Jump to content
SAU Community

Recommended Posts

Just want to confirm something about doing a compression test - havent gotten an answer in the ancient DIY thread i bumped in the tutorial section (i guess under general maintenence is a bit more browsed than there) so hopefully I can get a faster answer here as i plan to do this tomorrow.

Basically just want to double check something with the procedure. One user suggested that unplugging the crank angle sensor will prevent spark AND fuel injection - is that right?

So would i be right in assuming I could

- disconnect CAS + coilpack loom (which will be out because the spark plugs are out anyway i guess)

- depress accelerator fully for WOT

- turn key as if i was starting the car until gauge needle stops moving

- repeat with small amount of oil for a wet test

Or will I have to unplug other things/remove fuses etc?

Link to comment
https://www.sau.com.au/forums/topic/313714-diy-compression-testing-qn/
Share on other sites

just start up your car with the fuel pump fuse disconnected, then wait for it to stall.

crank it for a few seconds after that.

now remove your coils and spark plugs.

stick your tester in cyl 1 and crank for a few seconds under full throttle and get the reading.

repeat for cyls 2-6...

just start up your car with the fuel pump fuse disconnected, then wait for it to stall.

crank it for a few seconds after that.

now remove your coils and spark plugs.

stick your tester in cyl 1 and crank for a few seconds under full throttle and get the reading.

repeat for cyls 2-6...

ok sweet, fuel pump fuse is the top fuse in the boot of an r33 right

err 5th one i mean

Edited by errno
and if you are genuinely worried....just save yourself time and start at cylinder 6 not 1....

not really worried, just changing the spark plugs so i figured id do this at the same time and make sure everything is actually sweet before i start spending money on other mods, then only to find out something is going to go wrong :thumbsup:

Cyl 1 is the front of the engine where the radiator etc is right?

yeah cylinder 1 is at the front, and cylinder 6 is where at least 50% of failures happen if you suspect a problem.

it doesn't matter if the other plugs are in or out (there is no connection between individual cylinders except the crank shaft) but with them out watch out for the 150psi air shooting out the spark plug hole!

yeah cylinder 1 is at the front, and cylinder 6 is where at least 50% of failures happen if you suspect a problem.

it doesn't matter if the other plugs are in or out (there is no connection between individual cylinders except the crank shaft) but with them out watch out for the 150psi air shooting out the spark plug hole!

the air coming out of the hole won't be at 150psi. that is just the pressure that will build up if there is something blocking it.

the reason for removing all the spark plugs when doing a compression test is so you get an accurate measure of each cylinder individually. if you have spark plugs in the other cylinders then they will be building pressure on their compression stroke which may lower the reading you get because the engine will be turning over somewhat slower.

the air coming out of the hole won't be at 150psi. that is just the pressure that will build up if there is something blocking it.

the reason for removing all the spark plugs when doing a compression test is so you get an accurate measure of each cylinder individually. if you have spark plugs in the other cylinders then they will be building pressure on their compression stroke which may lower the reading you get because the engine will be turning over somewhat slower.

ok got it =)thanx

sweet thanks for the help guys

got it done, decided to do 2 dry tests (just incase i did something wrong on the first one because ive never done it before) and a wet test

on first test got

1:174 2:172 3:171 4:171 5:171 6:171

second time got

1:172 2:172 3:170 4:170 5:169 6:168

tried to to a wet test, put a tiny pit of engine oil into cyl 1, put in the tester and turned it over but the guage started to read up to like 200 psi so i crapped myself and stopped - then tried to crank it again and it wouldnt crank over at all only the fan would start up, nfi what happened so i just threw in the new plugs put it all together.

it started up ok after this but it did blow white smoke out the exhaust for a while, hopefully it wont blow smoke next time :S

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I came here to note that is a zener diode too base on the info there. Based on that, I'd also be suspicious that replacing it, and it's likely to do the same. A lot of use cases will see it used as either voltage protection, or to create a cheap but relatively stable fixed voltage supply. That would mean it has seen more voltage than it should, and has gone into voltage melt down. If there is something else in the circuit dumping out higher than it should voltages, that needs to be found too. It's quite likely they're trying to use the Zener to limit the voltage that is hitting through to the transistor beside it, so what ever goes to the zener is likely a signal, and they're using the transistor in that circuit to amplify it. Especially as it seems they've also got a capacitor across the zener. Looks like there is meant to be something "noisy" to that zener, and what ever it was, had a melt down. Looking at that picture, it also looks like there's some solder joints that really need redoing, and it might be worth having the whole board properly inspected.  Unfortunately, without being able to stick a multimeter on it, and start tracing it all out, I'm pretty much at a loss now to help. I don't even believe I have a climate control board from an R33 around here to pull apart and see if any of the circuit appears similar to give some ideas.
    • Nah - but you won't find anything on dismantling the seats in any such thing anyway.
    • Could be. Could also be that they sit around broken more. To be fair, you almost never see one driving around. I see more R chassis GTRs than the Renault ones.
    • Yeah. Nah. This is why I said My bold for my double emphasis. We're not talking about cars tuned to the edge of det here. We're talking about normal cars. Flame propagation speed and the amount of energy required to ignite the fuel are not significant factors when running at 1500-4000 rpm, and medium to light loads, like nearly every car on the road (except twin cab utes which are driven at 6k and 100% load all the time). There is no shortage of ignition energy available in any petrol engine. If there was, we'd all be in deep shit. The calorific value, on a volume basis, is significantly different, between 98 and 91, and that turns up immediately in consumption numbers. You can see the signal easily if you control for the other variables well enough, and/or collect enough stats. As to not seeing any benefit - we had a couple of EF and EL Falcons in the company fleet back in the late 90s and early 2000s. The EEC IV ECU in those things was particularly good at adding in timing as soon as knock headroom improved, which typically came from putting in some 95 or 98. The responsiveness and power improved noticeably, and the fuel consumption dropped considerably, just from going to 95. Less delta from there to 98 - almost not noticeable, compared to the big differences seen between 91 and 95. Way back in the day, when supermarkets first started selling fuel from their own stations, I did thousands of km in FNQ in a small Toyota. I can't remember if it was a Starlet or an early Yaris. Anyway - the supermarket servos were bringing in cheap fuel from Indonesia, and the other servos were still using locally refined gear. The fuel consumption was typically at least 5%, often as much as 8% worse on the Indo shit, presumably because they had a lot more oxygenated component in the brew, and were probably barely meeting the octane spec. Around the same time or maybe a bit later (like 25 years ago), I could tell the difference between Shell 98 and BP 98, and typically preferred to only use Shell then because the Skyline ran so much better on it. Years later I found the realtionship between them had swapped, as a consequence of yet more refinery closures. So I've only used BP 98 since. Although, I must say that I could not fault the odd tank of United 98 that I've run. It's probably the same stuff. It is also very important to remember that these findings are often dependent on region. With most of the refineries in Oz now dead, there's less variability in local stuff, and he majority of our fuels are not even refined here any more anyway. It probably depends more on which SE Asian refinery is currently cheapest to operate.
    • You don't have an R34 service manual for the body do you? Have found plenty for the engine and drivetrain but nothing else
×
×
  • Create New...