Rb25Det Compression

[Rbvl]

Hey my I just tested my rb25det compression and got

1) 135 psi

2) 140psi

3)140psi

4) 140 psi

5) 140 psi

6) 135 psi

Just want to know if these figures are any good or am I up for a rebuild soon ?

[GTSBoy]

I say ........ more information required.

ie, was it done hot or cold? Was it done with a compression tester that you know DOESN'T read low? Did you try adding any oil after the first set of results? Did you have all the plugs out all the time? How good is the battery?

[SargeRX8]

Do it warm and with another comp tester. Good even results but a wee bit low. I wouldn't fret snd I certainly would not rebuild.

Edited June 18, 2013 by SargeRX8

[phatlavish]

^ that, and make sure the throttle body is wide open

[mungy]

It's not a good result if done hot and WOT,

But its a good result if done the lazy way, ie not getting the engine to temp first, using a fully charged battery and holding the throttle open.

[KiwiRS4T]

Pretty even - should do another 100,000km

[wolverine]

All close enough for me.

[AngryRB]

How many km's? if it has some bolt on mods already then its possible it may have some poncams dropped in, on a previous car i did this and it dropped from 150 down to 115

[Dose Pipe Sutututu]

IMHO, don't rely on actual PSI values, as long as they are all consistent that's what you need to worry about..

[Rbvl]

The engine supposedly has 120k on it. The engine was tested cold because it won't run at the moment I'm putting in a new air flow meter tommoro and hopefully it fixes the problem as it progressively got worse until it wouldn't start. I'm not sure about compression tester i just bought it and it and no I didn't try putting any oil in, I took each plug out individually and tested the plug back in and moved to the next. The battery is brand new so it should be fine.

[GTSBoy]

Right. So, on the basis that the test was not done "correctly", that seems like fairly decent compression numbers. For a cold, dry engine.

Edited June 19, 2013 by GTSBoy

[mungy]

Agreed, cold and dry to hit 140 is a decent result

[mungy]

How many km's? if it has some bolt on mods already then its possible it may have some poncams dropped in, on a previous car i did this and it dropped from 150 down to 115

And wtf? I've never heard that in my life, cams should not affect maximum compression of engine unless you put em in wrong and bent the valves slightly or you forgot to re-shim and the valves are being held slightly open.

[GTSBoy]

Sorry mungy, that's wrong. Big cams cause the static compression ratio (and in fact the dynamic compression ratio as well, except in the middle of the ram tuning region) to decrease because they keep the inlet valves open longer during the beginning of the compression stroke and let a little bit of the charge back out. This is why you can run a higher comp ratio with bigger cams than you can with smaller cams.

Having said that, dropping from 150 to 115 is a bit excessive and would tend to suggest absolutely massive cams or installed too far retarded.

[AngryRB]

Be interesting to check my own engine after the poncams were dropped in, that motor I mentioned was just a Mitsubishi with a reground cam 2mm apparently but who knows.

[Rbvl]

I put a new air flow meter in and it did not fix the problem car still will not start It's a series 2 engine and there are no lights on the ecu and I can't run the fault codes through the dash because it in a vl and there is no light hooked up. I'm thinking it may be the CAS is there any way to check it is working?

[StevenCJR31]

(using standard ecu?)turn the screw on the ecu to diagnostics mode and count the red and green led flashes

this will tell you whats wrong

[mungy]

I put a new air flow meter in and it did not fix the problem car still will not start It's a series 2 engine and there are no lights on the ecu and I can't run the fault codes through the dash because it in a vl and there is no light hooked up. I'm thinking it may be the CAS is there any way to check it is working?

Yes there is a way to check the cas, pull it off and leave it plugged in turn the ignition on and turn the cas with your fingers, if you hear the injectors click it's fine.

[mungy]

Ok so have you done the usual checks? Fuel, spark, timing... Make sure the fuel hoses are on the right way too.

If there is fuel pressure, good spark on at least 4 of the cylinders

[Rbvl]

Well I checked the ecu and there were no LEDs on it but it had 2 loose wires coming from it with tape on them saying check engine light on one and diagnose on the other. When I put the ignition on the fuel pump kicks in but there is no pressure on the fuel pressure regulator showing and I took a spark plug out and looked on top of the piston and it was dry not a sceric of fuel to be seen. Is it normal for there to be no pressure on the regulator until it starts up or should it b there as soon as the fuel pump primes? And yes there is spark on all cylinders I checked that last nite.