trulite

Hi guys, I just joined today and am really finding my way round here, also i cannot post

I really need some HELP!!!

I have a 04 MT 85k with uprated starter motor. I just had the engine rebuilt in Nov 2013 and went back to get a compression test a few months ago and it was reading around 90psi for both rotors. At the same time i was having hot start issues and the mechanic told me since my compression was good it had to be my coils and leads etc as I didn't have original ones in.

Anyway the other day i bought a new set of coils original from Mazda and Magnicor 8mm HT leads. Then done the brake pedal test 20 times to reset. But it still wont start on hot start up. When i floor the car it sort of judders around 7 - 8k revs and then if i leave my foot off the accelerator it cuts off straight away.

It starts up cold fine but i have to wait at least 45 minutes to start it again. Also I have been running the car very low on fuel and once i ran out completely!! Silly me!!

Now i have to park it on a hill so i bump start it. I am cleaning the corrosion on the battery terminals today and checking the batt.

Please Guyswhat do you think is wrong with my 8, could it be the fuel pump!! i AM NOW SPENDING ALOT ON IT.

Thank you so much and i really appreciate all yourt help guys .

RIWWP

iTrader: (2)

(Moved from the other thread you posted in)

Looks to me like you can post just fine.

Perhaps you are referring to the thread creation limitations discussed in this annoucement at the top of this subforum: RX8Club.com - Announcements in Forum : New Member Forum

Also in that annoucement list is a link to this thread: https://www.rx8club.com/new-member-f...t-here-202454/

Which has a compression chart that shows that 90psi is failing with a cranking speed of 230rpm or higher, so your mechanic's statement that "compression is good" is an incorrect statement if your starter is average or better.


Who rebuilt the engine? What all did they replace?

At a guess, I'm guessing that just the seals were replaced, but not the other worn parts, and you ended up with a an engine destined to die again in relatively short order.

trulite

Hi thanks for the fast reply, really appreciated it. Maybe I have the wrong numbers but I have attached the print out of the actual test. Please let me know if this is okay.

The mechanic done a full rebuild I have attached the invoice with full details. As I am a Noobie i'm scared he could be taking me for a ride but he has really good reviews on Face book. So really came to you guys for help. LCRotary Invoice LEWIS 10009 b (1).pdf

trulite

Once again thanks.

RIWWP

iTrader: (2)

Logalin:

No, I've seen the wave form test before, also with an odd random PSI number in the center left of the chart. Here is a more recent post showing it: https://www.rx8club.com/new-member-f...3/#post4601070

As with that one, I don't believe that the PSI number indicated there is part of the chart's scale. I don't know what it IS, but it isn't the scale. The top of the chart is 200psi, the bottom 0psi, the heavy line exactly halfway is presumably 100psi. Each horizontal line is then 12.5psi (1/8th of 100)

Still...


trulite:
Yes, that is showing a failed engine. The peaks are just about at, or a bit under the first line under the middle line, so that tells me that each rotor face is in the range of ~85psi-88psi. The peaks are about 1.4 lines apart (vertically), which corresponds to about 250-260rpm cranking speed. When normalized, that is going to be 6.1-6.2 kg/cm2 range, when 6.9 and lower is failing at 250rpm cranking speed.

All rotors are suprisingly consistent, which tells me that my prior guess is probably accurate. You probably have new seals, but re-used housings and irons, so low compression all around.

If the mechanic doing the test doesn't know to use a rotary compression tester, I can assure you that he doesn't know enough to rebuild a rotary. You lost out on paying for that rebuild, but it still needs another.

Read this post: https://www.rx8club.com/new-member-f...4/#post4533733 (link jumps down to the right post) and the post immediately after.

logalinipoo

Hey pearl, i realized that. The number on the left is based on the vertical line in the middle if the chart. It looks like that line is moveable so you can place it on a peak and see actual pres verses estimated from the graph.

RIWWP

iTrader: (2)

Good catch. Makes sense.

trulite

My mechanic said that the middle line was 100, he also said that he thought the numbers were okay. I do have a 12 month warranty with the build and have until Nov to get it fixed again. What if he checks it again and the numbers are the same do i say that's way too low. ??

Cheers.

RIWWP

iTrader: (2)

The fact that he says that they are fine now means he doesn't know what a good engine should look like. The numbers are already failing, he can retest, but it will still fail. If he is really interested in getting a good test, then he needs to do the test with a Rotary Engine Compression tester. Your local Mazda dealer should have one.

He needs to look at the factory service manual, learn what he needs to do with normalizing the results to 250rpm at sea level

Point him to the new owner's thread with the explanation if you think it would help.

trulite

Thanks .... really appreciate your help. I will get my car in and ask him to rebuild it again as last time he said it was my coil packs etc as they were not original now ill ask him what the problem is asi've changed them!!! I am also taking your post with me with the numbers you gave ie 6.9 lower being a failing engine.

Once again thank you.

RIWWP

iTrader: (2)

Not just numbers. He needs to understand that a rotary engine is different from a piston engine in regards to many thing, but specifically compression scores. The RPM really does matter, because an engine that is passing at one RPM may be failing at another RPM at the same pressure score.

If he doesn't have the factory service manual for the RX-8, it's available for free here: Foxed.ca - Mazda RX-7 Manuals

And it even has a calculator for normalizing the scores: Foxed.ca - Rotary Compression Calculator

RIWWP

iTrader: (2)

If he does rebuild it, he will really need to make sure he rebuilds it to spec, and ANY part that isn't in tolerance needs to be replaced. The seal clearancing can also make a large contribution to how good the engine is, so he will need to make sure he does it properly. It's a simple engine, but very easy to screw up on a rebuild.