Jump to content
SAU Community

Recommended Posts

Hey guys , recently i dynoed my car and after the dyno, i did a engine compression test and the numbers were pretty bad compared to 2 years ago ~ which was around 130 across all 5 cyclinders except for the 2nd cyclinder which is 100. But after adding some oil on the 2nd cyclinder, the compression on the 2nd cyclinder immediately jumped back up to 125 psi. So they concluded that the injector in the 2nd cyclinder is faulty. But after asking few other workshops, they are saying injectors and low compression rates are unrelated..

any ideas guys ?

Thanks

injectors are before the valves. The oil let the loose rings in cyl2 seal better which bumped up the compression, temporarily. If they added oil to the other cylinders they more then likely would have jumped up much the same, so across the board would have been something like 155.

Surely all the oil is doing is sealing the rings better which means that's what's no good in that cylinder. If the test with oil didn't go up then you would be looking at valves. That's my theory anyway.

Surely all the oil is doing is sealing the rings better which means that's what's no good in that cylinder. If the test with oil didn't go up then you would be looking at valves. That's my theory anyway.

thanks for the replies guys, so is it safe to say its unrelated and irregardless if the injector is faulty or not adding oil will bump the compression readings up ?

thanks for the replies guys, so is it safe to say its unrelated and irregardless if the injector is faulty or not adding oil will bump the compression readings up ?

Unrelated with injectors mate .

You are correct abo .

If a little amount of oil increases comp it means rings and or bore worn but don't forget a substantial amount will increase comp because the combustion chamber is smaller because of the oil . In a low comp cyl if puting oil in to it doesn't increase comp it means the valves are leaking.

Do a leakdown test as well.

leakdown test is the best test to do.

Remove the sparkplugs, remove the intake and oil cap do your test. if its intake valves and there is reasonable leakage you'll hear/feel it coming out the intake, same for exhaust if its piston/rings you'll hear/feel it coming out the oil cap. just make sure that each cylinder is firing TDC (top dead centre).

Its a good idea to turn the motor over a few times once spark plugs are removed just incase theres any foreign matter between the valve and the seat which will give a false reading.

leakdown test is the best test to do.

Remove the sparkplugs, remove the intake and oil cap do your test. if its intake valves and there is reasonable leakage you'll hear/feel it coming out the intake, same for exhaust if its piston/rings you'll hear/feel it coming out the oil cap. just make sure that each cylinder is firing TDC (top dead centre).

Its a good idea to turn the motor over a few times once spark plugs are removed just incase theres any foreign matter between the valve and the seat which will give a false reading.

Thanks guys for the replies, im sending my car in for the leakdown test tommorow. Will see how it goes and check out what is the problem

Cheers

Thanks guys for the replies, im sending my car in for the leakdown test tommorow. Will see how it goes and check out what is the problem

Cheers

HEy guys, got my leak down test and compression test done today. results were

Compression test Leak down test

cyc 1 : 155 10%

cyc 2: 155 20%

cyc3 : 155 5%

cyc4: 153 5%

cyc 5 : 150 5%

cyc 6 : 151 5%

looks like all went well and will be proceeding to the next mods :domokun:

Thanks for the feedbacks

HEy guys, got my leak down test and compression test done today. results were

Compression test Leak down test

cyc 1 : 155 10%

cyc 2: 155 20%

cyc3 : 155 5%

cyc4: 153 5%

cyc 5 : 150 5%

cyc 6 : 151 5%

looks like all went well and will be proceeding to the next mods :domokun:

Thanks for the feedbacks

That indicates bore and or ring wear on number 2. and to a lesser extend in number 1 as well .

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 know why it happened and I’m embarrassed to say but I was testing the polarity of one of the led bulb to see which side was positive with a 12v battery and that’s when it decided to fry hoping I didn’t damage anything else
    • 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.
×
×
  • Create New...