Hello over the last two weeks or so I've noticed some intermitten missfiring - initally when started it would complettely cut power randomly once or twice then not come back during the drive. Now as of today when motor is hot I am getting heavy missfiring and a total power cut. I just recently replaced plugs with BUR9EQ/RE7C-L. Just looking for some advice on where to start as I am sure there are dozens of places to loose time and $ on parts.

 

Ordering NGK 8156 wire set as well as these have not been replaced in my 8k or so mile ownership - 82k on OD btw

 

not sure what is easiest to check, but resistance of the plug wires should be under 16K ohms, and new ones are around 8k
next stop would be the battery cable connections, they need to be perfect.
then its like fuel system, you could check fuel pressure, or just change filters

 

So the factory wires were a range of 13k-30k replacements were as stated around 8. Car is still exsibiting the same issues, on cold it can redline and pull through all gears with power. After 25m or so after firing the motor is when the power issues come up. Isn't necessarily when just secondary injectors come online either can be a constant low-medium power missfire. Always ran heavy premix- could my filter be causing these sorts of issues? @j9fd3s know of any writeups on how to remove/replace FF on S5s?

 

its harder to do a write up than to change the filter, really. the only tip is that you want to disconnect the battery first, the positive cable is close enough to the filter where it can be an issue.

 

So I tested post filter pre dampener for pressure and got about 35-38psi. also held pressure drop test losing basically nothing after 10 minutes. swapped filter anyway as I had it. Still no luck, let it warm up while i cleaned up within 10 minutes and I was in the car it started misfiring under load. CEL holding at idle which is new, with throttle goes away/misfires and comes back. No saved codes to point me anywhere. Manual says injectors next, is there a way to test them without tearing down and removing?

Motor has been strong till this point some I don’t think I need to worry compression side as it’s a dual rotor what feels to be fuel cut misfire.

 

since you have an S5 according to your profile, 2 things come to mind:

Faulty OMP
or
Incorrectly set or faulty TPS/idle screw causing an idle surge/sputtering/throttle fuel cut

pull codes, if there is none you will have to check them during a failing drive cycle. these ECUs purge codes every key off unlike newer cars, you gotta remember they're 35 years old.


it could be something more in depth like a failing injector wire or failing injector, however neither of those would trigger a CEL because these cars have the equivalent IQ of about 10.

 

Yes, 91 Vert.
I honestly do not suspect injectors either, as the way the fuel cuts, it wouldn't have been a progressive failure. It isn't isolated to primary or secondary either.

Had a funny course of events after my comment yesterday. Saw the guide mentions how to test voltage on a hot O2 sensor. At warm idle, I had 2.2V; while on accel it maybe only went up 200 mV, and decel stayed at 2.2V. Book calls for 0.5V–1V on accel and 0.4V–0V on decel. I unplugged the O2 sensor for testing, and oddly enough it started running better—drove it around for a few minutes in better shape than the last month. I then plugged it back in and had an hour of drive time last night ripping around keep in mine no CEL since replugging 02 and keycycle. Super odd... Ordered a new O2—will have to cut and extend it for the RB header, however. Prayful it'll fix my issue?

Funny you mention OMP though, as I did have to remove it to do the water pump. Gasket was leaking after reinstall. Replaced gasket and RTV’d the housing just before this issue arose, I guess. Not sure if that points any fingers. Any recommendations to cross OMP off my list?

 

i wouldn't be too faithful that an O2 would cure the issue, it is a rather useless input on these cars. it's possible you have a wiring issue, moving the harness might have cured the problem temporarily. if the OMP is setting a limp mode, there will be a code for it and the CEL will come on when the problem occurs.

OMP failures are one of the biggest problems with the S5 vehicles.

 

@notanymore I will put OMP at the top of my list, any recommendations to check other than pulling code?

Today I drove the vehicle 20 minutes ac on etc pulling great zero problems. run into a store and on key cycle it’s issue is back. fiddled with the wire again with no luck. parked for an hour and came back to it strong again full power + ac without issues.

Seems to be a more active issue on key cycle of hot motor. Maybe worth noting that AC when random misfires are present typically makes the car undriveable here’s a quick video to show it’s power on this drive after the hour intermission.

https://imgur.com/a/xHEvptW

It’s my understanding that when OMP codes are present the vehicle goes into limp and is a noticeable condition, please correct me if i’m mistaken here. I haven’t experienced this, going to drive again shortly hopefully get codes to come up to video its condition. Didn’t have my jumper earlier to check, will make sure I ride with one.

Also this vehicle and all my rotories have been premixed. .5-1 with known good omp. .7/1-1 with questionable.

 

doesn't appear to be a limp mode issue from that video, limp mode would prevent you from even getting near redline and you'd be limited to about half your tach. this seems like an ignition issue, plugs and/or spark plug wires.

 

First I want to thank you and others for responding to this thread. Hopefully can bail someone out when I find the solution (very soon I pray).

Plugs: NGK RE7C-L (x2) and NGK 5777 BUR9EQ. The old plugs were stock, switched to RX8 leading.
Wires: NGK (8156) RC-ZE02 — all measure between 6–8k ohms, while factory originals were probably 13–30k.
Fuel filter: OEM replacement.

The vehicle is completely stock outside of a Racing Beat full exhaust with a bad gasket hence the Civic-like exhaust note (it’s on my list..)

I took another few videos earlier that ill provide in a links here. I am driving the car close to WOT, just to show capability and actual affects of the missfire.

Video 1: https://imgur.com/a/b5shI9V
This was after a cold start and a 15-minute drive. I ran into a store, and the video starts when I’m leaving the parking lot. At 15 seconds in, you’ll see a new kind of misfire, rather than the pure stalling hesitation I’ve been experiencing. Then, at 30 seconds in, you’ll see the typical behavior what looks like a complete fuel cut. When this happens, it slams me forward under load with zero power output. Oddly enough, the code and issue actually cleared itself by the last straightaway in the video so I did not get to pull a code.

Video 2: https://imgur.com/a/khUhxOI
This was taken directly after video 1 when CEL and misfire state cleared. Car all of a sudden was back to normal, typically after hot start and misfires the car would sputter until it cooled back down.

Video 3: https://imgur.com/a/J5RS7pO
Taken 20 mins or so later with AC car is happy to rev - typically after I would experience CEL on hot motor I would literally have to sputter back to my destination, mainly stating that I am not getting absolute replicable issues.

New O2 sensor should be in and installed within the next few days. Not getting my hopes up, but at least I’ll have a working one that reads correctly. I’m still working on pulling codes the next time it acts up. To do so can I check codes with the engine running, or do I need to turn the key back a click?

 

are the plug wires new or just ones you tested for resistance? unfortunately resistance test won't rule out a faulty boot letting spark leak out.

 

Plug wires are a new set yes. I think its safe to rule them out as it's an issue across both rotors. Maybe I should test my coils though ?

 

couldn't hurt, it really seems like the ignition is breaking up somehow. granted i couldn't watch the videos, imgur seems to have an upload speed of dialup on their servers, a 2 minute clip taking 5 minutes to watch with 10 second intervals of buffering ruining all continuity.

 

Got a CEL on a drive tonight that stayed- flashed a few times no misfiring however. pulled the code and only stored was a code 9 for 91 I understand this as a water thermosensor code. I’ll look at the manual and see what this side draws up.

 

In your video, the temp gauge is at half. S4's are always at 1/4.
Is half up normal for S5's, just curious?

 

S5 normally half way, S4 is normally 1/3 of the way. the S5 is a dummy sensor, it stays at half for a wide range of temps until it is way too hot, then it begins to climb past half. if the gauge ever gets past half, pull over immediately with an S5.

 

The S5 Gauge is weird, it has like 3 zones to it.
from 0 to just below the middle, it reads like an S4 gauge, its accurate, but has some damping
from just below the middle to the middle, its basically so damped it doesn't move,
and then over that all the damping comes off, and its needs to because this is like 100c.

so yeah if you see the thing move, engine is about to be well done

 

You'll have to find out why you're running hot. Your thermosensor is not related to the overheating issue however, if you're ECU fixes your fuel trim at 80C and you're climbing to 100 it could be an issue.

Check your fluids and make sure your oil and coolant are where they need to be. Check for leaks. If that's all good then check the thermostat out. If that checks out then we have to start suspecting engine coolant seals. Do the champagne test to see if you're getting bubbles when you're warmed up. If you have a big enough funnel it won't overflow.

An oil pressure test wouldn't hurt either.

I say always do the easiest things first. Don't get worried about the seals just follow a process of deduction. Easiest to hardest or cheapest to most expensive lol.
You might find out you're just low on coolant or something benign like a faulty temp gauge. Easiest to hardest.

One thing for sure, you have to find out why your gauge is in danger zone.

 

I didn't know that the s5 runs at half.