Cranks but won't start after rebuild
 

I have read every page on starting problems and can't figure this out.

I have a 2007 RX8 and just rebuilt the (6-port) motor. It cranks, but does not start.
The combustion chamber does not seem to be getting fuel - I know this because after cranking repeatedly and pulling out the spark plugs, the plugs are not wet with fuel.

Has spark (checked each wire with spark plug tester).

Before the rebuild the motor did sputter to life once, so I know all the systems work.
We rebuilt it and put everything back together. Checked wiring diagrams for the injector plugs. All the fuses are good. The security system warning light is not on. I've reset the ECU using the brake pedal pumping method x20. Compression seems to be good (though I've not actually tested it) because we get a good sneeze out the plug hole if the plug is not in when cranking.

So on the no fuel to combustion chamber thing:
- Fuel pump works (pulled off fuel hose, gas gets pumped out)
- Checked power at one of the injector wire connectors, and one of the wires has 12v when the car is on

Any ideas?

... Is it actually getting fuel to the engine, despite the pump being on? What I'm asking is there a possibility there is a blockage in the line.

My guess is a lack of compression. Try injecting atf or 2 stroke oil into the service ports while cranking and see if it starts or sounds like it wants to, if does, then it is likely a compression issue.


As for the dry plugs, when you say a sneeze, I assume you mean fuel spray? If so then the injectors are working.

There's definitely fuel getting to the injector manifold. I took off the fuel line, and watched it pump out.

As for lack of compression, it's a brand new rebuild. I guess something could be wrong there, but the lack of fuel seems to be the issue. When I say sneeze it's just air, not fuel, and the plugs consistently remain dry when trying.

I have squirted oil into the combustion chamber, but that did not help.

Today I was able to get a code reader on the thing and it crossed a bunch of possible problems off my list. like the throttle position sensor is working fine (if it had been at 100% it might have been triggering the anti-flood thing). Also, the RPMs were displayed, so it shows the crank position sensor is working.

I'm stumped.

Well if the injectors are not firing then you need to start there with your troubleshooting. Bad rebuilds are actually very common.

Engine----> Sympton Troubleshooting -------> Engine cranks normally but doesn't start

M A Z D A

Great list. Have done a lot of that. But there's some I can't do with the tools I have, "Inspect fuel injector control signal wave profile at the following PCM terminals." And some I'm testing a little more backyard mechanic like watching the fuel pump instead of testing the pressure.

The thing that's so curious is that the car did have life before, so the individual components should still work. I keep thinking that there's something not plugged in, but I took the upper intake off (yet again) and checked everything and it all looks good.

Is there a way to test to see if the injectors are trying to work?

You can plug in a Noid light tester to the injector plugs That will tell you if the injectors are getting a signal. You usually can hear them open as well with a mechanics stethoscope placed on the injector body

Check the power to the power side of the injector. you should have B+ voltage on each one. I think the wire is white/blu if I remember correctly. You could just have a blown fuse

Great suggestion. I'll see if I can find one.
Stethoscope is great idea too.

The wire connectors are so hard to get to and get off, but I was able to get to one and did test and it does have positive going to it. So fuse is good. (I have actually checked every fuse with a multimeter).

Am I missing something about getting the connectors off, or is it really always that hard?

Will this one work on Mazda? Doesn't specifically list it...

Noid Light and IAC Tester Set 11 Pc

The injector connectors are a bitch. Whenever I remove a harness I clean it real good and use d grease on the injector connectors. But I also label both side of each injector connector to avoid mistakes. A plastic engraver would be smart too if you ever plan on doing it again.

good idea. I'll do that when I take them apart again.

I carefully, twice, looked at wiring diagrams and so am sure they're in the right place. But even if not, it seems they'd be squirting something in somewhere, so plugs wouldn't be dry. So am still thinking something more basic is wrong with the fuel delivery system.

You know what they say when you assume.

Cranked engine while feeling one of the injectors (the only one I could cram my hand in to reach!), and I felt no clicking at all from the injector, which I assume I'd feel if they were firing. Is that right?

If so, it means something's preventing them from firing, so would be a big step in troubleshooting.

Are all the condensers on the wiring harness secured to the block?

Well, I don't know about condensers specifically. Where are they? Everything that came off the block is back where it started. (connectors in the right place, ground wires to block, crank position sensor, knock sensor, etc.) I don't see condensers anywhere, where are they?

Update. Still not starting. Have gone through all the troubleshooting as much as possible and can't find a cause. Here's what we know:

- Car cranks fine. OBD2 data shows about 200+RPM cranking
- Crank position sensor and toothed-gear in place and working fine
- Throttle position sensors working fine according to OBD2 data
- No check engine codes
- Injectors DO seem to be putting fuel in, at least some times, as we have found the plugs with fuel on them and fuel vapor is coming out the exhaust.
- Injector wiring is correct to the wiring diagram
- Security system not activated
- Spark plugs are getting spark (used visual spark plug tester)
- spark plugs are connected to the right coils
- Coils are connected to the right connectors
- Compression is good (tested with compression tester) (also have injected oil into the combustion chamber to increase compression with no effect)

So we have air, fuel, compression, and spark-at-the-right-time. Why won't it start? Any ideas?

If you are getting fuel vapor out of the exhaust it is likely flooded. Have you tried to pull start it?

Flooded makes for almost no compression ...so the odds of it starting is really low at 200rpm

I don't think it's flooded, we have done deflooding procedures, left plugs out overnight, started with foot on the floor, etc.

But am open to trying anything. What do you mean pull start?

Put the front tow hook in....hook up a tow line to another vehicle and pull it up to about 20 mph. With the ignition on ...let the clutch out slowly in second or third gear and it should start if it's just flooded fairly quickly. Expect a huge smokeshow and difficulty idling for a while....but it should run after a few minutes if all else is OK

If it won't pull start you have other issues that flooding .....but try it as it's the easiest way to get it started if it's a nasty flood

Unfortunately can't pull start it because it's an automatic :(

I'll look at other deflood threads, but I'm not convinced it's flooded...

That sucks. ....The flooding issue is very difficult sometimes. You could try some starter fluid carefully into the intake as well...that is much more likely to ignite than gasoline.

when you crank it without L plugs do you get 3 nice clear compression pulses for each rotor? Try putting your finger over the plug hole and you should feel 3 nice poof's per rotation.

If you have fuel...and spark....the only thing left is either the timing of when they occur...which the ECU controls without any user adjustment...or you just don't have enough compression when it tries to fire.

still no start :( Spent a while playing with this today. Did several de-flooding procedures. Fuel pump fuse out, crank with foot on floor on and off a lot. Took plugs out, let crap fly out until not much was coming out (and it didn't smell like gas anymore). Tried starter fluid, but I think I'd have to take the upper intake off for it to get into the combustion chamber, otherwise it's just pooling on its way there.

But even after all the deflooding, it still doesn't start. (though every once in a while it does).

Yes, getting three nice compression strokes out of each rotor. It was the back rotor that was more flooded (more stuff came out of it when we took the plugs out and cranked -- I wonder if it is because the front is on jack stands?)

Any other thoughts or ways to test?

So, getting spark and fuel and it's not catching? Do you get the sense that you're getting any kind of combustion? Even one ignition event?

Yes, it was a typo above, what I meant to say was every once in a while it sounds like it's starting. Not much, not really a splutter, but just enough to give me hope.

Still no start: Today we tested each spark plug to actually see the spark, and also tested compression.

Each spark plug has a spark. The front-TRAILING spark plug had the weakest spark, though. All others were some shade of bright blue; the front-trailing was yellow and not bright (still a spark, though). I've read the trailings aren't important, so can't imagine that would prevent the car from starting, but am now thinking about replacing coils, wires and plugs (since this seems to need to be done regularly anyway). BUT --- the car started before with these same coils, wires and plugs.

Compression. Getting three "strokes" of compression in each rotor. The rear does seem to be stronger than the front, which is worrisome, but the front definitely has three pulses (I'm using a standard compression gauge and just watching it move and trying to guess.) Putting some oil in the front rotor did seem to improve the compression. But there's still some compression (and they became equivalent when I put the oil in, so I've a hard time thinking that this is preventing it from starting.

Another note is that the trailing plugs both had a lot of gas in them from flooding, as I think it's harder to clear those in the regular deflooding ways, so we removed them both and dried them.

Another note, the trailing sparks start about 4 seconds after the cranking starts, but the leading start pretty much right away. So this is helpful to determine the wiring is right.

Still no start.

Air, fuel, compression and spark, but no start. What's the deal?

I checked out this page, RX-8 Help, and now I'm thinking it's generalized low compression.

I compression tested again (again using a regular (not-rotary) compression tester) and get 58PSI on the rear rotor about 56PSI on the front rotor at 220 RPM. This is FAR below the required compression to start, so would completely explain the motor not starting. (we are at 5300 feet above sea level which does make a difference according to Foxed.ca - Rotary Compression Calculator, but I don't think enough to let it start :( )

Remember, this is a completely new rebuild, and the compression is equivalent on both. So is this expected? Could we have done something wrong that would lower the compression (but not eliminate it) equivalently across both rotors and all three "chambers"?

Thanks for your help.

Not nearly enough information to start diagnosing where you went wrong in the rebuild process. What kind of apex seals and springs did you use? Did you reuse your housings? Rotors? How do you know they were within spec? Did you figure out the cause of low compression to begin with? Otherwise how do you know you resolved the issue?

When we got the car it would not start. We injected oil in the combustion chamber and actually did get the engine to run for a few seconds, so that showed us that everything was OK (except something internal).

Upon taking it apart, the main problem was that the front bearing had worn out, and an apex seal had broken. There are/were some scratches on the housing, but we showed them to two different experienced RX8 Mechanics and both said they were ok. (very shallow). the eccentric shaft was deeply scored, though, so we replaced it and several components in the front stack.

We rebuilt with seals and springs and everything else from Atkins and replaced everything. It's our first rebuild of a rotary engine, but I've done pistons before. So we were really careful and meticulous and checked tolerances on the apex seals, etc.

Yes, re-used housings and rotors.

We just tried putting 10 more CC of oil into each combustion chamber, apparently not enough vacuum to suck it up from a cup, so I injected in. It definitely sounded more like it wanted to start, but still didn't. Funny thing is that when we first put the engine back together and tried putting oil in it, the vacuum did work well enough to suck it in. So something has changed.

Atkins seals are known for having inherently low compression. If the entire rotating assembly was worn that badly I would have expected the housings to wear in a similar pattern. Do you have any pictures of the engine while you were rebuilding it?

Well, we did not check the spec on the internal dimension of the housing. But when putting the engine back together it seemed quite tight in there.

The rotors and housing weren't work, it was only the eccentric shaft and the front stack (because of the bearing that spun)

here's a pic of the rebuild

https://cimg2.ibsrv.net/gimg/www.rx8...c08e15a4da.jpg


Yes, rebuilt it in the living room :)

Here, for example, is a picture of the spun bearing.


https://cimg3.ibsrv.net/gimg/www.rx8...d785eac297.jpg


Also, here's a pic of some of the wear on the rotor, which was not much at all.
https://cimg5.ibsrv.net/gimg/www.rx8...7c2bf191ba.jpg

New coils, plugs and wires? If not, when was the last time those were changed?

They wouldn't cause ridiculously low compression numbers like that. Though I'd definitely want to get a second opinion with a rotary specific tester rather than trying to eyeball a mechanical gauge like that.

Did you make sure to properly gap the side seals? If they were binding then that could definitely cause some major problems.

Did I read that right? Your using a regular compression tool to check the compression? It's my understanding you can't get real numbers this way. Try to borrow a rotary compression tool

Yes, using a regular compression gauge.
I realize this isn't he best way to test compression, but not sure where I'd get a rotary compression gauge.
And there's lots of examples of it working:

My pressure doesn't get above 60PSI

There seem to be two ways of doing it. I did it by taking the valve out of the tube of the compression tester, which allows you to see the needle bounce up and down for each face. and after the first rotation it's consistent and you can read it pretty well. The other way is to get the reading of the "whole rotor" by leaving the valve in, but this doesn't tell you if each face is compressing properly.

The only strange thing is that the compression is low across both rotors. I'm still hoping for something that will fix it that will not mean I have to pull the engine out and tear it down again (or get a new engine).

A piston compression tester will show you if the engine is toast, it just doesn't tell you the whole story. But 60psi is fucked either way.

Yeah, I'm inclined to agree.

What could go wrong to have low compression across both rotors?

Faulty batch of seals, upside down springs, improperly cuts seals, or out spec rotors, housings, or irons.

Despite what the internet says about rotaries having less parts than a piston engine, etc. Rebuilding a rotary is not simple.

At this point there's no use speculating, pull the engine.

I just recently rebuilt my motor and it wouldnt start either. I had multiple issues but the main two were compression(atkins cryo seals and solid corner seals) and my fuel pump was bad( only primed 30psi). I replaced my fuel pump and put atf into the service ports of my intake(the 2 nipples on the lower intake manifold) while bumping the motor over with the starter. It needed alot of atf and once it was going it ran rough until i was able to driver around 50-75 miles. expect lots of smoke and many chances for it to stall. Mine now starts cold every time on its own and warm most of the time(still breaking it in and i need new spark plugs from fouling out my old ones). I currently have 150 miles on my motor and its worth every penny.

Your freshly rebuilt engine still hard starts when hot and it's worth every penny? :lol: I don't think you know how things are supposed to work.

me2151, what do you mean by "a lot" of ATF? More than 15cc?

I figure I should try one last effort to get it started like that before pulling it. How much oil is too much?

When it's enough to liquid lock the engine and do even more damage.

�� ok. So manual says 10-15cc. So twice that? 4x that ?
also thinking of doing it with 2-stroke oil instead of ATF. Does it matter?

and doesn't there need to be enough room in there for some gas and air? ;)

Got it started today! found a mechanic who works on RX8s and he suggested WD-40, so we sprayed it in through the spark plug holes on each side, and bumped it around. quite a bit in each lobe. and it started.

I'm not sure if it unstuck something or if it just provided some liquid to help create the compression, but either way it did the trick.

BUT … it only ran for a minute and then died. But while it was on, it ran really smoothly. More troubleshooting tomorrow on why it stalled out -- likely there's still something really wrong, but it was a nice moment :)

If the compression is *that* low then it's possible that it stalled while the idle was settling down due to the lack of airflow coming into the engine.

Besides that, you're looking at your standard troubleshooting.

Spark, air, fuel. One of the 3 isn't sufficient.

There is definitely something seriously wrong. You can keep wasting your time, but you are just in denial.

Pulled the motor and it turns out that 3 side seals were stuck in their grooves. One partially in the rear rotor, and two almost completely in the front rotor. This is what was causing the low compression.

So now I've started a new thread about what my next steps should be:
https://www.rx8club.com/new-member-f...groove-265532/

Thanks for all your help!

Next step = new rotors and another rebuild. This is why having someone who knows how to determine if parts are within spec is so important. This cannot be said enough.