Help! 2x Engine Failures due to Low Compression in Rear the Housing
 

Hi all,

I have just lost my second engine(within 1000kms) due to evenly low compression in my rear housing.....

I bought my car December last year and within 2000kms of driving, it started to push coolant out the overflow tank.. which lead to my first rebuild in May this year. This involved all new every thing except the rotors so big $$$. After getting my car back it ran fine for the first 100kms then started to sound like it was heavily ported at idle (Its a mild turbo port) being the run in period I thought maybe it had some thing to due with the tune. So after running it in I took it back to my mechanic to tune.

When I pulled up to his shop, he looked at me very startlingly and said it sounds like it's running on 1 rotor at idle? The car spent the next week at his shop whereby he tried to fix the strange idle issue, he initially didn't think it could be a compression issue because it made really good power on the dyno (210kws @ 7psi) and secondly it was a brand new motor with only 1,200kms.

The issue wasn't solved so I got a compression test done, the front rotor had 110-109-110psi, the rear had 60-58-60psi....... it was strange because under power the car felt very good, none the less I gave the car back to my mechanic for the 2nd rebuild.

At this stage the car had been built by another shop a few years ago, and my mechanic/tuner didn't want to take any of the work for granted so we changed/ checked a few items. He believes the only thing that could make the rear seals evenly lose compression like that would be either from lack of oil/ or fuel.

So after this I had my ID injectors tested, FPR tested, fuel pump Checked, oil lines/ squirters replaced with new items, new apex seals (E&J), Innovate AFR installed. My mechanic wasn't familiar with the ECU so I swapped it out for an Adaptronic Ecu which can control the OMP.

2nd engine rebuild is complete and its idles perfect, and runs awesome, 150kms in the run in period and the 1 rotor at idle is making its way back............ I immediately take the car back to my mechanic who then replaces a the OMP with a reconditioned unit. I then finish my break in period all under 4k RPMs and the engine sounds like it has built compression, for the 1 rotor sound has nearly disappeared.
I get the engine compression tested and its 110psi in the front housing and 90psi in the rear, the seals had damaged slightly, evenly again but no were near as bad.

I then take it to the track (WTAC) after getting it retuned and the 1 rotor (low comp) sound is back..... just as bad as before. Which gets me to today, where I don't know what to do.

Has any one experienced this before? I have spent so much money and time in the last year and barely been able to drive my car.

Sounds like it might be time to get dual wide bands or dual EGT's so you can correctly dial in some extra fuel on the rear rotor/figure out whats happening...
Really, you should not be needing to do that though. Are you confident in your tuners abilities?

Maybe try a simple changing of the plugs and see if it clears up. It it does it may simply be fouling prematurely for some reason. Incorrectly configured OMP maybe.

Also, just for info's sake.(not saying your previous engine wasnt toast) but pushing coolant out of the overflow tank is not always blown coolant seals. It could also be that the system is not recovering coolant back in after it gets warm (and there are several reasons for that, including bad radiator cap or hose from overflow to filler neck not holding vacuum)

PS. We got you in the finals mate!

You wouldn't believe it, I had the 2x EGT's ordered they arrived the day after the engine was put back into the car.......

My mechanic/ tuner is Ric Shaw, he has been building rotors for 35 years and he pretty much only uses adaptronics, he was involved in their development. I took the car to another tuner after the first engine issue, and he didn't see the need to adjust Ric's setup.

After it pushed coolant out of the overflow tank a few times, I got my hands on a TK combustion gas tester, it changed from purple to dark green....:(

I am very excited to watch this match, its at 5am Sydney time so I will be pretty sauced as well hahaha

What EGTs are you seeing?
Are you premixing?
What air/fuel ratios are you seeing?
Did you check the seals for warping?
What were the seals clearance to?


A complete list of your setup would help.

EGT were too late to get installed........

Yes I am premixing, 500ml of oil per 60 litres in conjunction with the OMP.

A/F Ratio is seeing anywhere from 13.5 down to 11 or even 10.

The seals from the from the first build looked okay to the eye actually, but it was probably very minor bowing.

They are a 2mm seal, not entirely sure of the clearances, I would need to ask my mech. '

List of Engine Mods
- Engine fully rebuilt, new everything bar rotors
- Precision 6266 turbo
- 3.5 turbo back
- Front mount Trust intercooler
- ID1000 Pri ID2000 Sec
- Walbro E85 460l fuel pump
- Turbosmart 1200 FPR
- Under driven pulley set
- Adaptronic ECU running individual coils

What apex seals are you using? Lay them down on a true flat surface and see if they rock. Then stack them all together and see if there is any light gap between the seals. Do the same stacking the seals end to end.

Having fun yet?

I'd be looking at your secondaries first up. E85 track experience with them out here, at least, isn't the best, you might ask your other tuner why they were fuel trimming during events. :nod:

Logs > post-mortem.

I was using physco seals and now I'm using e&j seals, just got the car comp tested today, it doesn't look good, less than 43psi in the rear chamber

I only run pump fuel, the car has only seen about 7 minutes of track time. I had 2 tuners look at my tune, they both said the trim was ok in the rear. the rear naturally runs considerably hotter, it has been a gradual loss of compression so it's hard to pin point the cause through logging.

Talk to me about your engine harness.

and you might consider a break in period.

How's it go, riddle inside a mystery, ha....:scratch: Suppose that front mount wouldn't have done the water temps many favours on the hot Friday, but 7 mins = 3 or 4 laps basically.

Goodfella's idea might be worth a follow up. Mark would have done the initial black box install with whatever splicing required out at Girraween. With the number of crimped shared earths in these, sparky warned me not to mess with 'em.....possibly cheaper to empty the wallet further and buy another S8 harness than troubleshoot?

Can't remember your manifold - with that turbo, did run into boost cuts presenting themselves...not replicated during dyno ramp of course!

I had a similar issue with a motor that was built years ago with an aggressive street port and out of spec side housings. The apex seals would see too much heat and they would bow. Would drive fine until after break in and on the dyno it would slowly lose more and more compression. Happened 3x in a row after rebuilding the same motor.
The builder should be looking closely that everything is in spec.

Its still oem for the PNP Adaptronic.

I have done at least 1000kms below 5K for my break in periods.

I will buy a s8 harness then.
I may even look at replacing the rear rotor and new housing. I am even tempted to buy a second motor and plugging that in.

I am also thinking of tearing the car apart and selling it, then buying a s15. Its getting really hard to justify spending so much.

That sounds exactly the same to whats happening to me!

Certainly getting beyond a joke with potentially a 4th engine in less than a year, although I know of at least one bloke who has gone through more!

If you want a full on endurance race car - and upgrade to open class, Mark Stinson did have a well developed S15 for sale a little while back....more power than your typical 13b can sustain for extended period on track too.

I do remember seeing the installation of the Black Box in a R32, all the flying leads needing termination certainly looked like potentially a shorting hell if not done properly, do they have a record of install....or is it an ex-owner job possibly? Seems something fundamental, doubt Ric would miss step wear, neither he or Evan are dropkicks either.

That s15 is sounding very tempting right about now.

Evan gave me the details of the autoelectrician who installed the black box ecu, that's who I got to uninstall it since he would be most familiar with it.

I have sourced a second hand engine harness already! I'm just wondering if I should order a new one...

Out of spec side housing. I agree.

Sparky here did like the idea of a new harness (S6), but it wasn't his money! They were only about $600 out of japan, at that stage too, not $1000 as now, with all of Mazda's price increases.

If it's not totally cooked, usual issues are primary injector and CAS plugs, which are available, even if the colour isn't quite right, depends on how much money you want to throw down the hole I guess.

Could you explain to me the out of spec side housing?

I know the face of the housings were diamond lapped during the initial build, are you saying that they could be out of tolerance now?

Or the port is slightly off causing excessive heat in the rear chamber?

The guy with a second hand harness quoted me $250, seems pretty reasonable, if not yeah I will be looking at 1k. I would almost be better of getting a new Ecu with a wire in loom?