I don't have the 3000 RPM hesitation problems..actually I dont have any of the problems the Rx7 Bitches whine about on this forum, but I have to say you get my vote for "Forum Member Of The Year". You seem to figure all this stuff out.

just like to add that -
I installed a Stage 3 Pettit ECU 3 weeks ago. but, My 3k Hesistation remained the same. However I can remember the previous owner of the chipped ECU stating they did not have the 3k hesitation problem with the same ECU.
so Ill go do the bulb test for ya and let you know what happens.

So far we are still not sure if my idea is bunk ;)

Easiest way to test this is to bypass the fuel pump resistor and see if the hesitation goes away.

About cover8's post...

He was saying isolated lines and individual pumps for each injector. I'm sure managing that would be fun...
:D

Here's a question...and maybe I'm way off base.

The pump is putting out X PSI of pressure at a given speed, which I imagine is more than what is required. The pressure regulator will adjust accordingly to ensure that not too much or too little is supplied to the injectors. If you do the 12V mod and get it running full speed constantly, why wouldn't that just take care of the problem, no questions asked? The pressure to the primaries shouldn't change and when the secondaries come online there wouldn't be a drop in pressure from pump lag. At this point, I'd imagine that it's up to the regulator to ensure that the pressure ahead of it is maintained.

I hope that made sense...

I think I have asked this before, but I'll try again.

Does anyone with a fuel pressure gauge notice any irregularities when the hesitation occurs?

If the weather cooperates this weekend, maybe I'll give it a shot.

Did anyone figure out if this fix works? I am looking at buy a fd that has the problem and would like to know if I can fix it. Any help would be great. Thanks.

I have a 93 CYM with 126,000 miles. I bought the car in Nov of 94 with 18,000 miles on the clock. It has always had a slight hesitation at 3000 rpm when cold. Once it warms up it never does it again. I also have a friend with a 93 CYM that was built within two months of my car. His car has had a severe case of the hesitation from the get go. As a last ditch effort to fix the problem we took my ecm and installed it in his car for a simple test. With my ecu his car performed exactly like mine. It would only hesitate slightly when cold. He immediatly started looking for another ecu for his car. He struck gold on his first attempt with installing another used ecu. No more hesitiation.

All this leads me to believe that it has something to do with the ecu's.

I hope this helps

Wayne Mann

One of the aspects of this problem that makes it so "fun" is that you can't take any one person's experience and assume that it applies to everyone who experiences the hesitation. They symptoms themselves are pretty consistent, but there have been any number of things that have fixed or at least improved it for different people. Switching ECUs...even to Pettit-style reprogrammed ECUs...does not usually fix the problem, although clearly there have been cases where it did. Replacing the ECU entirely with a PowerFC however does seem to fix it always. Improving grounds fixes the problem...some of the time. I just replaced my engine wiring harness, and guess what...no hesitation, at least not yet. It seems fairly clear that the problem is electrical, and temperature-related, and has something to do with the way the ECU handles certain things differnet from the way a PowerFC handles them. I heard a theory once about the transition from open to closed-loop mode. Is it possible to run the PowerFC so that it transitions between the two in the same way as a stock car? If so, it would be interesting to see a PowerFC so programmed plugged into a car that currently, with the stock ECU, exhibits the problem.

jds

Still wondering if it is a grounding issue. Seems that replacing the wiring harness (esp. ignition) fixes it in some cars. Pettit was the first to tell me to replace the ignition harness. I've been monitoring this closely and it seems to go away when it is very damp and rainy - this would seem to point to an electrical issue. Wish I had more time to diagnose. Power FC is on my Christmas list, though...

I can't believe this thread was revived, hasn't someone demonstrated this yet? The theory is as wrong as it was a year ago. Anyone with a fuel pressure gauge can verify that the fuel pump, fuel pump resistor, and fuel pressure have nothing to do with the problem (the hesitation happens and fuel pressure remains smooth).

Thank you. No, nobody with a fuel pressure gauge ever listed their findings to my knowledge. If this is true than the hesitation is strictly a grounding and/or ecu issue.

I don't have any hard facts to add so I'll try to keep this short.

1) new batteries have solved 3K for some people.
2) think of what temp does to batteries, and connect it to the trend that 3k happens less when the engine bay is colder.
3) another test for everyone to think about and for no-one to try - what happens to the pump voltage with a PFC - did they remap to activating the relay at a lower rmp?
4) I've never liked the secondary injector theory since the secondaris can come on much later than 3K (right?).

Regarding engine code w/out relay. How does the ECU detect the relay?

If it detects it on the sensor side, then you can leave it hooked up on the sensor side and short the swith (or run a resistor).

If it detect on the switch side, then you can leave the relay in place and run 12 to the sensor side to keep it closed all the time.

Put in a new Die Hard battery - no difference. Secondaries come on depending on load, boost, rpm, etc. Not just rpm.

Problem always happens under 1-2psi boost, esp. up a hill (load) and cold. Not as bad when the car is warm but still there.

My 3K hesitation is worse when the car is cold; tends to go away when the car is warmed up to operating temp.

That's what I thought when I originally read this thread, but I'm not sure on the exact behavior of the OEM fuel injection, so I haven't said anything on it. On most dual injector systems, however, the secondary injectors usually don't come into play until the throttle position reaches a certain point (usually close to wide open) and the rpms are somewhat high (and I'd think that would be higher than 3000 rpm...). Pure speculation on my part, however.

Some additional things that the theory would have to account for in order for it to be a universal fix:

1. There is no consistency between cars of the same year - some have it, some don't

2. The concensus seems to be that the problem is not there when the car is new, but develops over time

3. The problem is often there when a car is cold but goes away when warmed up

This is a promising theory, and it will be interesting to see what turns up after several people try bypassing the resistor; also when a few people publish pressure test results.

I will add the info in this thread to the section on my site:

http://www.scuderiaciriani.com/rx7/3k_hesitation.html

Cheers,

Steve

It's been a week since anyone has posted in this thread...anyone try the test/solution yet?

I just got my car up and running last Tuesday but having boost problems.

I never had an RX-7 before I bought mine and rebuilt it so wasn't sure what the 3k hesitation felt like until now. Under light throttle, at exactly 3k I feel something like a fuel cut. So unfortunately, I have the 3k hesitation problem.

I'm going to bypass the resistor and let you guys know how it goes. Won't get to it until next weekend. Anyone know exactly how to make it hesitate? Mine's intermittent so I'm not sure how I'm going to do a test but I'll try to reproduce the problem over a few days and if I can't get it to do it I'll assume that the fix works.

Well, if anyone else tries it please post so I'll feel more confident in doing this...hehe. Thanks!

Great thread! I just bought a 93 Touring model, 5 Speed, and found that it has the 3K hesitation, not all the time, but more noticable shortly after warming the car up.

I am still getting it at times once the car is completely warmed up, especially in a curve, otherwise all appears well.