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.