Gurus: Help with really odd fisfire
 

Oh mighty RX7 forum gurus,

My 94 R2 has a problem. This problem occurs when the car is stopped and out of gear. As I rev the motor, the engine speed rises until it hits about 5500 RPM. Then, the engine hesitates, stuck at that RPM. As I apply additional throttle, the engine refuses to rev higher until a certain point (I'm still pressing the accelerator slowly more and more) when it breaks free and begins to rev up again to redline.

This problem is worse when the car is cold; the revs get to about 3000 before this hesitation starts. As the car warms up, the hesitation moves up the rev range.

When listening to the car, it sounds like the ignition is severely breaking up (B-R-R-R instead RRRRRR) and stumbling.

This problem has been around since I bought the car early last year. Since then, I have replaced:

* plugs
* wires
* leading coil

To no effect. I am still looking at the trailing coils and the ignighter, but I am not optimistic that this will fix the problem. If you have EVER experienced something like this and have some ideas for me, I would greatly appreciate it! Help!

-ch

Have you checked all the ground wires?
Make sure that all the ground wires are securely fastened.

Yeah, I made sure everything was connected and added two extra-big wires from the PS pump and the UIM. Is there a ground location that I should check that would most affect this kind of issue?

-ch

There are three main ground locations: one on the fire wall just behind the UIM on the passenger side of the vehicle, one on the driver's side fender beneath a black boxfull of relays, and one down below on the driver's side of the engine just above the lip of the oil pan. You need to scuff the metal behind the ground contact and the contact itself bare.

Yep, I replaced the UIM with a 4-gauge wire and used cooper conducting paste to help ground. I cleaned the one by the oil pan and used paste there as well. The connection under the fuse box looked fine to me but I added another from the PS pump to a bolt near the strut tower.

I think I'm grounded pretty well, but I can recheck things.

Any other ideas?

-ch

No ideas, but a question. Why the hell are you revving your car to 5500 rpm in neutral, and especially when the engine is cold?

If it doesn't do this when it's in gear, what does it matter?

Ha, good question. The problem isn't at 5500 when it's cold, it's around 3000. And I don't do it when it's stone cold, but after about a minute. At that point the oil's viscosity is low enough to flow (especially if you run a synthetic) so I don't anticipate any issues.

Also, this problem does occur in gear as well, but only at light engine loads (like creeping up on 5500 in 1st gear).

The reason I'm interested is that this symptom may be indicative of other problems in the system. For instance, I've tuned the car very carefully but still get lots of backfiring even though I'm running a HF cat. (I'm retaining the air pump for smog issues.) This probably isn't related, but rule #1 is fix the things that are obviously broken first. I just don't like the idea of the car behaving badly because you never know when the issue will occur in a high-load situation, and I don't know what other systems it may be affecting.

I guess what I'm saying is that there's clearly something wrong and I want to make sure it's fixed.

-ch

what's your a/f at idle?

Might want to replace your O2 sensor also.

pfc or haltech? or other...

Im guessing this is your problem, my backfire/misfire were all due to improper tuning. All better now tho :)

before i went stand alone EMS, i had problems with my coolant temp sensor that could never be explained. i did a temp fix w/ a POT to tricj\k the ecu into thinking the temp was different than it actualy was. it was a *bandaid*, but it worked. i spent over 6 month trying to figure the problem out with no luck. i wont even get into the list of things replace or tried. your head will smoke. but the $1.00 adjustable POT did the trick. maybe i am way off on your problem, but i feel your pain.

What city are you in and what ECU do you have?

Thanks for all the responses, guys.

jspecracer7: My AFR's are between 11.0-12.0 as I rev the motor. Please see the attached image which shows a plot while I am stationary, out of gear, and reving the motor. The top red line is RPM, the top blue line is the TPS. You can see that I am progressively opening the throttle, but the car gets stuck at about 5400 RPM. (The bottom blue line is vacuum which also rises with the throttle, but the revs won't go higher.) The AFR starts at about 12:1 and drops to 11:1 as the problem starts. You can see that after some point the throttle opens enough the revs suddenly shoot up, and then I close the throttle. Also, as you can see the injector map is constant throughout.

Toadman: I'm thinking about it, but I've checked the sensor and it appears to be completely within specifications. The problem doesn't go away when I disable O2 functions in the ECU software, either.

XSTransAM: I'm running a PFC. I have a wide-band and I've tuned the car pretty well myself. However, I've tried other people's maps (with similar mods to myself) to no effect.

rxrotary2_7: Thanks for the support. There are so many issues with this motor I'm actually thinking it will be less expensive and frustrating to just buy a new one. :)

SChan415: I'm in Mountain View, and I've got a PFC that I bought a little less than a year ago. I've also swapped ECUs with another PFC owner to no effect.

-ch

bumping to see if the problem was identified and fixed. i think i'm having the same problem.

Just generated this problem after bringing the vehicle out of storage. Feels like I stab the brakes when sweeping throught the rpms. ~3400 rpm @ 3psi.

Anybody found a definitive solution to this problem?

I have this issue at WOT, and anywhere around 5-10 psi... I've Replaced / swappend to check, just about everything.. (No Joke) Engine, Rad, Ic, Coils, ECU, Airpump, Igniter, going non seq. I even had the turbos appart while the engine was rebuilt, and the turbos looked good... but what I'm guessing it is now, is the turbos have either some play, or some imbalance in the shaft, that causes the bog, once it frees itself, it's fine again... maybe check how much boost you're making on a gauge, when this happens... mine is all over the place once it starts bucking and "Acting up"
I won't know for sure untill my GT35/40 comes in and gets installed, but like I said I've been chasing this for 2 months, with the help of a very good rotary mechanic, and that's our last resort... if it's not that, then it was a poor rebuild... the funny thing was the turbos acted up before the rebuld, we attributed it to a clogged cat @ 8 psi of backpressure... Since then we took the cats off to test, and no difference...

>>DCrosby

have you notice any diffrence yet or do you still have the same hesitation?

//Rick

Check you trigger wheel. Make sure that it isn't bent up too badly. Also, make sure that your crank angle sensors are within limit (1-2mm away from trigger wheel).

has anyone looked at the values in their tps's. watch it to make sure that they swing nice and smooth as you slowly open the throttle. sometimes it will have a bad spot on the rheostat and give a wrong reading.

I had a "customer" car that had a similar problem. It would really NOT want to rev over 4500-5000rpm. If pushed it would sort of push through it and then continue to redline with not much power. Low rev power was great.

The car would do this in every gear and in neutral, the check engine light would flicker but no codes were stored nor could they be captured.

I tore the entire top of the motor apart, checked all solenoids, injectors, vacuum diaphragms, etc. It all checked out just fine.

Finally I got to looking at the crank angle sensors, the wiring for the top/faster speed sensor was partially pulled out of the plug and there were only 2-3 strands of wire left on it.

Since the engine harness was sorta crispy and I had the entire freakin' thing torn apart I bought a NEW engine harness and the problem was GONE...

Please elaborate.

I was doing the tps adjustment on my car, and there were times when I didn't get good numbers or they would act funky for a couple seconds. I figured it was a poor connection either in my multimeter probes or the safety pin (I wish I had 3 hands - one to hold each multimeter lead, and one to move the throttle).

My symptoms (now that the car is running) is bad misfiring / bucking in general when I exceed 0psi.

Oh, and I did have some rev 'sticking' where it wouldn't fall immediately back to idle.

Dave