McGoo

Hi Guys

I have a 2008 series 1 RX8, the engine in my 8 was low compression, readings on a normal tester were around 80-85 PSI and it used to start from cold on the key and get warm and just stop, Ive had the engine rebuilt and compression is 90-100PSI, I know the normal compression testers are not that reliable an indication but I'm getting very even pulses across the faces of each rotor and I understand the compression will increase some more when I can get it to drive.

The car will not start from cold on the key at all, if I pull start it, it will run great but not idle then as soon as it gets to normal temperature, it will stop, when it stops there is no spluttering, and no throttle response, it stops as if the ignition or fuel has been cut off suddenly, when it is running it revs smoothly, no unusual noises and no smoke at all. You can pretty much set your watch as to how long it will stay running from a pull start.

I have spark and fuel and was wondering if it could be to do with the fuelling as my understanding is 2 of the fuel injectors are for normal running and the other 2 are used for starting/idling, mine is a 192 low power version, all connectors are in place and using the snap on scanner, no DTC's are present, I had one initially for the oil metering pump which put the car in limp mode and the CEL on, I swapped out the OMP and it is fine now.

I have checked the coil packs according to the Mazda FSM and they check out and the fact the engine quits suddenly, I would have thought if it was dodgy coils I would get a misfire rather than a sudden cut off?

Also the EPS is not working, it was fully working before, the previous owner had removed the connector under the airbox tray and soldered the wires, all connectors have been cleaned and the fuse is ok and battery terminals tight.

All input appreciated.

alnielsen

iTrader: (4)

Normally a warm start problem is associated with low compression. And, that would be the reason the engine won't start. It seems that you have been taking compression readings with a conventional compression checker. These don't work well with a rotary engine. They don't measure each face of the rotors and you may be testing at the wrong RPM. Unless you know a mechanic that has a rotary tester, you will need to take the car to a Mazda dealer to get the compression check performed.
Other areas you can check are in the ignition system (spark plugs, wires and coil packs). Another possibility is the fuel pump is bad.
The soldered wires under the air box are likely to be for the power steering. The previous owner must have had some problems with the connectors at one time. This is common and there are a range of ways to fix it. One being soldering the connections.

McGoo

Thanks, I'm going to look into the fuel pump/system more, releasing the fuel cap is creating a whooshing noise, need to find out if its pressure or vacuum, the pump is operating briefly when I first put the ignition on, will work through the fuel system tests in the FSM.

McGoo

Fuel system checks out ok, Ive seen conflicting opinion on how the ignition system operates on here, I found one thread where someone stated that for starting the ignition fires the trailing plugs, also found a Mazda service bulletin where it states that the car starts on the leading plugs and the trailing are inop, can anyone confirm?

bse50

Who did the rebuild?

McGoo

Just had all the plugs out and connected to the leads and even with a battery charger on boost start, the sparks all start out bright blue then deteriorate after a few cycles so I'll try new leads and coils.

McGoo

I did, why?, The issue is not with the engine, its within the ancillaries, I suspect coils, have ordered replacements.

bse50

Do another compression test.
It started despite its low compression before the rebuild...

McGoo

I have as stated in the OP, compression is higher than before the rebuild!

bse50

Compression alone means nothing! the whole disassembly\assembly\engine bay relocation process is tricky

McGoo

Really, I found it quite straightforward with the Mazda literature available online, mind you I did have workshop facilities, would have been more time consuming doing it on the driveway like some people have done.

bse50

It is straightforward, nobody denies that. It's just that there are many things that might go wrong during a rebuild that it's hard to judge or fault a single component over a computer.
What we know is that the car had low compression before the rebuild BUT it somehow started.
Now it has slightly higher compression (still almost sub-par) yet it doesn't want to start.

That's why i'd argue over the whole rebuild process before pointing any particular component. Worn coils and plugs won't prevent a solid engine from starting!

McGoo

I'm going to replace the coils anyway, I've had the plugs out and earthed them one by one while turning the engine over while connected to a booster and I'm getting only a couple of bright blue sparks on each before they fade considerably.

McGoo

Fitted new coils, started straight away off key, idles perfect and suspect the cutting out is either bad battery or alternator issue as it will run without dying whilst connected to external power, as soon as that is turned off it cuts out

Phoenix_

Have you measured the voltage when the car is running?

McGoo

Yes, was 14.4 while running, was running fine for about 40 mins, switched aircon on and it died.

dynamho

even on 'external power' as you stated?

McGoo

Yes