Mates RX8 - almost starts

[350matt]

Gents

one for the collective
a chap at work has bought a Rx8 for the princely sum of £600
its a 231 with about 60K on it and he did a compression test before buying and its all in the 6's and its a bit tatty but otherwise complete
however
it will only start with a jump battery connected otherwise it merrily cranks over at 250rpm and 'almost' catches
it will on occasion fire up without the extra battery / jump cables but this is a rare occurrance

in trying to solve this it has had a new battery, new plugs and the MAF and ESS have been cleaned

a known good set of coils have been substituted to no avail
battery voltage during cranking is 10.5V and 12.5V with the ignition on

there appears to be no or negligible ( 0.02amp) current drain with the ignition off and the car locked

oh and fuel pressure has been checked and is at 4 bar

your thoughts gents?

[bigpete8]

Only thing you haven't changed for starting is the starter motor...

[Davemitch]

Spark plugs maybe?

[warpc0il]

Main body earth point?
Follow black cable down from battery

[Paul_13]

Does sound like possibly an earth issue. Have you checked the condition of the battery terminals?
I found that the standard rx8 battery clamps are crap, they weren't actually clamping the battery despite being fully tightened

[bigpete8]

[V8 Power]

I know a lot of people pack the clamps out with a flat piece of lead or other supple metal.
I opened up the clamp faces and filed them away to reduce the clamp size. Worked for me.

[PeteH]

I like your Chinese puzzle. "I've covered everything you can think of, and it still doesn't start. Explain...."

Here's my list, in no particular order:
- Earths
- Are the HT leads breaking down? Do they make good contact at both ends?
- Are the HT leads & coils on in the right order?
- Has it has a burp? Is the intake and the MAF free of oil?
- Is the air filter 60k miles old?
- Is the wiring to the coils in good condition (no shorts)?
- Are the fuel injectors clean? Is the wiring to them in good condition?
- How does it run when it does start (lumpy and mis-firey, or smooth and silky)?
- Is the fuel in the tank more than 6 months old?
- Is the 4 bar of fuel pressure actually at the fuel rail, or at the pump? If at the pump, is the pressure reaching the rail (check pipe runs)?
- Is the pcm upset by some sensor issue? (maybe the IAT or ECT is reading wrong, and making the engine think it's a hot start)?

Or something else....

[SteveTroman]

any codes coming up?

[boosted]

Collaspsed cat?

Sent from my SM-N950F using Tapatalk

[Paul_13]

Collaspsed cat?

Sent from my SM-N950F using Tapatalk

Not sure if it would be that.

The car won't start without a jump pack connected which says to me it has a crap connection to the battery

[350matt]

thanks for the replies gents

battery connections have been packed out with some shim steel already
not checked but don't think there's a cat in there as its very eye watering on start up ( when it does start)
will update

[boosted]

I was just adding to Pete comprehensive list

Sent from my SM-N950F using Tapatalk

[350matt]

So update time

it now starts normally - Huzzah!

however the mystery is that nothing else has been replaced since the last time
the only thing is the spark pug / coil testers / flashers where fitted and then removed and the MAF sensor connection has been cleaned

so its possible a plug lead wasn't on properly or something else was disturbed

hopefully it wil now get batter the more he uses it

[350matt]

OK and now its not starting again.......

I've advised him to try swapping around the ECU relays and fuses and if that doesn't help then its a case doing a continuity test on all of the wiring loom between ECU socket and sensors

[Lemon]

What coils are fitted to it?

Sent from my Nokia 6.1 using Tapatalk

[ChrisHolmes]

Is it kicking at all when trying to start it and is it spinning fast enough. Check it’s not flooded and if it is then whilst the plugs are out dry them on a gas ring or under the grill,

[350matt]

So a bit more digging has found that then the big wire between the battery positive and the alternator has been rubbing on the chassis and belt so its in a right state with half the core exposed ...

so next step is to replace that with new parts and then see how it goes

[350matt]

What coils are fitted to it?

Sent from my Nokia 6.1 using Tapatalk

its got a recent set of Mazda C spec's on it and a known good set has also been tried that makes no difference

[Lemon]

What coils are fitted to it?

Sent from my Nokia 6.1 using Tapatalk

its got a recent set of Mazda C spec's on it and a known good set has also been tried that makes no difference

Rules that out then, was wondering if 585's were fitted as have heard of problems with the adaptor harness for them.

That alternator feed could well be grounding out and causing all sorts of electrical woes.

Sent from my Nokia 6.1 using Tapatalk

[350matt]

Hopefully yes

he's working on it a little bit at a time as he has no garage and is currently stripping out the old toasted wire about 20 mins each evening

come November he might have it done

[jas128]

Hi just been reading your post im having same problems did you get to the bottom of it yet cheers jas128

[350matt]

Yes thanks once the main power wire between batt and starter was replaced it turned over better and then had to remove plugs to remove all the fuel
and after that was then sluggish to start so we tried a better starter motor and now its fixed

so in summary the following was wrong with it
1) air / vacuum leak on a split intake hose
2) shorted out starter motor power wire
3) dodgy chinese starter motor

putting this lot right seesm to have done the trick and from the end of the month its being pressed into daily use

[jas128]

Hi glad to hear its good news will check these out thanks for the info cheers

[350matt]

Hello Jas

did you already replace the battery on yours?
if not then measure the voltage across it when cranking
it should be at least 10V
if not then chrage it up and try again
if its still lower than this then replace it

and how fast is it cranking?
if you plug in a scan tool to the OBD port and use the 'datastream' function you should be able to read off the rpm
these cars don't like starting with much less than 220rpm and to be honest the 14 tooth starter upgrade is worthwhile on any of them