R34 GTT - Compression Issue

[LjB123]

Hey guys. So took my car to a local tuner/mechanic to get it looked over, showed low compression cylinders 5 and 6, they did a leak down test, showed exhaust leak was the culprit. Rest of the cylinders were around 160PSI on average. Only issue i had with the car was with the A/C on, when it was a really hot day, and car was warmed up, when the AC belt engaged/disengaged, the revs would drop a little briefly and before the revs picked back up it dropped enough to stall out, also happened occasionally when going from 3rd to 2nd and i did a slow gear change, the revs would drop and engine would stall briefly until i released the clutch and the engine turned over. With A/C off it wouldn’t do that at all. This particular shop unfortunately didnt have the time to do the work for quite a while due to some race events coming up and the cars they were working on for those, so went to another shop that had a bit of a shorter time before i could get in, and had good reviews. They took the heads off, got it machined, serviced, new head studs, new gaskets, upgraded the valve springs and retainers, upgraded the cams, put it all back together. Theyre now getting about 120-130PSI across all cylinders, car really struggles to start up, and is making only 180kw ATW on 20PSI of boost, and previous owner who had all the work/tune done had 300kw ATW when he got a dyno test done
 

Is there something shonky going on?

How can the PSI drop so bad across the 4 front cylinders that were ok originally? 

Edited February 19, 2024 by LjB123

[GTSBoy]

First up, compression measured on different comp testers is not comparable. You need to use the same instrument and you need to know that its calibration is still basically the same. So the 12-130 you have now could actually be the same as the 160ish that the front four had before.

Of course, it could all be f**ked now, but it's not possible to tell from that measurement alone. The lack of power and so on could be form f**ked up valve timing, boost rags, or a million other awful surprises. 180 wkW is 9 psi on a healthy 25. So there is definitely something very wrong there.

[LjB123]

34 minutes ago, GTSBoy said:

First up, compression measured on different comp testers is not comparable. You need to use the same instrument and you need to know that its calibration is still basically the same. So the 12-130 you have now could actually be the same as the 160ish that the front four had before.

Of course, it could all be f**ked now, but it's not possible to tell from that measurement alone. The lack of power and so on could be form f**ked up valve timing, boost rags, or a million other awful surprises. 180 wkW is 9 psi on a healthy 25. So there is definitely something very wrong there.

One thing i forgot to add in the original post(will update it), was one issue i had with it, was with the A/C on, when it was a really hot day, and car was warmed up, when the AC belt engaged/disengaged, the revs would drop a little briefly and before the revs picked back up it dropped enough to stall out, also happened occasionally when going from 3rd to 2nd and i did a slow gear change, the revs would drop and engine would stall briefly until i released the clutch and the engine turned over. With A/C off it wouldn’t do that at all. 
 

Im just worried, like how could the issues just get so much worse after the engines cracked open and the head serviced and parts upgraded?

Edited February 19, 2024 by LjB123

[GTSBoy]

1 hour ago, LjB123 said:

One thing i forgot to add in the original post(will update it), was one issue i had with it, was with the A/C on, when it was a really hot day, and car was warmed up, when the AC belt engaged/disengaged, the revs would drop a little briefly and before the revs picked back up it dropped enough to stall out, also happened occasionally when going from 3rd to 2nd and i did a slow gear change, the revs would drop and engine would stall briefly until i released the clutch and the engine turned over. With A/C off it wouldn’t do that at all.

This speaks to your idle air control valve perhaps being sticky. Give it a thorough clean.

1 hour ago, LjB123 said:

how could the issues just get so much worse after the engines cracked open and the head serviced and parts upgraded?

The number of ways that people find to mess this stuff up in not limited to those that have already been done. There are always new ways. You need a competent mechanic to do some diagnosis. Maybe one of the things I listed will jump out at them. Maybe they'll find that the last guy to work on it left a dead hamster in the compressor cover, or accidentally filled half the pipework with silicone sealant, or the TB only opens halfway for some reason.

[LjB123]

9 minutes ago, GTSBoy said:

This speaks to your idle air control valve perhaps being sticky. Give it a thorough clean.

The number of ways that people find to mess this stuff up in not limited to those that have already been done. There are always new ways. You need a competent mechanic to do some diagnosis. Maybe one of the things I listed will jump out at them. Maybe they'll find that the last guy to work on it left a dead hamster in the compressor cover, or accidentally filled half the pipework with silicone sealant, or the TB only opens halfway for some reason.

I would have thought theyre competent, they build, work on and tune JDM cars all day every day, including Skylines, they surely cant have made any stupid rookie mistakes. Im already out if pocket $9000 for all the work done, and its worse off than when i started. Atleast the car ran and i could drive it despite the exhaust valve leak. Now its gone backwards 

[GTSBoy]

Well, make them fix it.

[LjB123]

17 minutes ago, GTSBoy said:

Well, make them fix it.

They just called and they reckon its now a bottom end issue. So ive had the top fully refurbished with upgrades, now hes saying it could be the rings, or even a rare chance its a bearing. The cylinder walls arent scored and all looks healthy. Such a crap situation

[Murray_Calavera]

6 hours ago, LjB123 said:

 was with the A/C on, when it was a really hot day, and car was warmed up, when the AC belt engaged/disengaged, the revs would drop a little briefly and before the revs picked back up it dropped enough to stall out

This could be a mechanical issue, but assuming everything is correct mechanically, you could 100% have this issue from a tuning issue (or should I say lack of tuning). 

Fortunately it's quite a simple thing to setup. If you have a laptop and the interest in learning how to tune, I and many others here could walk you through the tuning process so that the car doesn't stall when the A/C compressor engages. 

[robbo_rb180]

5 hours ago, LjB123 said:

I would have thought theyre competent, they build, work on and tune JDM cars all day every day, including Skylines, they surely cant have made any stupid rookie mistakes. Im already out if pocket $9000 for all the work done, and its worse off than when i started. Atleast the car ran and i could drive it despite the exhaust valve leak. Now its gone backwards 

Just because someone works on something and has a workshop does not make them competent...........

Things to look at in regards to Idle and A/C
-Clean and test IACV
_Check that IACV is plumbed correctly
-Check that ECU inputs and outputs are setup correctly for idle and idle up 


Anyone with a laptop calls themselves a tuner these days and there's more to tuning than a fuel/VE and ignition tables.  

You also haven't stated what original work was required. Big thing going from some basic maintenance to ripping an engine apart.

[LjB123]

1 hour ago, Murray_Calavera said:

This could be a mechanical issue, but assuming everything is correct mechanically, you could 100% have this issue from a tuning issue (or should I say lack of tuning). 

Fortunately it's quite a simple thing to setup. If you have a laptop and the interest in learning how to tune, I and many others here could walk you through the tuning process so that the car doesn't stall when the A/C compressor engages. 

It needs a full tune because it now has upgraded cams

[LjB123]

51 minutes ago, robbo_rb180 said:

Just because someone works on something and has a workshop does not make them competent...........

Things to look at in regards to Idle and A/C
-Clean and test IACV
_Check that IACV is plumbed correctly
-Check that ECU inputs and outputs are setup correctly for idle and idle up 


Anyone with a laptop calls themselves a tuner these days and there's more to tuning than a fuel/VE and ignition tables.  

You also haven't stated what original work was required. Big thing going from some basic maintenance to ripping an engine apart.

It isnt his first car hes tuned and done work on. All he works on is JDM cars, occasionally high end european cars like AMG’s and Lamborghinis, and has good reviews from the people who go through his workshop, as well as others ive spoken to. He has checked the IACV and says theres no issues with that.

I mentioned that i took the car to a local tuner/mechanic to look over it, and a compression test was part of it, and that revealed cylinder 5 and 6 had low compression, and when a leak down test was done it had an extreme exhaust valve leak from both cylinders. Not sure what other information you were looking for when asking what original work was required?

Edited February 19, 2024 by LjB123