Rattlehead

What are some factors that can cause the injectors not to fire?
*Intalled new fuel pump installed so that rules it out. Psi *stays close to 55-60 psi
*Cleaned grounds under UIM
*checked and swapped around relays and fuses
*Reset ess

when cold the car fires right up every time. You wouldnt even know it had issues.
Now, the answer might be obvious but it doesnt start when hot.(I've ordered my RCT) So i cranked it and and immediately took out the plugs and they were dry. No fuel. I figured even with low comp it would start just takes extra seconds of cranking. As long as spark and fuel are there
Does vacuum affect this?
Realistally Im just trying to squeeze out whats left on the engine.

Any ideas?


Anyone know anything about possible Cobb AP repair?

MincVinyl

Well not ruling out low compression, but it tends to be a clearly dying drawn out problem. You should have noticed long hot starts > then not starting when at temp > then eventually trouble even after 5+mins of cooling.

Has this issue been going on for a while, and is it getting worse?

Rattlehead

For sure im not ruling out compression
Im 95% its compression(when my tester arrives ill know for sure)
but since i didnt see any fuel on spark plugs(they were dry as can be) when i cranked it on a hot start, it got me thinking. What if its only getting air, spark and *compression. Why arent the injectors injecting fuel? I did try some starter fluid for hell of it and it wanted to start. Is there something that tells the injectors not to fire due to low compression?

Its got a 20+ min wait time after shut off. So that might say it all. Depending on the numbers for my FD's compression test
the rx8s engine may have to wait.

MincVinyl

low compression won't stop the injectors from firing. The computer doesn't have any way of measuring compression levels, would have be nice if it did though. Hot start issues 95% of the time do come down to compression sadly.

If there truly is no gas when hot, I'd look into seeing why the computer may not be telling them to fire. Like if the engine is cranking slowly when hot for whatever reason. In my ventures with low compression the one thing I noticed was slower crank rpm when hot and cranked faster after cooling. Lower rpm = less compression wont be helping the engine start as well.

When you get the car up to temp how does it drive? idle? Hard to believe the engine would appear to be normal all around other than just hot starting if it was bad injectors.

Rattlehead

Thats what im thinking, how could it possibly know. If anything it would just flood. So im just trying to explore this see if i can squeeze some more miles out of the engine

Cranking is actually really good. It does have the upgraded starter. It definitely cranks close to 250(ill know more with tester)
Car idles pretty damn good. You probably wouldnt be able to tell anything is wrong(aside from noise that goes away with clutch engaged)even when driving it.
It drives really well and feels really good(driving it keeps me from selling it). Its Smooth. No hesitations. Ive taken it up to redline and it comes back down to idle just fine at stop lights. Just when i go to fill up or stall it. I have to wait to start it again

MincVinyl

Sure sounds like low compression. If you plan on milking the engine definitely try to keep it lower in rpm. When I started getting hot start issues among other issues mine only lasted about another hard 3k miles while receiving every upgrade possible. It'll most likely get to the point when it wont hold idle, and then it becomes a pain to have to heel toe every stoplight with fear of stalling>>20 min wait mid intersection.

mazdaverx7

iTrader: (6)

If the injectors are not firing, I would also check to see if you have spark. If you have no injector pulse and no spark, I would look into the eccentric shaft position sensor. You can perform a resistance test on it but even that will not tell you if its bad. It can test within spec and still be bad. You'll need an oscilloscope to check the waveform pattern when cranking the engine over to know if its good or not. I would just replace it if you have no injector pulse or spark.

CaymanRotary

Also agree that it’s more than likely low compression. Sure, will sound ok cold but once it heats up and doesn’t start, usually means new engine time.

Loki

iTrader: (1)

I would guess that the spark plugs came out dry because they were at operating temp and fuel didn't condense out on them, like it does in a cold engine. Also, being warm, it's not running cold enrichment.

Rattlehead

Cayman- it probably is, its not surprising. Car seems good all around hot or cold, just when trying to start it. Which im just seeing if maybe its something i missed.

verx- it skipped my mind that if theres no spark ecu might say dont bother with the fuel. Ill check it out.

On a side note, anyone have experience with VersaTuner? Unless somehow my cobb AP gets fixed im thinking of using that in the future with new engine

Loki

iTrader: (1)

What about the Cobb needs fixing?

I don't believe our ignition systems have spark confirmation, so the ECU has no way of knowing if there was spark or not. Your ESS should be fine since the car runs fine the rest of the time. It doesn't sound like you have a fuel problem, just good ole low compression

Rattlehead

Loki- i hook it up and it lights up and never does anything past the initial screen. Just kinda turns on and thats it

Loki

iTrader: (1)

Is that when connected to the car or a laptop? Or either? What does the AccessPort software say when you connect it to the laptop?

MincVinyl

I steered away from versatune and went the mazdaedit route about 2 years ago. At the time people were reporting issues with versatune causing random skips in power to various things. I'm sure it has probably been fixed by now, but I never saw anyone claiming it to be fixed when I looked into it.

Mazda edit UI is rather dated and setting the LS coil dwells was a chore since it wasn't in milliseconds, but as far as I can tell everything works.

dannobre

iTrader: (3)

It is possible that you have a wiring issue that becomes evident when the car is warm... but usually if that is the case and if it is in the ESS circuit the car will stop running when it is warm.

Did you say you have a large LTFT?

How long does it have to sit before it starts? Have you checked that the Pri Injectors are firing when it cranks when it is warm?

The only theory I could surmise is if the pri inj quit firing when hot and the sec trim way up it could still run and then it wouldn't start when hot till they fire again. Its a pretty far fetched theory...


Likely compression 😔

Rattlehead

Loki- i have not tried it with laptop. Its been a while since i used it, ill find it and check. The cobb is so much more practical than other softwares and would be a waste to throw it out

Minc- yea ive been reading posts about the 2 and edit is the favored one but like you said the UI. And the only reason i consider versa first is their UI looks a bit better. Ill look into seeing if problems are resolved

Dan- hmm well i did think it could be something hears up and stops it from working. But also yea not as likely
i had to look up what LTFT is and did not understand it. Or have ever looked at it.
i think i said the wait time for the car cooling down was larger. Sorry
i want to check if they fire, but man getting a noid lightin there means takin everthing off. Id rather do that if i have to after a compression test.
Haha compression is definitely more likely than constructing some theory as to why it wont start

When i had my Fc i probed an led into the ecu connector to see if injectors were firing. Is this a possibility at all? I understand if that really only aplicable to "older technologies"