Hi

had my rx7 rebuilt with a new crate engine from Mazda along with street port
car has had full new wiring harness, fuse boxes, fuel pump, injectors, single turbo conversion along with modified engine loom, coil harness is also new, fuel pump has been hard wired and fuel lines checked, stand alone ecu (link g4x) has tried multiple sets of plugs and coils such ign1a and oem
all the grounds have been checked out and pass, alternator has also been changed.
issue is whenever turbo spools up the car starts misfiring only if the the trailing coils are connected with leading plugs connected it runs to redline fine
the builder has said he’s checked the timing of the engine and it’s all ok

any ideas Would be appreciated as running out of ideas

 

Have you checked the coils for proper resistance and the coil input voltage when the misfire occurs? A coil with very low resistance or a partial short could reduce coil input voltage to the point that the plugs will not spark with higher pressure in the combustion chamber.

 

Where did the harness come from

 

I have been fouling plugs (15 sets) after a new engine install with a new IGN1 coil setup. These issues have lasted for the last 6 months. I looked at the coils, plugs, electrical systems, OMP overoiling, fuel issues,etc. I finally found the problem two weeks ago when I saw my lead coils were melted. My issue is, most likely, the grounding or a ground loop (new coils coming this weekend to hopefully fix the problem). After much research and many of the experts in the Yahoo PFC tuning group weighing in, we all believe it's a ground loop. I have an aftermarket star grounding system, with the batt- and engine ground right next to each other, but the ECU/sensor ground went back to the ECU through the engine harness, setting up the ground loop. The IGN1 ignition coil can misfire with just 0.7V of ground loop differential current. This easily could occur with my grounding system since my latest generation alternator, also connected to the star ground, puts out an almost constant 14.8-15.0V and the ECU is seeing 13.8-14.2V. I am moving the ECU/ground to the batt- ground location. This setup is actually used by Chris Ludwig and some others who make aftermarket wire harness kits. Hopefully, this will resolve my problem.

I would seriously look at your grounds. My solution might not be yours, but I bet the grounds are the culprit in your case too.

Mike

 

if you're on a haltech, updating the firmware with the coils connected will melt them also for whatever reason

 

If your FD is a Version 4 or newer be aware that the position of the stock coils was changed. If you use an old FSM (prior to 1996) you may be hooking up the coil harness, or plug leads, in the wrong order.

Your symptoms sound like what happens when you do that.

(I post this up quite often because if is a serious error that happens quite often, and the consequences can quickly lead to a blown motor.)

 

I’ve just spoken to the builder
he has cleaned all the grounds and moved the front space frame grounds to the shell just incase but to no avail

in regards to coils, it’s currently on the stock coils as he didn’t want to burn more ign1a

would an incorrect ground make the trailing coils fire at random ? He says the car isn’t drivable as soon as any boost is fed in, no boost there is no issue

it’s being a nightmare 4 years finding this same issue

 

did you manage to fix it with your new coils and moving the grounds ?

did you try running the oem coils again to see if the problem persisted with them ?

 

I believe I will soon fix the problem, hopefully. I did a deep dive into my aftermarket ignition harness and found the signal wires (5V and sensor ground, A and B on the IGN1 coil) and the 12V batt, batt ground and engine ground wires were all intertwined and the batt grounds and engine grounds were all tied together in the harness. The possibility of induction problems and ground loop problems was very high. I decided to remake the harness. I used shielded cable for all signal wires with foil and drain wires. Separate sleeves for all signal wires. Separate batt grounds (4) directly to the battery. Separate engine grounds (4) to the rotor housings. Separate shielded sensor grounds (4) to the sensor ground in the main engine harness. This should hopefully stop any induction problems and ground loop problems. Here are some pictures. I will hopefully install it this weekend and will see what happens. I did have a lot of input on the potential problems with the harness from many members of the RX7 Yahoo Tuning Group, who are very knowledgeable, with some automotive engineers. Also, it was recommended to go back to the stock coil dwell settings even on the IGN1's, which I was told, would be fine up to 400hp without any breakup.
Mike

 

It is not a well explained, or seemingly well understood, that, in the stock set-up, the leading coils, and therefore leading plugs, fire at the same time all the time.

The positioning of the plugs and rotors allows for each pulse of fuel to receive three sparks every time.

The purpose of this is to burn any unspent fuel from the first pair of sparks.

As I mentioned above, if the wires to the plugs are crossed, or the leads to the coils are hooked up incorrectly, it can result in this so-called "waste spark" firing into the fuel pulse as it enters the compression stage.

The symptoms of this seem very much like the issue you are having.

How exactly this would relate to your problem, I am not sure;

But somehow your sparking order seems out of whack.

 

 

The IGN1 are smart coils and can get screwed up with any errant signal along the TTL or signal wires (A and B). The electrical engineer on the tuning forum believes even getting a little current in the sensor ground from either a ground loop or induction can mess up the firing. My spark on the leads was weak (testing with the spark plug out and fuel cut by pulling the fuel pump fuse) before melting the lead coils. That's why I remade my ignition harness. We will see if it works. Also, make sure you check you plug wires for too much resistance. I was melting my lead coils only since they are the ones that have the waste spark, which has them doing double duty as compared to the trailing coils, as Redbul was discussing.

If it's your trailing coil, it still could be a signal wire problem, either from the stock harness or aftermarket harness, or even the ECU, or the spark plug wire itself. As Redbul said, make sure that the wires are not crossed too. Both the spark plug wires and the separate coil wires on the IGN1's. The stock coils cannot be crossed since they use the stock harness except in the case of the difference between the later version of the connecting stock harness. I vaguely remember reading in the forum years ago that the stock connecting harness was changed in the later series RX7. Maybe that's your problem? Is your car European spec, USDM or JDM and what year is the car and what connecting harness is it using? Look into that.
Mike

 

I just read another thread on the forum concerning the coils. It was not the harness that changed but the coil position changed in later series cars. Look at this thread. Check you colored coils connectors to make sure they are hooked up right.
Mike

Boost? Issue - RX7Club.com - Mazda RX7 Forum

 

There was a change to the harness as well. Different part number.

Early coil harness had a elaborate self grounding system incorporated in the harness.

Mazda, themselves, say the actual coils did not change, just their position

(But I have seen pictures where the twin post coil is shaped differently.)

 

I have told my builder to check the coil harness I believe he is using one from a pre 99 car, but he said it wouldn’t make a difference

 

would you have the new coil harness part number ? Every where I look it just says 93-2002 harness is the same
my builder has said the same thing and it wouldn’t make a difference using a newer one

my car is a 1999 car JDM import

he is trying a vr38 coil set up next

 

The part number for the coil harness is a bit hidden in the 1999 part catalogue. It is listed as an adjunct to the 18-050 "wiring, engine". The part number is N3F1-18-051. I see them for sale on Yahoo Japan/Buyee. I suspect Nengun will also have. Just google that part number.

The newer coil harness will not work on earlier FD version (those before Version 4). I don't know if earlier would work on newer cars. But why take that chance.

If you look at the USDM wiring diagram you will see the early harness has some funky grounding wires built in.

 

Nengun has, and cheap. I buy from them from time to time. Their shipping is reasonable and service has been very good.

https://www.nengun.com/oem/mazda/n3f...XZM1JiosJ340NE

 

 

thank you very much, will place an order and hopefully it cures the issue
will post up if this fixes it

 

Replacing mine with a new one did help eliminate some stalling and backfiring. i am not sure how they degrade, or how spark plug leads degrade for that matter.

 

If you think there might be a problem with the trailing coils wired wrong or configured wrong in the ECU, a timing light is a good way to check. The factory timing mark is designed for the front trailing coil, and you can either eyeball or use a paint pen to add a second mark 180 degrees away for the rear trailing coil.

 

Just to update
sadly did not work, car still has pinging noise as soon as boost starts building
tried cleaning all the grounds and moving them behind the space frame
builder has said it has even managed to melt an oem trailing coil with the correct harness

 

Wondering if the battery being relocated in the boot could be the issue ?
It would definitely generate more electrical noise which is linked to the coils firing randomly ?

I have told the builder to put it back to the front of the car to rule it out along with adding an optocoupler to clean the signal from any noise

 

How far back along the ignition circuit have you gone? What is the status of the ignitors? And finally the ecu?

My tuner also recommended I replace the engine/starter harness as well the coil harness, as I was getting electrical break up over 6000 rpm on the dyno, and they thought an aged out harness could be the issue.

I have not done this yet, as the '99 spec is NLA. I think the earlier "Engine" harness (not the "Emissions" harness *) is substantially the same.

(* what most people seem to call the "Engine" harness is actually referred to as the "Emissions" harness in the USDM wiring manual. In the later JDM manuals both the harnesses are referred to as Engine harnesses i.e. "1" and "2".)