1996 Mazda 626 Crank no start issue

[GMKV07]

Hey guys, first post here. I'll keep it short, I'm looking to see if anyone else has had similar issues to mine. I have a 1996 626 that I've been working on for a while now, and I have run into an issue that I haven't been able to figure out.

I had some luck in starting up the engine after a lot of cranking at first, and managed to drive it some, but now I can't get the engine to start cold.
It'll crank over fine and I can hear the cylinders firing, but the engine just refuses to start. Fuel pump was replaced and is working, spark plugs and leads are new, battery is new, went as far to replace the MAF and IAC on it too. Not getting any codes either.

If anyone could point me in the right direction it would be greatly appreciated.

 

[200955]

Curiosity compels me to ask if it ran before all this work and how well. Next thing I'd like to know is did you start it directly after each one of these parts you replaced or did you do them all at once and then try to start it. See where this is going? If you have fuel and spark all that's left is air. I remember one time I changed an IAC and there was a particular procedure that required the pintle to be gently pushed all the way into the housing before starting. Then on the first start the ECM would advance the pintle forward slowly until the correct engine mixture (amount of idle air) was achieved. This may be your situation - I am not too familiar with a 626 or if there's a certain procedure when the IAC is changed.

 

[GMKV07]

Curiosity compels me to ask if it ran before all this work and how well. Next thing I'd like to know is did you start it directly after each one of these parts you replaced or did you do them all at once and then try to start it. See where this is going? If you have fuel and spark all that's left is air. I remember one time I changed an IAC and there was a particular procedure that required the pintle to be gently pushed all the way into the housing before starting. Then on the first start the ECM would advance the pintle forward slowly until the correct engine mixture (amount of idle air) was achieved. This may be your situation - I am not too familiar with a 626 or if there's a certain procedure when the IAC is changed.

I did them over the course of a few weeks, delivery time being what it is. The IAC change was due to the fact the previous one had the pintle detached from the motor (I think, the bit that moved up and down was off from the motor) and it did run after that. But even then it required a solid 30 seconds of cranking the engine to get it to start up. Part of me thinks it's a compression issue, the other part thinks that I'm throwing parts at a stupidly simple problem that can be fixed by either sealing up something or the like.

I got the 626 off of some rando's property, got it back home by towing it so it's been a project car for a while. Another thing is that the oil when I changed it smelled heavy of gas so maybe the piston rings are screwed. Might just be one of those cases where I replace the engine in it, as opposed to undoing God knows how many years of neglect it's seen.

 

[200955]

Verify that the compression is good and allow for a compression leak-down test. The values can be found in engine manuals made by all publishers. Pay attention to the differences between cylinders and the acceptable amount of loss through wear of the rings. Although somewhat archaic, these are tough engines capable of very high mileage. Try this: spray a bit of starting fluid into the engine through the throttle body. If it starts chances are you have a good ignition system and it should start even on low compression. Don't go crazy with this stuff but you could actually keep an engine running, once started, with well timed bursts of the fluid. If the engine starts even briefly, it points to a fuel system issue which you are bypassing by using stating fluid. On the other hand if your previous compression test indicates absurdly low compression or pretty much dead cylinders that indicates mechanical issues and doing a test of this type would be useless. If it ran before it should run again.

 

[200955]

I did them over the course of a few weeks, delivery time being what it is. The IAC change was due to the fact the previous one had the pintle detached from the motor (I think, the bit that moved up and down was off from the motor) and it did run after that. But even then it required a solid 30 seconds of cranking the engine to get it to start up. Part of me thinks it's a compression issue, the other part thinks that I'm throwing parts at a stupidly simple problem that can be fixed by either sealing up something or the like.

I got the 626 off of some rando's property, got it back home by towing it so it's been a project car for a while. Another thing is that the oil when I changed it smelled heavy of gas so maybe the piston rings are screwed. Might just be one of those cases where I replace the engine in it, as opposed to undoing God knows how many years of neglect it's seen.

If you don't have a compression gauge, here's a little work around: remove the plugs and with each cylinder at top dead center/valves closed, blast some compressed air in the spark plug hole. Listen for escaping air with the oil fill cap removed which will indicate severe blow-by past the rings, if it's at the end of the tail pipe it's exhaust valves and if you can hear it at the mouth of the throttle body it's intake valves. Be sure each cylinder is at the top of it's compression stroke and the corresponding valves are completely closed. There will always be a bit of blow-by that you can hear but it shouldn't be excessive. To verify bad rings, shoot a bit of oil in the cylinder and again inject air. If the rings are badly worn the oil will go between the rings and the cylinder wall temporarily negating blow-by.

 

[GMKV07]

If you don't have a compression gauge, here's a little work around: remove the plugs and with each cylinder at top dead center/valves closed, blast some compressed air in the spark plug hole. Listen for escaping air with the oil fill cap removed which will indicate severe blow-by past the rings, if it's at the end of the tail pipe it's exhaust valves and if you can hear it at the mouth of the throttle body it's intake valves. Be sure each cylinder is at the top of it's compression stroke and the corresponding valves are completely closed. There will always be a bit of blow-by that you can hear but it shouldn't be excessive. To verify bad rings, shoot a bit of oil in the cylinder and again inject air. If the rings are badly worn the oil will go between the rings and the cylinder wall temporarily negating blow-by.

I'll give it a try, thanks for the advice.