S4 N/A rebuild..low compression and no start

[JustJeff]

I'm trying to help a friend out with a S4 in his shop. The history on it is that he had a part-time guy rebuilding the engine for a customer. After rebuild it wouldn't turn over. His part time guy up and disappears on him before the engine issues are resolved. He doesn't know much of anything about rotaries but he pulled the engine and re-rebuilt it thinking his guy missed something. And the car has sat for a year now with no start. He has used Atkins full rebuild kit. I believe he then purchased another full kit for the second rebuild rather than simply replace the rubber seals.

I was out there trying to help him this week, but I have zero experience with N/A engines or even S4. I compression tested the front rotor and got even bumps of 60psi.

Some factors. He has the airpump off the engine, the P/S off the engine, alternator off the engine. He has replaced the fuel pump and coils. He says he has gone through his service software for vacuum diagrams and he think he has vacuum correct. I've made sure that the AFM is plugged in and battery is fully charged and that he is WOT cranking the engine.

I've gotten advice to use some starter fluid and put some oil in through spark plug holes to try to get it to turn over. But is that really going to help if he has 60 psi? Am I missing something simple? He is ready to pull the engine and allow me to re-re-rebuild the engine.

I'll download the S4 service manuals and start doing some research...but any advice would be appreciated.

[JL1RX7]

Hopefully the oil and ATF can build up enough compression to get it to turn over. Even pulses is a good sign that it is sealing somewhat. Make good spark and fuel and see if it fires up.

[need RX7]

Injectors firing? CAS stabbed correctly?

If so; de-flood, put oil in spark plug holes, crank, repeat until it starts.

[JustJeff]

I haven't been over to the car since posting this, but shouldn't compression be higher than 60psi regardless of whether it's turned over yet or not?

[JL1RX7]

What kind of compression checker are you using? I have heard that unless you use a rotary specific one you don't get accurate readings. Now whether that would 90 PSIg from rotary one to 80 PSIg to no rotary is a matter of one's opinion. Since the gauge is reading pressure it shouldn't matter what's producing that pressure. Anyway just some food for thought.

Getting strong even pulses seems to be the deciding factor more than not. It could be the seals haven't "set" completely and a little ATF or oil might help them along.

[need RX7]

Originally Posted by JustJeff

I haven't been over to the car since posting this, but shouldn't compression be higher than 60psi regardless of whether it's turned over yet or not?

Rebuilds usually start off kind of low, especially with used housings. It should come up after running for a while.

I'm not sure if 60psi is 'normal' though.

[RETed]

Hard to say if the 60psi is okay or not...
Unless you baseline that particular compression tester to a known working gauge, it's hard to give you a definitive answer.
I've had compressor testers show 60psi on a newly built motor and end up breaking in okay.

Two things that most people miss:
1) Throttle needs to be propped all the way open - i.e. WOT; I think you mentioned this.
2) You need to remove BOTH the trailings at the same time; Mazda offers specs with both trailings pulled - you can pull both leadings, but the #'s will be slightly lower.

Not doing either or both will reward you with a significantly lower #'s.

The good news is that you get even pulses.
I'd take even pulses over the overall #'s anyday.
There's still a chance the #'s are not a true indication of the condition of the engine, or you can get the engine to break in properly.
If you get uneven pulses, you need a minor miracle to get that to fix itself.


-Ted

[JustJeff]

I've been away from the forums for a little bit of time.

I got the engine to turn over and idle. A little oil in the spark plug holes and some starting fluid sprayed in the intake. It took a little bit of cranking but once it got started it idled just fine. It smoked like crazy, but it idled. I left him to put all the accessories on and give it back to his customer....but then I get a call a few days later and now it won't start again.

So far as I know the only thing he did was put the alternator, air pump, ps and ac, and clutch fan on. Oh and he tightened up the exhaust manifold bolts. He tried doing the oil and starter fluid again. I don't know how much oil he put in the spark plug holes.

I'm wondering a few things. Maybe all the smoke from burning off the oil and starter fluid clogged the cat? Other thing fouled plugs or just plain flooded from him putting too much oil in the housings?

[RETed]

Originally Posted by JustJeff

Maybe all the smoke from burning off the oil and starter fluid clogged the cat?

Not likely...
If it can burn and allow the engine to run, it'll fly right through the cats.
I've run QUARTS of ATF in engines without plugging the stock cats up.
Starter fluid will burn clean.
I've seen blown turbos that'll empty the sump in minutes contaminate the cats but not clog them - it'll cause the exhaust to smoke for a couple hours, but cast still working.

Other thing fouled plugs or just plain flooded from him putting too much oil in the housings?

This is most likely the case.
The spark plugs do NOT like any excessive fluids (oil or gasoline) on the center electrodes.
This area is very porous and just a little bit of oil / fuel will cause a weak spark or eliminate the spark all together.


-Ted