probably also replace the fuel filter while I'm there because I have a nagging suspescion that the filter has not been replaced in the life of the car (it's an 86).

 

Ok when you do get a chance hollow out the first 2 precats. I've done it to every 7 i've owned. It will not effect the smog test and could be part of your problem! Leave the main cat alone! The first 2 precats are there to keep emm low during warm up. It was the only way mazda could bring the car to the states. Just use some rust buster on the bolts and take of the cats. Then hollow them out with a big screwdriver. Make sure you get out all of the comb stuff. This will cost you nothing but time and could be part of your problem.

I just did my grounding set up last week. I ran a wire from the alt-front cover-first housing-secondhousing and so on. They run in sequence(they are all connected in line). I then ran a wire to the firewall and another to the battery.

Change the fuel filter as well. That could cause some of your symptoms. I'd recomend factory.

Thermowax can cause startup issue's I think. But I'm not sure. I still have startup issue's on my TII and am trying to figure out what it is. Starts perfect when warm but hard to start when cold! I have to give it gas for about 20 seconds then it will idle. I messed the connections at the thermowax ( maybe I'm confused it's the peice on the uim with the idle screw)and it started up fine. I think the connedtion came lose again though. I'll look later tonight.

 

The only way I see that being a cause of this problem is if a massive chunk of carbon got pushed out the exhaust port... but even then it just doesn't seem likely--but I'll try to tackle that tomorrow.
When you turn your key to ON but don't crank do all your warning lights and shift light light up?
I'm definatly doing that tomorrow.
Thermowax is only to keep the revs down when the car is warming up--I'm not sure what you're refering to when you are talking about pins... Got a picture?

Also not sure if this a symptom or not: but I've modded my 6PI to run off the air pump (the only thing the air pump is doing). I was under the impression that they should still kick in at the stock rpm (3800). However when I was getting my friend to check they weren't fully engaging until around 5-6k right when the stumble goes away.... hmmm...

 

they won't engage unless under load at 3800, so you have to remove the vacume line from the pressure sensor on the passenger side by the air box, and hook it up to the UIM to get a full vac reading on the sensor, then they should work will not driving, just make sure to put it back when done (vac line)

 

Huh? It's an S4. It goes by back pressure which I've altered to run off the Air Pump which delivers the necessary amount at 3800 rpm. Unless I'm reading something wrong and the acv causes the actuators to move using a vacuum... Maybe my brains not working right now. I've been up too long.

 

How well does the engine run under hard acceleration, with foot to the floor?...if you have fuel supply problems, such as fuel filter or fuel pump, it tends to show up often under this type of driving.

When I listened to your video, it sounded a bit as if it were running rich in those areas, perhaps from a skewed coolant temp sensor or corroded connector, or other possibilities such as fuel pressure regulator, glitchy AFM, etc. I have also seen a few pressure sensors with glitches in the signal at various rpms, and I have verified it with a timing light (erratic spark advance) and then confirmed it with a lab scope connected to the signal wire. Sorry for all the rambling......I realize most people don't have lab scopes sitting around, but it is the best way to capture signal glitches, followed by multimeter testing.

 

oh my bad, must have missed that, didn't know you were running the altered setup there, or just slipped my mind as i was typing...

 

It does the same thing. Just when I do get past the stumble it's ***** to the wall all at once. So basically the Tach reads really quick climb from 1-2k then stumble at 3-5.5k then quickly hit red line and it's time to shift.
I don't have a lab scope here (but I did have a few a few years ago). Could you give me a list of things I should check out (most likely to least likely)? If I'm running rich in those spots and it's related to engine temp then I'd think it's more of a screwed up coolant temp sensor. Are you talking about the one on the radiator?

 

The coolant temp sensor I'm referring to is the one on the water pump housing under the alternator. The ECU relies on this sensor rather heavily to determine which part of the fuel map to execute under all temperature conditions. It is the equivalent to a "choke" on a carburetor, giving a richer fuel mix that a cold engine requires, and a progressively leaner mix as the engine warms up. It's not uncommon for the sensor values to "skew" from the original specs as a result of several years of thermal cycling. For example, it is possible to have correct resistance specs within a certain temperature range, and completely out-of-spec values at a different temp range. Corrosion at the connector is somewhat common as well. I can give you a list of what to check with a lab scope or multimeter and which wires to backprobe when I get back home from work. Basically, as with any mechanical variable-signal sensor, you want to see consistent linearity of each signal, for example with a "flap" AFM, you want to see smooth sweep transitions as you open and close the flap, preferably using a lab scope, but an analog multimeter can be used instead, with somewhat less glitch-capture ability. I'm off to work.

 

I'm going to break up your post into a list for me to check and comment (for myself and others)
Okay, I went outside and did a once over on the car and saw the plug you're talking about. I felt kind of foolish once I saw that because the sensor I was thinking about was the low coolant level sensor. I'll get the plug off and double check for corrosion. If that looks good how do I test the sensor? Do I check resistence? Do I do this while the car is on or just when it's warm?
Please do. I was hoping to be underway today for a 2-300 mile instate road trip. But if I can't get this problem figured out I don't exactly know what I'll do.

I went by a local RX7 Guru for advice and he thought it might be my TPS--I double checked it and set it to 1v again, and checked the voltage range... it didn't suddenly drop voltage when I was checking it, but then again the problem is very intermitent. The only other advice he gave me was to pull the kick panel and re-do the grounds for the ecu.

I went and drove the car for a few minutes and for about 10 minutes at temperature there was no stumble. Then when I thought the car had fixed itself like it has done on previous occasions it started bucking and stumbling all over itself.

 

oops...just read your tps post. but does this happen when the motor is cold or hot? i ask because one time i took a 120mi. trip. turned it off, turned on the car after 15 min., then wouldnt start. so after push starting it everything was fine but it wouldnt rev past 2k rpms (tps). so after an hour of cool time started it up and it "fixed" itself. that only happened once though cuz after i got home. ii never happened again.