I have gone in circles trying to track this issue down for 2 seasons now with no luck. one day when daily driving the rx8 i went to do a little pull and noticed the engine sounded like it was hesitating/struggling past 4k rpm. There is no cel, no recorded misfires, and no symptoms/unusual noises under 4k rpm.

Parts replaced due to suspicion: fuel pump, ssv assembly, fuel injectors, lower intake manifold gasket, vacuum solenoids, maf, coil packs, and plugs.
Modifications include: AEM cold air intake, racing beat midpipe, magnaflow catback, coilovers, vfad and air pump delete.

The issue started out only under load past 4k, progressed into audible hesitation/cutting even when free revving (still only past 4k rpm). My research is leading me in the direction of either an omp issue, electrical issue, or vacuum leak. I would have posted in the troubleshooting forum but did not have permission. I have already looked at every thread related to this issue, but no suggestions listed there has resolved or helped the issue.

One night decided to try pushing the engine past the ssv actuation zone to try to better diagnose, got to redline in 3rd resulting in the vacuum line connecting the OMP injectors to the intake in front of the throttle body to be popped off, spewed oil everywhere. The audible rattling cleared up at about 6k rpm but still power loss.

Descriptive symptoms: physical hesitation+audible rattling past 4k rpm, STFT spikes when throttle open, 0 audible/physical issues everywhere under 4k rpm.

Thank you in advance for any input

 

Interesting. What's weird is oil in the OMP vacuum line and that it popped off. Under throttle nothing there should be pressurized. If the injectors don't hold vacuum, that might be possible, but did the oil come up from the omp end or the intake nipple end? I'd say it's more common to get oil in the intake from blowby.

While probably not the cause, I'd clean your ESS, it's a good idea anyway and maybe you'll see a change.

Vacuum leaks tend to show up at idle, what are your LTFTs? And what do the STFT spikes look like? Full throttle or partial throttle? STFT will flop around, this is normal, but if you're finding it in the +/- 15 or more range, that could be a clue.

 

I hate to add another part to your list, but I have similar issues anytime it rains out. I believe it has to do with either the MAF or throttlebody or the wiring, granted I havent been able to fix it yet since it is so intermittent. Usually the fuel pump and vac valve system is higher rpm issues.

I dont see how that vac line would pop off or throw oil everywhere. I am pretty sure the oil injectors should be closed if no vacuum is applied.

 

A few notes to be added: engine was rebuilt by Rx7 specialties about 35k km ago, when I bought the car I was premixing too heavy up until the issues started, when the air pump was deleted the vacuum line to the solenoid was not plugged off originally, and when I replaced the fuel pump I noticed a grey film coating the pump assembly and the interior of the tank, like some sort of residue that could be wiped off by hand.

I believe the STFT would spike to about +15 - +20 revving in neutral but will get a more accurate reading this week once I get the upper intake manifold back on.

Where the 3 vacuum lines connect to the intake between the throttle and MAF is where the vacuum line popped off and spewed oil everywhere in the engine bay. when I traced the line it ended at the vacuum rail for the oil metering injectors. I've also recently noticed a hairline crack on that said line.

I am planning to get my hands on a vacuum test kit but yet top do so to confirm proper vacuum. I briefly suspected something wrong with the vacuum chamber itself but have not found any info about anybody elses vacuum chambers going bad. Another brief hypothesis is the one way check valve under the upper intake manifold.

 

Not sure if my recent quick reply sent, sending now as quote.

Few supporting notes to add: I was premixing too heavy when I first bought the car but have since been premixing sparingly, when I replaced the fuel pump I noticed a grey film coating the pump housing and gas tank interior, the issue started a few weeks after deleting the air pump.

The STFT spiked around +15 - +20 revving freely from what I remember, I will get a more accurate reading this week. At one point the car did throw a lean code as well but haven't been able to replicate it since. The Hose that popped off is one of the three located between the throttle body and MAF. After tracing the line it led to the back of the oil metering vacuum rail connected to the nozzles.

I have previously tested an ESS from another running rx8 but did not notice a difference but ill try to give the wire another check. A hypothesis crossing my mind are the one way check valve connecting the vacuum chamber to the upper intake manifold as I've heard that could cause similar issues. Another is the vacuum chamber itself failing after something going wrong following the removal of the air pump but I haven't crossed a vacuum chamber failure from what I've seen. I also came across a hairline crack in the line that was blown off in the incident but no oil residue surrounding. I currently have the upper intake manifold removed for re inspection of the vacuum system but do not currently have my hands on a vacuum test kit. is there anything else I should check for while I have the manifold off? I can send images of parts mentioned if helpful as well.

 

I’ve sent a reply to this thread twice now last week but no updates have been shown, what have I done wrong?

 

Apologies for the late response, I have now figured out how to reply properly hopefully.

Important notes to add:
-The ESS has been replaced and cleaned
-There has not been oil in the vacuum line since the incident so I'm guessing it only pressurizes once the SSV should be opening
-The line that popped off is the part number N3H1-20-341C, there is a small crack on the end that connects to the nipple on the intake before the MAF
-After further inspection I've noticed the engine does seem to idle somewhat rough but the rpm is steady, although almost sounds like a partial "brap"
-The issue started happening around 1-2 months after deleting the air pump
-Originally premixed close to track ratios when daily driving by accident prior to the issues, later premixed much lighter

The upper intake manifold is currently removed to re inspect the connections and OMP lines, is there anything else I should check before reinstalling the UIM? I will get a live reading of the LTFTs and STFTs once reinstalled but I do remember the STFT peaking around +/- 15+. My personal suspicion at the moment is a vacuum leak, But I do not have a pressure test kit nor a smoke kit. I can provide pictures/vids of parts/descriptions if helpful, any input helps.

Thank you

 

Wait a second.

"Before the MAF"? There are no nipples before the MAF on the stock intake or the AEM. Picture of your setup please?

 

Appologies, I meant one of the 3 vacuum nipples located between the throttle body and MAF, specifically the one that routes under the upper intake manifold to the OMP vacuum rail

 

 

Yeah thats not the stock intake, can you take more pictures of the engine bay? You also have strange looking ignition coils

Check the wiring for the MAF and see if it is frayed or broken anywhere.

 

The brand of coil is "np boosted" I learned afterwards that they are not the greatest but have also tested with other known working OEM coil packs and no difference.

The intake setup is the AEM cold air intake, with the included meshes installed. The VFAD connector off of the MAF wiring is disconnected since my VFAD is removed, but no visible frays or splits though.

Is there a test I should be doing though the OBD scanner to determine if the MAF is reading correct? I have cleaned the MAF and swapped with another as well with no difference either time but understand that if a wire connecting to it is getting incorrect voltage any sensor would read incorrect.

 

If the VFAD is removed, is the vacuum line to it capped? That would cause unmetered air if not. The nipple is under the throttle body, out of sight, you have to feel for it.
The main thing for MAF or vacuum leak related issues are the fuel trims. Once the car is warmed up and idling, short term and long-term fuel should be near 0, under 10 at worst, and your MAF should read 5.7g/sec for 800rpm idle. If that's not what you see in OBD, share what it shows and we troubleshoot more.

 

Update: assembled the UIM today, confirmed the VFAD was capped off, and tested the readings at idle.

STFT (Bank 1): -1.6 - +3.3
LTFT (Bank 1): 0
Air Flow Rate: 5.4 - 5.8 (g/s)
Ignition timing advance cyl 1: -5 - -2.5*
Rpm: 780-850
o2 sensor current (b1-s1): 0.03-0.07 (mA)
Lambda (b1-s1): 1.00 - 1.026
control module voltage: 14.15 - 14.35 (V)

have a few other readings such as throttle position a,b, etc. but not sure if they’re important. Have a couple revs again and still will rev in neutral but can still hear an audible change past 4k rpm, and subtle pops when letting off the gas. Have videos but are too large to post, SSV also knocks at idle after a year of being replaced with the s2 SSV. Is there anything else I should check for/inspect?

is it possible for OMP nozzles to get stuck open and let pressure from the combustion chamber into the intake between the MAF and throttle body? I feel like that could explain the vacuum line popping off from the intake under full throttle to redline, but unsure.

Also is it possible that there was a tune on the car that I was unaware of before owning it? I did disconnect the battery when I deleted the air pump, and the issues started happening within a couple months afterwards. Afterwards I did the pcm reset procedure with the steering wheel, and the ignition reset with the brake pedal.

 

That all looks ok. Here's something to check, if you have a buddy, look for arcing at the ignition wires, either at the coil or spark plug end. Easiest in darkness while someone else cranks the car. I'm experiencing something similar, faint shimmy/hesitation after 4k and turns out, one coil is arcing to its housing.

OMP nozzles aren't in the high pressure part of the cycle.

Totally possible to have a tune and not know it, but none of the memorry reset procedures you can do will change it. You would need something like FORscan or Mazda's shop computer to read the firmware details.

Are your motor mounts ok? For your line popping off, I wonder if it was mechanically pulled off by engine movement.