Hey there,

I have an issue with my 231ps RX8 (manual) 54 plate, (56k miles) and was wondering if anyone has any ideas, as the UK Mazda Technicians are not being all that helpful.

The issue is this:

The car runs fine when cold and on short journeys, however when it is hot and on a motorway or long journey at a constant speed (say 70mph ish) it will begin to loose power and if you drop down a few gears and rev it to approx 5,800 - 6200 rpm, a vibration from the engine will begin (sounds like a flapping or raspy sound) and it will sound and perform awful. If you pull over and let it cool down it will be fine when restarted.

The problem also appears to be much much worse with the air con on, however I would assume that this could simply be that the air con is drawing extra power from the engine and it is just exaggerating the problem.

The car has been back to the dealers about 8 times and so far the following has been changed, most of the parts trying to cure the issue:

New Cat
New Racing Beat Exhaust
New Coils (mazda genuine)
New Plugs
New Leads
New Engine Mounts
New Battery
New Starter
New anti roll Bar
2 * oil Changes

The car has been compression tested and I am told by the garage that it all appears to be fine and well within the parameters (however I have not viewed the figs myself).

The only thing that they have suggested is that the oil metering pump could be on its way out (although when tested in the garage with diagnostics it seemed fine), so that would be the next thing to change. I have been quoted about £1,200 for this job and they are not 100% sure that this will cure the issue.

As you can imagine, I have already spent alot of money on this car and am not prepared to spend another £1,200 on the possibility that the OMP replacement might work. If they were 100% sure it would be more reassuring but they are not.

Does anyone on here have any advice on this situation as Mazda seem to be at a loss and are just changing parts by trial and error.

Any advice or suggestions would be much appreciated.

Thanks

 

That doesn't sound like a OMP issue to me.

There are members here that actually block off the OMP entirely and run without it. They just premix directly into the port via Sohn adapter.

 

I would demand to see the results of the compression test. They can say whatever they want, if they are telling the truth they should have no problem showing you this data.

 

I would like to know the compression test as well.
The oil metering pump may be an issue to be checked. its shaft is made of a pretty light metal and can wear off. A new pump is cheap but they should be able to crank yours up a bit manually. Telling us how many miles you do with 1litre of oil is also a good index for knowing how your omp is performing.
Did they change the coil wires as well?

How's your fuel pump? did you notice power cuts with a low tank in long sweeper turns as well?

Let me know if you need any help trying to sort the omp yourself, it is a pretty easy test to do and WELL beyond the 1200£ mark. Let's say 50$ or so!

Giorgio

 

+1 on this. Ask for the print out and compare it to the chart you can find on another compression thread on the forum.
Make sure you adjust for revs which can vary the numbers.
Your flapping noise/power loss is exactly what I had experienced with mine.
If the deler refuses then take it to another dealer that will give you the orint-out.
Railton

 

fuel pump first thing that would do this.

second as you mention omp.. if it is a very long cruise and the omp underpreforms the apex seals dry out.. the car will run flat, and the exhaust not will change.

but likely it is fuel pump..

beers

 

Thanks for your posts so far everyone.

I think that you are right and I should demand the compression results, however I do not see what the garage has to gain by lying about it as I have an extended warranty on it (which is underwritten by a third party), however the warranty company are refusing to pay at the moment (I am currently challenging this) - This is a very long story and has been going on for weeks now.

Railton - you said that you had exactly the same problem, what was the result and solution? It wasn't an engine replacement was it?

Swoope - you think it might be the fuel pump (along with a few others on this thread), is there any logical reason why it might be causing this intermittent problem? Why would it only be doing it when hot and specifically rattling most at 5800rpm? It happens mostly when the air con is on as well, possibly due to the extra loading, why would this be?

Sorry for all the questions, however this has two Mazda garages baffled and I really need to get to the bottom of it?

Cheers

 

the fuel pump also gets hot then fails after a while.. after it cools it will run fine till it heats up again..

usually takes at least an hour of driving. but that does not expain the rattle you are getting..

beers

 

In both circumstances the "flapping plastic bag in the wind", power loss, poor-er gas mileage, CEL's and compression check led to engine replacements. Full stop.
Spend the $100, and make sure you get a legit printout of the results.
Railton

 

Had the same problem Marbles in a can about 6k rpm and running terribly on a long run in hot weather. All checked same as you and no problems Compression tests all normal . I felt it must have been preignition and ran a can of fuel injector cleaner through the car. Have not had a problem since in any long runs in hotweather .Car idles much smoother and have better fuel economy. Wouldn't hurt to give it a try. If this had failed I was going to pull the SSV out and check it as it opens at about 6k, and this would cause problems if it were sticking.

 

OK so the main sources of the problem are likely to be

1). Fuel Pump
2). Dirty or clogged injectors
3) Knackerd engine
4). Faulty OMP

I would have thought that if the engine was having low compression that you get really bad gas mileage (sub 10 MPG), which I am not and that it is more difficult to start - it starts within half a second to one second usually. When cold, the engine sounds sweet as a nut and pulls hard with no issues. Do you agree that a dodgy engine is likely to be the least likely or not?

The blocked injectors could be an issue and I guess it would not hurt to run an injector cleaner through the system.

Would a faulty fuel pump be causing a rattle at exactly the same RPM (5800 - 6200), which then leads to power loss and noisy idling, until it is left to cool down? I am not doubting what you are all saying, I am just trying to narrow down the options in my own head

Why do some of you think that it is unlikely to be the OMP?

BSE50, you mention that testing the OMP is easy, what method would you normally use to do this?

Thanks again everyone!

 

OK so I went to the garage today to have a new expansion tank fitted (Yeah I had the old coolant warning symbol constantly on again) and I asked for the compression test print out from previous tests.

Long and the short of it, they do not do formal print outs, however they did record the numbers on my file, see below:

@ 320 rpm
8.0
8.0
7.8

@291 rpm
6.8
7.3
6.7

They have recorded these as being normal.

I am not the foremost expert when it comes to the compression of a rotary engine, so what do you all think of these numbers, do they look about right?

Thanks

 

Looks like bad compression to me

 

So what would good compression results look like then?

I cannot see why the dealer would say they are ok, if clearly they are not and if I can get some concrete evidence I will definitely be going back to them.

 

How long is the engine warranty in the UK? Have you tried to decarbon the engine to increase the compression?

 

^ Good point. What is the UK Warranty? There is a DIY Zoom Zoom Cleaner thread that can help you try to decarb the engine to see if it helps. The graph shows a healthy compression across varying rpm's. At 250rpm, you should be getting about 8.5

 

They are looking at the numbers. They higher the RPM the higher the compression.

They think it's like a pistion engine. It's not. It has to be tested at a certain RPM... 250

You have to re-calculate for the difference in RPM.

 

Ok so a further update.

I am still having a bit of trouble with the extended warranty and this is now with a solicitor, however that is another story.

In the meantime I have been doing some testing with the car and have noted the following:

The car seems to run fine and accelerates strongly and smoothly through the rev range even after a long run.

The problems occur as soon as the air con is turned on. When the air con is off you can rev to redline all day long with little noise or rattle, however with a/c on as soon as it hits around 6000rpm it makes a loud rattle and the power drops right off. It also sounds noisier at idle.

Does this change anyones earlier comments?

Could it be an alternator or battery problem, in that with ac on there is a power drain and there is not enough amps to power the OMP or something? I am clutching at straws here as I do not really see why having the ac on makes that much difference.

I originally thought having ac on may just have been exaggerating the problem, however it does not really seem to happen with it off.

Any ideas??

Thanks.

 

This sounds like pre-ignition....It might be what some here call "MIAC" (Marbles In A Can) sound its like shaking a metal can with loose marbles in it. What fuel do you use reg or prem? Please give us the history on your car. The service it's had parts replaced. Type of driving it gets(long commutes, short trip), ever flooded. Just any thing that you can add. Done any decarbon cleaning?

 

Thanks Old Rotor.

I have given the car history and maintenance earlier in the post and it has had many new parts (most trying to cure this ongoing problem). It has been serviced by Mazda every year an has currently done 58k miles.

Never flooded since I have owned the car and definitely not since the Cat, plugs, coils etc were changed. (the problems pre existed the cat change and other listed parts in the first post).

I am in the UK so our basic unleaded fuel is 95RON and this is what I normally use. I sometimes use premium unleaded which is 97RON, however this seems to have very little effect.

I have over the last few weeks been adding Redex to the fuel every fill up, which supposedly cleans the internal system and injectors, however it clearly has not solved the issue.

I have a quick question, if it is pre-ignition as you have suggested, why does the air con being on have this effect. Surely the pre ignition would be present with it off as well as on?

I realise that the ac will be adding load to the engine, which may be the difference, however I just cannot tie up the link.

 

Can you try a couple of fill-ups with a slightly high premix rate?
Like adding 400 grammes per full fill-up to see if the issue softens a bit. I would also try to refill the aircon circuit. It may be partially empty leading the compressor to work improperly.

Anyway your compression results are not within specs so you will probably have to find a new engine anyway. There are some vendors that do good offers for us living across the ocean so that's not an extremely big issue
There are also good rebuilders in the UK but i don't know their experience with this particular rotary.

 

Thanks for the reply BSE.

Yeah I thought the compression was low, however I am not entirely sure the Mazda Tech new WTF he was doing!! It made me a bit suspicious when he said one of the results was with engine cold (the lower readings) and the other when hot (higher readings). This seems a bit odd as I thought it would be the other way around (compression lower when hot) and also I believe you should have six readings and not three at any rate!

Anyways, would compression be giving this effect with the whole a/c issue?

I have read many posts on Marbles in a Can and loss of power and many seem to suggest it happens much more when the temp outside is hot. OK this got me thinking, is it that the ambiemt temp outside is hot that is having the effect or simply that they all have their air con on due to the hot weather???

I am having trouble understanding why having the aircon on would cause a dramatic loss of power, rough idle and a rattling noise at higher revs, it just seems odd to me. I have no problem starting the car (takes about 0.5 secs), acceleration is strong, MPG very good for an RX8, so I would have thought that the low compression issue was not that bad.

Could it be the air con pump vibrating or something and making the pulley not turn properly thereby slowing the car down. This is only a guess as I have not taken these parts off an RX8 before and not sure if they are connected at all in a way that may cause this?

 

I don't think the parasitic horsepower demand of the AC compressor could account for this.

The electrical demand shouldn't be too high; the AC clutch circuit is on a fairly low-amp fuse, iirc, so it's not like it could be pulling 60 amps. If it were a voltage issue, you should get the same results by turning on your high-beam headlamps.

Heat would not seem to be an issue if you are seeing the effect immediately. The added heat load takes time to accumulate.

It would seem that turning on the AC is influencing the engine-management in regards to spark timing, fuel delivery (or opening of SSV?).

Someone with a better understanding of that interaction may be able shed more light. In the meantime, have you tried resetting the PCM and KAM?

 

IF you never have this problem without A/C, it's the A/C compressor. Compressor failures are pretty rare, but can happen. It sounds like it's starting out ok, then with heat and rpm, tries to seize. Once that starts, it's not un-seizing until it cools off. I've also had problems with the pulley clutches that engage the compressor. If the compressor is bad, the clutch is probably bad now too as it's slipping when the shaft tries to stop turning.

 

The A/C compressor could indeed be the problem.

I took the car on a 2 hour run last night with no problems (A/C off) and took it to about 8,500 rpm 10-15 times with no issue at all.

I did do a few DIY bits as well as suggested by other posts:

1). Cleaned MAF sensor
2). Did NVRAM & KAM resets
3). Took air filter out and cleaned leaves and debris out of it (it was pretty dirty on the intake side, so I will be changing very shortly in case there is any possible air restriction from it).

Not 100% sure if any of those actually helped, however I need to test it again with the air con on to see if the problem persists (I would have done this yesterday, however it was getting late and I wanted to get home as quickly as possible without having the problem re appear).

I will do some further testing shortly.