Stuck at a certain rpm
 

Hi miata lovers,
Two days now my car have a big problem i can t find a answer to!

Without any kind of warning my 91' 1.6 miata started to get stuck at a certain rpm and can t go up further. It happen between 2'000 and 3'000rpm (seems not exactly the same rpm each time) and almost constantly althrough there is some few times the car function perfectly fine for a few minutes. At this precise rpm the car can t take one rpm more (reminds me a limiter or a motorcycle antiwheel slippage) and start shaking a bit (like a bycilinder or a car with cylinders out of work type of rumble). When i put the car in neutral it revs perfectly without any hesitations.

i checked for a clogged cat (i have a normal air flow at the end of the exhaust to) and for plugs wires that seems to work well (i have 5'000miles "new" plugs, fuel filter and injectors and cat). My maf seems clean.

my afr is very good all long as well as my o2 sensor values (even when the problem happen).

Could you please tell me if it could be transmission related (i get a lot of clutch slippage) because in neutral i dont have any prob or if my problem happens only when i'm in load for other reasons?

i would like to thanks you for your help, i'm a bit isolated in europe when it comes to miata and if i can enjoy this pleasure it s largely because of you!

Is your car on the stock computer or do you have an aftermarket ECU?

Just because it seems like you have normal exhaust flow at idle, doesn't mean the converter isn't clogged. Pull out the pre cat O2 and try seeing if that changes anything. Reducing the restriction should slightly improve the concern if it is the cat. The converter could be partially clogged where when you put a load on the engine, it is forcing broken cat material against the exit side of the converter.

it will also help to let everyone know what type of ECU you are running.

Hi, sorry for the late i wasn t at home.
i have stock ecu with a tdr card (idle valve is recirculated via a check valve to prevent leaks). For the last 4'000miles i checked my afr that was perfectly regular and very nice (11.5-12@wot, 14.6 @idle+ cruise).
i found out that the seal of the idle valvle on the intake manifold wasn t good (my mistske it was during the change of the injectors) i also find out that the silicone hose of the integrated wastegate was damaged.
Now the rpm blockage seems to have disapear (i had strangely had it one or two time). The engine is back to a good afr when running...the only change is that when i release the gaz at low load and low rpm, the afr go from 14-15 to 11 and then lean (before it was directly from 14-15 to lean)... the other big problem is that my afr at idle is at 14.7 (like before) for a few second and then it slowly decrease to 10-11 (so, harley style, low and iregulate idle).

does somebody can help me?

Yes. Don't try to run a turbo car on the stock ECU.

ok thx for the advice. I dont have choice for many reasons. I already made 5000km with this config (only mountain pass) and i m sure i ll do a lot more when i ll found the solution that is, i m sure, not related with my stock ecu + tdr config. Are the idle valves prone to fail?

Stock ECUs are designed for NA setups. Just cause you drove X miles on the setup is irrelevant. We cant help you if you just give us your AFRs. We need more information .Did you even try the test I suggested to check for a clogged converter?

no, i'll love to do this test, but it s for me not possible to do a single mile with that noise and without a cat (strict laws there that explain stock ecu too).
based on what i read and the way the car was running, i still think i can have a reliable setup with stock ecu (how FM could sell these if it was not fontional). I perfectly understand that stand alones are THE way to go and i know that i much limited than you all, i m ok with it.

The fact that only the idle is affected make me think to idle valve trouble...what do you think... i change the seal between it and the manifoild but does a bad idle valve could cause it?

:facepalm:

Listen to me, an idle valve will not cause a car to not drive over a certain RPM under load. Under load means the car is moving and the engine is performing work. Just cause you rev the engine in neutral is basically free spinning the engine. It isn't trying to move the vehicle thus no load.

You need to perform the test I suggested to check for a clogged converter. You dont even have to drive it far, just down the road and back. If you have a clogged converter, and the O2 sensor before the converter is removed, your car should be able to accelerate more due to less back pressure. If you don't want to do that buy a back pressure gauge and install where the O2 sensor is. That will show you how much pressure is building. When the exhaust cant get all gasses out of the system it builds and builds causing the engine to run poor. An engine is basically a giant air pump. It pulls air in then expels it. If it can't expel the air then it's efficiency is limited thus the limit in RPM range.

You're using the stock ECU with a piggy back adapter. The RPM limit should not change. Do you have any data logging capability with the TDR thing? I'm not familiar with that unit so if you can post the link so I can see what it is I could help you out more.

don't waste your time on this guy. just move on to people who actually listen

I think my explaination of the problem were bad too...
he will explain it better than me : "As soon as I get on the gas, the car behaves almost normally, but is reading very rich. Under cruise/normal load I read 10.5-11.5, and when engine braking it still stays around 12, doesnt lean out as it normally would. The last oddity is when I go under heavier load, the AFR goes to about where it should, around 13. Idle is also reading 10-11 when normally it is 14-14.5"... that s exactly what s happen with me!

What happens if you disconnect the TDR card? Does your idle stabilize at 14.7 or is it still rich? I would suspect the piggyback is somehow interfering with the normal idle.

On your words i did it and it s exactly the same (note that nor the tdr nor the red injectors did this problem at install)... the problem started at the EXACT time i started to have this kind of low rpm limitation (this limit seems at the exact instant the turbo would normally start spinning)... it disapeared when i changed the idle valve seals but today it started again (rpm limitation) to complement my riche idle...

Are you reading the AFR from your own wideband or the stock lambda sensor? If not, you might want to check the value that the stock lambda sensor is giving during idle.

i read it from my afr and my o2 sensor. Values are perfectly correlated if it could help (DAMN RICH).

realise i can resume my question like that... is this something that is prone to faillure (i couldn t be intrinsequely due to my setup wich proved to be ok for long) and could cause both my two symptoms that are : permanent rough/rich idle AND temporare rpm blockings (it s related for sure i felt them comming at the same second).
I check ALL my tubings that are all perfectly fit (checked the turbo screw wich is as new).
i also wondering if a failling hose between the turbo and the integrated wategate could induce dommage or deregulate something that provoke my symptoms (for me only a compression leak on side and a full close exhaust side wastegate clapet)? Or at the opposite is something related-to or induced-by my symptoms could lead a wastegate hose to implose.

why do all your posts read like spam emails?

sorry about that
spammers are foreigners...you got your answer?:winner:

English is his second language. Or perhaps third.

I wish I could help. I've got nothing.

I'm assuming the TDR box failed and it's no longer adding fuel and it's going majorly lean.

or this botched injector install that involved the idle valve for some reason is a culprit:

:confused: :confused: :confused:

still trying to figure out what an idle valve was removed from the TB to install injectors.


Pictures of this idle valve, and the rest of the engine bay please.

Does this car have aftermarket FPR?



Dear Europeans:

The universal law of cause and effect states that for every effect there is a definite cause, likewise for every cause, there is a definite effect.

what injectors did you install? and why?

For the tdr card i m not lean but rich (iddle only)... but i already remove it and it changed nothing to my iddle problems...

I have smalls red rx7 injectors (was iddling perfectly for 5'000miles and many others use it with vodoo box or tdr without problems).

I dont have a fpr (new fuel filter only) but again (tell me if i m wrong) if my problems where linked to the lack of a fpr i'll have suffer from it for long ago...

hopefully i'm not european! But i ll tell them!

So I changed my plug wires, wires, checked for vacuum leaks, checked maf, checked turbo on both side, checked cat (removed totally).

Please tell me if my last suspects are worst to change:
- egr valve (could lead to rough idle but with lean condition in my understandment)
- ignition coils
- ect sensor (what about this??)
-idle valve stick closed(a bad one could cause rich idle, but could it explain the blockage in rpm?l

I'll love to have your other idea too...i m totally lost.

maybe check your rear tires. or your headlights.

already done...love your irony...so funny

your ECU + TDR combo is not equipped to handle the 460xx injectors. you're basically flooding the motor to where it can not longer combust under load or stay stoich at idle.

THAT'S NOT THE PROBLEM BRO.
LOTS OF CARS WITH A DIFFERENT PIGGYBACK ARE RUNNING FINE!!

lol

PM vlad for tuning.

:bowrofl:

ok i dont have 490cc but 290 secondary rx7 reds...they use it for tdr compressor with stock ecu, they also specified that they are perfect for stock ecu in many other place. They also iddled at 14.7 for two month...

I told you that s not a choice (i have 10years of programming behind me so this part wasnt the most difficult for me). I spent ALL my free time to learn from 0: reading, thinking, doing stuff that are at the opposite of my curriculum. I do it because i love this car more than everything and i would sleep one hour a night to get it work again. I not a mecanic, it s passional, i dont have 1% of your knowledge but i think i deserve to be not publiquly humiliated each time i talk. This knowledge i m sure could solve my problem if you use it this way.
thanks

To add my new tests:

- when i disconnect the idlle valve (iscv) connector, the iddle still start at 14.7 and then go down rich (no changes)

-if i create a vacuum leak post throttle body the idl get back to 14.7 and is then perfection (maybe it could help for diagnogstic)

Is your idle valve stuck or does it move freely?

does your TDR device thing have a vacuum line going to it? is the vacuum line on the FPR still connected/good?

your AFR mixture is obviously off. Both tests above increase the amount of air in the mixture. However, both should also significantly raise the idle speed.

for iac valve i just inspected it nothing more...for iscv i just removed the connector to see if i get a difference (that wasn t the case!). I have the 14.7 and then drop rich in cold and hot condition (maybe that put out of cause the iac). Do you think i can get a sure way to test if it open freely?

thx for your help!

yes it have on and its connected perfectly...:noes:

so if i go further both my tests weren t explaining anything?

disconnect the vacuum line on your FPR -- check if there's fuel in it.

I tried it when checking for vacuum leaks...the is no fuel at all in there...
thx again!

Bot?

Ok i checked my cylinder with an endoscope...cylinder 1 have a lot of fresh black deposits (overly rich conditions...). I m pretty sure my uncountrollable iddle and blockage at low rews problems was coming from there condition was comming from that... it seems that the wire connector of the cylinder 1 was slipping in his rubber anchage and not gerting the bottom of the coil.

now the engine dont even start, it crancks for a few time until it make a clonk and stop cranking (cylinder 1 is now full of fuel). When i wait for the fuel in cylinder 1 to evaporate it will crank again untill full again...i know the cylinders are pairing so it could not really be coil or other "upper" ignition problem (and the plugs are passing the spark test on cylinder one). Plugs and wires are also oem brand new...

what could make cylinder one not to fonction if there is fuel + spark?. It could be i think a stupidly fast feeding injectors (too rich to even ignite) but i swapped them without a change. I suppose a lost of compression could be involved i dont know if a certain amount of compression is needed for the ignition or if the fuel will still ignite enough to not permite a total flooding of the combustion chamber? What other could cause this fuel not to ignite (timing?but is this possible to see other cylinders to perfectly combust?).

at this point for me the car have hydrolocked because of the fuel going up and cant be ignite because of the bad cylinder one contact on the plug wire (at the coil). I think it just stopped the engine but i didnt bend anything (the piston will not move freely and without suspect noises isnt it??)
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Perform a cylinder leak down test and compression test across all cylinders and post your results. You may have a burned valve or other mechanical issue.

are you ready to listen to us about doing things properly? or are you going to destroy another engine before you do?

Never destroyed one before...i tried to figure out problems nothing more...for me i cant see any of your remarks that could have avoid/warn me about an eventual hydrolock and/or or put me in the way of this totally non burn fuel (and it seems there pretty obvious that my piggyback is out of cause because two cylinder would be impacted)...

sounds like injector leaking

thx for the comment.
that was i was thinking but i swapped it without change (i even fitted back the stock injectors for the test). I think the misconnected plug wire could have this effect too but why now that ive reconnected it i could not burn this fuel anymore ? Bend rods ?or valve (as supposed by one of you)?

ok i ll try to diy an equipment for...thx

Hi,
i payed a famous car swapper (did the third of the eurodrift series cars an was turboing ae86 25 years ago) to check the car and he couldn t find anything with a quick check, without disasembling the engine. He told me to change the maf that was for him the fault. I bought a new one and it changed nothing.
I tryied to remove the wastegate and get the "system" without.... Any change there too.

I also tried the compression of each cylinder and i have enough of it (8-9bar on each cylinder).

i just need to know what i could check now. How can i now try some other diagnognostics? What are the other possible fails i should looking for, thinking to my symptoms (car smoking (fuel odor) and stalling few seconds after starting (if starting)). Do you think it could be the the advance had a sleeping and is not correct anymore? Do you think the head valves could be sticked or bended??

injectors, plugs, plug wire, fuel filter, maf are new (changed for troubleshooting this problem). Spark is ok...

i m now for month without a car and i m urged by all persons i know to buy a new car. I would not and will spend my next years walking and thinking about how to figure out this problem... true love for my little (sick) baby.

thank you for your help (for my number 1 supporter, yes my tires are inflated. Dont need any reminding)

Last thing the mecanic that came said, as every person that saw it to help me (approx 10) that the engine was "turning" freely and without any suspect sound when turned by the starter...

injector leak or (direct) fault is to exclude (tryied 2 set of injectors + all seals brand new). I ll try to check with a multimeter the voltage comming there..