3000-3500 rpm hesitation M/T versus A/T cars
 

Hello all. I need some information and opinions. It looks like I have the dredded 3K-3500rpm hesitation due to fuel injector transition when the secondary fuel injectors come on-line.

I need to know if anyone with Automatic Transmission cars have this problem. If so, did cleaning or adding ground wires take care of the problem completely?

The reason I ask is this. When I converted my car over to a 5 speed, I noticed that the automatic wiring harness had a large wire for the Black/Yellow and the manual wiring harness has the standard small Black/Yellow wire. I used the Manual Harness and spliced into the Automatic harness inside the car. The Black/Yellow is the positive voltage to all four injectors that is routed back out to the EGI Relay. The other 4 injector wires enter into the ECU separately to control the timing and dwell of the fuel injectors (I assume by adjusting the grounding time and duration). The wire diameter is about doubled on the automatic harness versus the manual harness.

If my theory is right, cleaning the ground connection is enough to cure the hesitation because the power supply wire is much larger going to all the fuel injectors in an automatic versus a manual harness.

If this holds true, a cure for the hesitation in the manual tranny harness car would be to rewire each positive side primary fuel injector over directly to the EGI Main Relay (the source of their power). This way, there would be no serious draw which might cause the hesitation in the primaries at transition.

Let me know your thoughts on this.

Many people have stated that the grounding is causing the hesitation and I can believe that is part of it. But another part of the equation might be the power supply wire being a bit under-rated to power the injectors at the transition point.

Thanks
Tim McCreary

mine is a manual, but after I installed my Power Fc it went away. I feel the hesitation is a problem in the stock computer.

Approx. what AWG are these wires?

I imagine the injectors are 14ohms so they take less than an amp of current each. If the wire is smaller than, say, 16 gauge, then maybe... That's a looong shot, unless the wire itself is damaged or somehow making a poor connection.

For now I'd say save yourself the solder and attack those grounds first.

I have installed the ground wires and the hesitation remains. The Automatic appears to be 14-12 gauge wire and the Manual appears to be 18 gauge. My thoughts are that the primary injectors are probably near maximum when the secondaries start on. My thought is the power draw is robbing from the primaries.

I also understand that the aftermarket computer appears to always eliminate the problem. But if it is the computer, why did it not start immediately when the car was new? Most people start to see the hesitation after some time and I believe this is due to corrosion and poor connections with the grounds. Also after time, the heat of the engine probably affects the connections and wiring for the fuel injectors. Not sure if this has any factor in the problems also.

Tim

Bump, anyone??

I like you're theory Tim.

I've been thinking that the hesitation might have something to do with power supply to the injectors. Unfortunately I haven't had time to test any ideas yet.

Well, there is a lot of validity to what you've said. The wearing wiring and connections could very well be the cause. FWIW, I have a degree in EE, so I'm not just blowin' smoke ;).

But then again, the other parts change with age in the same way. Maybe the injectors' age are part of the equation (also?).

I haven't really measured what duty cycles of the injectors are at during transition... hell, I'm not exactly sure if the transition is discreet like people have told me. And I wont believe it until I see the data. Besides, dont other things change as well. I remember reading something about the air-pump, somewhere... but that may have been BS.

But otherwise, consider this. As injectors age, they tend to have more and more mechanical resistance to moving (opening). And in general, injectors (esp. the older ones) don't perform well at low duty cycles. How "low" depends on the physical construction of the injectors. If the ECU is "easing" the secondaries into activity during the (supposed) transition at a low duty cycle, the tired older injectors would be more likely to stay closed and flow less (or no) fuel, until the duty cycle goes up. This behaviour may be different among the stock and aftermarket ECU and may account for problem dissappearing when going to an aftermarket ECU.

But hey, this isn't the only plausible explaination. If you do the work yourself, the wiring will be cheaper than getting new injectors (which may not fix a thing).

I thought of this also, but have heard of people replacing their fuel injectors with new ones (upgrading) and having RC Engineering clean/rebuild theirs (not necessarily changing the electric coils in them) and still having the same problems. Never heard of the air pump. It shuts off at around 3750, a bit higher than the injector transition hesitation, so I doubt it is a factor.

Thanks for the comments, need more opinions.
Tim

This was brought up a while back and I think it was decided that it was to do with the fuel pump and not the grounding or the injectors. I can't remember the specifics but it had to do with the fuel pump switching voltages to go into high output mode. Fix was to wire it so that it was in high mode all the time. I never have had the hesitation, problem, so I didn't pay much attention.

The fuel pump theory has been disproven by many people. I have even tried it my self with no luck.

On my AVC-R, I can monitor injector duty. When accelerating though ~3000rpm, or whenever load is placed on the engine, the primaries seem to go up to around 60% then the secondaries come on and duty cycles go down to ~35-40%. It is right at this point where the hesitation occurs.

I suspect that it is a wiring issue as well, but no one has answered the question:

Do the automatics suffer from the 3k rpm hesitation?

Also, what would make mazda use heavier wire for the autos?

Good info, guys.

Tim, what year was that auto harness? It would be interesting to see whether the following year manual harness has the larger wire too.

ISUposs, do the secondaries come on with the primary cycle drop simultaneously? Or is it in sequence vs. RPM? Also are the secondaries pulsed, or do they just blow 100% after the transistion RPM?

yes, as far as I know

They still run at the same duty cycle as the primaries.


For anyone who might know, where do the injector wires run? for instance, you obviously have at least 2 wires running from the ecu (one +12V for the primaries, and one +12V for the secondaries). Does the other end of the loop return to the computer, or does it get grounded off somewhere? If it's grounded, where is it?

I think we're on to something guys!
All this thinking makes me want to go out and tear my wiring harness apart! :)


Also, InsaneGideon, according to scuderiaciriani.com, all years of US spec FDs show hesitation problems. They are less prevalent in the newer years,but regardless, they are there.

No I don't have the hesitation, but neither do many 5 speeds.

To answer some questions raised:
Mine is a 1993 RX7 that was an automatic, but converted to 5 speed (93 R1 Donor) using the 5 speed harness. I took the small connecting harnesses from X-05 and X-14 and modified them by carefully removing the pins from the manual and auto harness plug ends and swapped pin positions coming from the engine to match the corresponding pin position in the manual ECU. The manual harness has a smaller power lead to the fuel injectors versus the Automatic. If you look in a factory shop manual, you will notice the power to the fuel injectors passes from the battery, through the EGI fuse, through the EGI Main relay, through the X-05 connection inside the car, then out to the injectors. The power wire branches off to all four injectors inside the harness near where the injectors are. All four injectors then return the other wire back to the ECU via B1-01 harness plug. All return lines are Light Green (LG/R, LG/B, LG/W, LG).

Power to the injectors is Black/Yellow (B/Y). This is the power supply wire I am talking about. It is common to all four injectors.

With this said, grounding to the motor will do nothing to help the fuel injection directly as there is no direct grounding loop outside the ECU. Grounding back to the ECU should definitely make a difference and has in my car. But it did not eliminate the fuel injector transition point. Technically the fuel injectors appear to ground inside the ECU, thus normal "Grounding" as many people understand is not an issue. Grounding the body and engine better may help the actual body grounding point from the ECU to battery and this may be why it helps. I am not certain, but I can only make the assumption based on the wiring schematic that the computer controls the injection cycles by altering the timing and duration of the grounding. This is why I took a ground directly from the battery into the ECU ground bolt.

weaklink: As far as the fuel pump relay, I have already bypassed the 1K resistor with a direct wire across the plug, so my fuel pump is running full power all the time. It did not make a difference. It may make a difference in people who have not changed their fuel filters. By increasing the pressure, they are probably avoiding fuel starvation that is occurring due to a blocked filter.

I have a 1993 and 1995 wiring diagram and both are the same as far as the wiring plug and wire size is concerned. If you look at the X-05 harness plug in the back of your manual, you will notice a 10 pin blue plug in the manual harness with all 10 wires basically the same size. The Auto harness X-05 uses a 21 pin blue plug with 5 of the pins being about twice the diameter wire as the other 16 pins. The plugs are much larger to correspond with the larger wire also. Now some of these also branch to the Auto Tranny, so that is why there is more and why I believe they used a heavier wire. It is one of these heavy wires that supplies power to the injectors (Black/Yellow) in the automatics.

Now the big question in my mind is: Did Mazda correct this problem with the later year cars? Anybody in Japan having the same problems? I am curious if they changed the wiring harness to separate injector power lines more or dedicate them differently. I have heard they went from 8 bit to 16 bit processors for the ECU, but not sure if there was a change in the harness also. There is three different PowerFC computers for the RX7's in Japan based on years.

Need Help People!!
ANY BODY ELSE HAVE SOME OPINIONS AND THOUGHTS??
I cannot believe this problem does not have a root cause. With this said, we need to find it and bury it once and for all.

Tim

The problem is solved when swithcing from a stock ECU to a Power FC. If it were the ground itself at the injector it would still be a problem no matter what ECU your using. The Systems weak link may in fact be the ECU. The stock 8 bit ECU is likely to be the culprit here. The Power FC is a 16 bit ECU and is better at making transitions like that and the "Hiccupp" is gone when swithcing to the Faster ECU. I see that as the problem. Some people have fixed the transition on Stock ECU'd cars by adding grounds but it may not have a 100% effect.

DP

hesitation
 

i have the same problem i.e. hestation at 3K. I have grounded everwhere i can think of however i have not added exttra grounding to the ECU. Only the Engine bay and the Cat. (Exhaust)

I have also replaced the Oxy Sensor (Unversal single wire).

The problem seems to be better occacsionally however the hesitation returns and is right pain in the arse!!

I have just purchased an RY Amamia computer hopefully, this will erradicate the problem once and for all!

if this does not work i am at a wits end as wat i can do??

ZoomZoom, I dont think we can pin this directly on the ECU yet. These cars didn't do this from the factory, and many still don't. Also, the PFC is, after all, programmable. One could just adjust out something like this by adding more fuel to compensate for flakey injectors/wiring... to a point anyway. That's kind of a shotgun approach.

Then again, maybe the transistors in the ECU that ground-control the injectors are poorly soldered or otherwise failing.

I just thought of another possibility. Does anyone have any fuel pressure readings during a hesitation? The "shock" of drawing fuel through another set of injectors may cause a brief pressure oscillation in the lines. Maybe a weak pressure damnpner is a culprit.

Tim, if additional devices are sharing the supply line like you said, I'd say that's the reason as well. But hey, try tapping a large gauge fused wire from the injector power line (close to the injectors) directly to the battery. That should give you your answer :)

If you want to be thorough, borrow a portable scope and make sure EACH injector is being activated by the ECU. It could be just one that's dead. Though I'd suspect some fueling problems at WOT as well, if this was the case.

This is all very interesting to me. I used to own a 93 R1 5 sp and never experienced any issues with hesitation. I believe that this issue must be due to the aging of some parts in the car. As mentioned before, this does not happen from the factory, only after time.
The fact that a aftermarket ECU cures the issue tells that the factory ECU is either recieving bad data that it can not process (electrically) or that the ECU itself has some issues with connections on the board. Great discussion
:D

WOW, can you say archive post. this is a great thread. im currently about to start an auto to 5speed swap. is there a possibility this will happen to me? does it have anything to do with the swap, or just 5speeds in general?
also if another ecu fixes the prob. for others, wouldnt this seem to be at lest part of the fix? but insanegideon is right about adjusting the ammount of fuel. does anyone w/ a pfc that had this problem still use stock fuel ammounts? oh and with a pfc, does it come w/ a new wiring harness, mabie the wires still have something to do with it?
ok im just confusing myself, mabie this will give you other guys some ideas.

ZoomZoom,

If the root cause is just the ECU, then it would occur from new. I believe the ECU is a contributing factor and a major one at that, but not the root cause. I do believe that either the power to the injectors or the type of computer has much to do with how the injectors react and eliminate the hesitation. My thoughts are why are there some cars running without hesitation and what are the differences between those and mine?

SNracing, are you changing motors to a 5 speed motor or going with just the tranny and retaining the auto motor? Email me direct at mccreary@cove.net for some information on the conversion. Also remember, there has got to be one root cause creating this problem that has eluded discovery. My premise is the power wire is too small after it has aged and grounding has deteriorated. Fixing the ground does not always correct it, so it has to be something else.

I have been told that PFC does not cure the problem, only the ECU change.

Keep it coming, anyone else have more information?
We need to find out once and for all.

Tim