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I’ve been in circles trying to fix my break up issue. Under load it will break up at 5k rpm, but revving in neutral is pretty much normal all the way up the rev range (4 psi in neutral). You wouldn’t know you’d break up at 5k with load…
The car has run great, if there’s a misfire I always just take it as a sign to replace plugs. And it always solves it, but to my surprise this time (5 weeks ago) even with exactly the same symptoms, it didn’t.
For weeks I’ve been replacing parts one by one to slowly narrow it down but still haven’t solved it yet. I only get to work on it when I have free time. Car runs normal: smooth idle as before, runs great to 4500 rpm normal boost operation then after it just breaks up and I let off the throttle immediately. No smoke. Zero starting issues. This makes it tougher for me to solve since I’m expecting it to be an ignition issue.
I’ve been through most, if not all posts regarding this topic and unfortunately some don’t have any conclusions so I decided to ask for your guys’ help. (s7, stock twins, knightsports ecu 14psi, upgraded fuel pump, midpipe, exhaust)
Things I’ve done:
1. New Plugs 9’s
2. New Leads NGK (found t2 wire faulty)
3. Replaced Fuel Filter (was quite dirty) & air filter
4. Swapped good tested set of spare coils (old ones tested fine also)
5. Checked alternator (13.8-14.1)
6. Swapped out another ecu and still the same
7. Aftermarket FPR works fine (set pressure unchanged)
8. MAP sensor checked and cleaned
9. All boost and vacuum lines checked thoroughly no leaks
10. 4 year old battery might need replacement but always fully charged while testing
11. Solenoid rack checks out (s7/s8 no rats nest)
12. Triple checked all grounding and cleaned most points.
All this is somewhat surprising considering the car ran perfectly for years with this setup untouched. Apart from the necessary plug changes and maintenance procedures, I’d consider this car maintained well and virtually unabused and she’s never given me any major headaches; this being the biggest one so far in more than 10 years of ownership.
I will be pulling out the injectors soon to have them tested and cleaned, as well as taking the alternator to a pro to have it checked. Hoping some of you who’ve had this issue and solved it can help point me in the right direction.
Are you are certain its not boost creeping above 14psi?
Knightsports told me I was tuned right to the edge of stock injectors at 14psi on stock twins on my 4 Beat.
When had to put in a midpipe because I melted down my highflow cat racing I had boost creep at 5,000rpm and the injectors went static, hesitation and huge backfire with flames from all the exhaust flanges (immense pressure).
I put in an exhaust restriction flange to keep boost at 14psi.
That worked till the flange bowed out racing and became less of a restriction- the next boost creep incident brrke an apex seal because I was street driving on stock plugs instead of 11 heat range and just 1 bottle of octane boost instead of 2 (4Beat is tuned for JDM 100 octane).
do you have a boost gauge? how much boost are you running?
As Blue TII said, you are probably running too much boost for what the fuel injectors and ecu can handle. That is a quick way to blow the motor.
I also have a restrictor in there to keep boost right at 14psi, put it on when I went full 3” exhaust.
I do have a boost gauge and when the primaries kick in it’s perfectly behaving as it should, comes on nice and early at full 14 psi just before transition, then I boost up to 14 psi again with the second but misfiring.
I had my mate tail me to watch for smoke or what but he doesn’t see anything abnormal apart from the obvious misfire. No smoke on idle either.
It’s usually a plug change scenario but this time it didn’t fix it. I ordered my plugs from Amazon, could it be bad plugs?
The car has the same setup for years and yes I do have access to 100 octane. It really feels like an ignition issue when the secondary ignition comes in but so far I have already replaced what could be the usual suspects.
Most posts I have seen often have leads issue, coil issue, fuel filter. But one pointed out it could be the alternator, however I already tested it with the car running and it checks out good. No spiking voltage.
Battery is old and has been recharged a few times since Covid lockdown era but testing now it’s at the right voltage also…
When I replaced the fuel filter I found it to be quite dirty and was confident at the time that I found the culprit, but upon road testing it was still breaking up at the same revs. All that dirt maybe made it to the injectors?
Double checked for kinked hoses and never found any, solenoid rack under the UIM makes it easy to see and go through.
Also, I’ve been through a limp mode 3 years ago so I know how it feels like. Even the primaries won’t light up in limp mode, not even free revving it. Free revving now passes the usual 4 psi in neural test.
Went through the ignition harness and I forgot to mention that the blue plug clip has gone missing, but it appears to be locked it right without it. Can this be the problem?
Also failed to mention I had a coolant plug (bottom rear of the engine underneath the intake elbow to the firewall) burst and sprayed water around the area, and no I didn’t overheat. Maybe the water wetting the coils and harness started it?
I can’t say exactly if the plugs were already fouling / having the misfire issue when this happened. Could be breaking up even before this point.
Are you running an aftermarket FPR? I recall seeing a talk a long time ago where the length of the vacuum hose (if it's too long) can cause crazy fuel issues at a set rpm.
Do you have a wideband O2 sensor? Fuel pressure sensor? I wouldn't push a rotary engine hard without either of those, they don't have a reputation for surviving tuning problems or fuel system problems.
I have tuned a bunch of these rx7's on the powerfc and the problems you are describing most of the time are linked to these areas. Throttle position sensor not aligned correct. The fuel ramp takes too long from primary to secondary fuel ramping up. Boost exceeds MAP sensor capability.
I have also cleaned up a lot of cars tunes with powerFC's that had problems like this by adjusting all of the settings correctly and then tuning the fuel base map.
I have also seen a lot of tunes on these people's cars and most tunes could be better. Steve Kahn does well.
That's a good point, 14psi is very near the limit of what the factory RX7 MAP sensor can measure. It might be hard to know how the KnightSports ECU will react when the MAP sensor is at the max reading.
This happened out of nowhere, and it’s almost exactly the same symptoms as when you’d foul plugs. So when this happened I thought it was just another signal having to change plugs that were more than a year old anyway. I don’t drive the car often, maybe 400 miles a year at most.
I have verified with Knightsports all the info when I got the car years ago about what the car has been tuned for and whatever they have since was never touched or upgraded. (Thanks, google translate)
I’m leaning towards a simple ignition issue. Car ran great with my setup for years no problems. The car right now would build boost in primary 14psi til 4500 (nice clean pull), dip, then boost again making 14psi again around 5000 but starts to break up. I had the same problem back then around 7 years ago and the fuel filter changed on top of the new plugs fixed it.
Right now I’m thinking the water burst incident started the issue. I’m pretty sure the coils, harness, leads got a bit wet. So I changed all those a few days ago with a new fuel filter and still no fix.
Could a weak but often trickle charged battery cause any of this?
Blue T2 plug on the coil doesn’t have a lock clip, but secured nice and tight, can that lead to a break up also? Leads are in the correct positions too.
How do ignition harnesses get tested? I only tested for continuity the other day and it checked out fine. Pretty sure the they got soaked.
Swapped in an stock s8 ecu yesterday and still broke up. I know a twin power would help out at this point but I’d rather get it sorted out first as it might be some electrical fluke and this setup has worked for great me for years.
I’ll be looking into the TPS today, as well as changing the battery. I’ll try to take some videos of what I can find. Thanks again for the inputs!
Just a thought… I remember changing the plugs first. When this didn’t work I replaced the plug wires a day or two after.
Testing wires I found T2 to be way off spec. It’s the same blue connector that doesn’t have a lock.
Could I have fouled the plug in there when I road tested with the broken lead? And so even after swapping out coils and new wires I’m still using the same new set of plugs might have already fouled the T2 one?
Sounds like that very likely is correct. Non-firing could lead to fouling which might not want to clear up even if the proper spark voltage is now present.
*The above 2 posts were also me, the laptop was logged into that older account of mine sorry for the confusion…
I found 2 ground wires that were not connected properly, cleaned and secured them. Also replaced some suspecting vacuum hoses around the solenoids. Didn’t fix it.
I did one pull just to check if I fixed it, and I confirmed that I do get up to 14 psi after transition to secondary turbo then past 5k break up time. As soon as I hear the break up I let off and that’s probably 5200-5400rpm
So revving in neutral, take it to redline wot it will not break a sweat - means only primary injectors are working here, secondaries not used yet right?
But WITH LOAD it will break up CONSISTENTLY at 5k rpm mark after transition.
What’s at the 5000rpm area?
- Secondary injectors should start to come online here? But aren’t they online when the primary turbo makes full boost early on below 2800-4500rpm (load from primary turbo)?
- What happens with the ignition at 5k mark that will point to coils or spark?
Sounds like that very likely is correct. Non-firing could lead to fouling which might not want to clear up even if the proper spark voltage is now present.
Thanks Dave for replying…
It just crossed my mind and I didn’t know if it made any sense… thinking I’m going around in bigger circles when all I need again is a new set of plugs. However I only went for 1 pull and stopped and changed the wires soon after.
Do broken wires ruin plugs that easily?
Would a broken clip / missing lock on the blue T2 harness affect coil and harness performance even when nice and tight?
It's been a common experience that once plugs are fouled in a rotary engine it's often difficult to clear the fouling. This often happens if they are fouled by brief running after cold starts. Fresh plugs are then sometimes needed to get the engine started.
So I would say that a faulty ignition wire could do the same.
I don't know specifically about the effect of the broken clip, but if that resulted in a discontinuity in the plug wire, then yes it could.
When ive experienced breakup, i usually try to lower the boost to see if that helps. If thats a possibility, maybe you can try that to see if it helps w/the breakup. If it does, then you can continue troubleshooting from there.
I just wanted to give a quick update on this issue in case someone is working on their car with the same symptoms... never really got the chance to work on the car since my last post.
So I received and installed my new plugs along with a new ignition harness today (ordered from a local NGK distributor). I started with the T2 (suspected fouled from the bad wire) and it surprisingly looked fine. The T1, however, as shown in the photo below looked new. That got me wondering, something's definitely off. I inspected the plugs and compared them to the new ones and it felt like there was a strong possibility I installed fake plugs.
I went to compare these 'fake' ones with the old plugs I had taken off previously and what I found are described with photos below...
These fake plugs were bought off Amazon.
T1 FAKE: didn't even fire up much LEFT: FAKE you'll see there are little chips around encircled area when the original one on the right is clearly smooth. Prints pointed by the arrow shows thicker text, the Q's clearly show this LEFT: FAKE the blue lines on the base of the plug are very bold FAKE: the printed code has the letters misaligned completely. If someone wants a better quality version of the photos just let me know and I can email high res ones.
Since T1 didn’t fire I tested the new NGK plug wire I had on and saw 1k ohms resistance and thought it might be too low. So I decided to use my old T1 wire since it was at 4k ohms.
Went out for a road test and I did 4 second gear pulls: first had misfire and sputtering but the breakup was gone. Second and third pulls were getting clearer and by the time I got to my fourth pull it was decent and clean.
I’m blaming the misfire issue on a low tank of OLD gas so I’m quite certain it’ll clear out once I put in new fuel.
This was an odd fix. I’m guessing the coolant didn’t damage the coils, but it showed me that the T2 wire was probably arcing. I’ve swapped coils, plugs, plug wires and tested them with the multimeter many times, knowing it’s ignition related never really looking closely into these particular plugs because for more than 10 years of replacing them this is the first time I’ve seen this. I usually get my plugs from a supplier but back in January I decided to try and get it from Amazon for a change since it was quicker.
So this is how it all went:
It looks as though the coolant issue brought out the problem with the old T2 wire, but I didn’t think much of it then so I just changed the plugs. Still breaking up (not knowing they were fakes), I then swapped in new plug wires after checking resistance (T2 way off) and changed the fuel filter and was still breaking up. New genuine plugs, new plug wires (apart from T1) along with a new ignition harness fixed it for me.
So apparently the new misfire is still around and I can’t get rid of it.
The latest fix was the alternator, which was proven to be bad due to it getting wet from the coolant hose burst issue. Fixed that and installed it today and the misfire is still there.
It happens still at 5k-6k but this time it clears up after that. It’s way lighter than the ignition break up I had prior to replace to original plugs and new wires.
Could it be secondary injectors being a bit clogged? Perhaps not spraying out enough when it starts to turn on?
Secondaries will come on at different RPM depending on load, but at full throttle they should be coming on closer to 3000 RPM. So I don't think the transition is the culprit here.
Big thing is that ECU is a black box, you don't know what it's doing. It's possible you are going dangerously lean and getting detonation - 5000ish RPMs are where you will hit peak torque which is typically where detonation will happen.
May want to get a wideband so you can see what is going on. That will give you a LOT of clues if it's going too rich or too lean. If you don't want to install a wideband permanently you could also look to see if there's a dyno around you with a wideband where you can do some pulls with the wideband and see what is happening in a controlled environment.
Secondaries will come on at different RPM depending on load, but at full throttle they should be coming on closer to 3000 RPM. So I don't think the transition is the culprit here.
Big thing is that ECU is a black box, you don't know what it's doing. It's possible you are going dangerously lean and getting detonation - 5000ish RPMs are where you will hit peak torque which is typically where detonation will happen.
May want to get a wideband so you can see what is going on. That will give you a LOT of clues if it's going too rich or too lean. If you don't want to install a wideband permanently you could also look to see if there's a dyno around you with a wideband where you can do some pulls with the wideband and see what is happening in a controlled environment.
Dale
Thanks for your thoughts, Dale. I’ve been focusing on the ignition (plugs, wires, coils, harness) for a while and since I tried the refurbished alternator today (14.5v idle from 14.1v) with no cure I am now going to look into the fuel system. Leaning out at 5k was what I thought the alternator might be doing not giving me enough volt at that rpm…
I always imagined the secondaries to be coming online with the first turbo also and not rpm based (is this correct?), I do get full boost with the first and no misfires. Only when I reach around 5k does it start to misfire then disappears at around 6k.
I installed a new fuel filter a week or so ago, found it was quite dirty. Before all this the car was stored for quite a while that’s why I was thinking I might have blocked secondaries too? I will also replace the tomei fpr but it tests fine with regards to pulling the vacuum hose off and back.
I managed to borrow an igniter, which is the last thing I have to try out in the ignition system. When I go for a test I let off immediately upon any sign of break up so it’s probably the last ignition related test I’ll do.
03-10-23, 06:42 AM
