Compression Test Guide - Step by Step instructions

[daelo]

Hi Guys, after been quoted £100 for a compression test (clio 182), after being messed around this morning I have decided that this is a job I should more than likely be able to complete myself, apparently it would have taken them 1 and a half hours to do the test, which seemed wholley excessive considering it normally takes me less than 5 minutes (if that) to get the plenum off to gain access to the spark plugs.

So reading around, there doesn’t seem to be a step by step guide so I thought why not compile one with the help of the experts, which can then be moved to the guide section when complete, so please correct the below where applicable.

1. Car should be up to temperate, 5 – 10 minute drive
2. Remove Plenum/ancillaries where applicable to gain access to spark plugs (10mm socket for machine screws)
3. Unplug each HT lead, making note of the cylinder number and corresponding location on coil pack for refitting
4. Unclip the power source for the injectors so that no fuel is injected into the cylinder (might have to remove the fuel raid guard first 10mm deep socket)
5. Unscrew spark plugs
6. Fit adapter (unsure of what this part is) to the first cylinder
7. Fit compression tester to the adapter
8. Crank (turn ignition on) with throttle open (accelerator pedal fully down even with drive by wire?) for 5 odd seconds until the highest reading is achieved.
9. Repeat process for remaining three cylinders
10. Refit in reverse order from stage 6

How does that lot sound? Is there a special adapter needed for the F4R lump because the spark plugs are buried so deep in the head?

I'd like these steps put into the guide section when we've got it done so it'll help more people like me

 

[mattjk]

yeah i think youve overcomplicated that. lol

1. remove plenum, leads, plugs. pull plug on fuel pump.
2. insert compression tester. crank car, no need for throttle as youve removed the plen-ham.
3. repeat for all 4. put back together

 

[MartinR]

Whats classed as a good/strong reading in psi?

 

[Carlv8415]

Good idea to do a wet test and a dry test.

 

[daelo]

After doing some research, I believe a 14mm hi guage tester will be needed. Decided to go for something of half decent quality (Gunsun Hi Gauge tester 14/18mm), can pick it up from halfords tonight.

For the clio 182 is 190psi regarded as being on spec?

Difference on a wet dry test being a little oil has been spread on the screw thread of the test guage? So best to probably do the test dry first, then repeat by spreading oil on the thread, letting to 'seal' for 60 seconds or so?

 

[jjones82]

Wet test is squirt a little oil into the combustion chamber(10/15mls), it will show if the piston rings arent sealing, only really worthwhile IMO if you get a suspect low reading and want to pinpoint if its the rings / valves etc

 

[Bowsie]

A wet/dry test will tell you if the leak is past the rings or higher up, like past the valves or gasket

 

[jjones82]

Whats classed as a good/strong reading in psi?

From what i've allways been told its not really the reading thats important as long as their consistent across all 4 cylinders (as i've been told that the gauges aren't always the most accurate on non high end compression testers)

 

[Bowsie]

Yes dont waste your time with wet unless you have a cyl that does not reach spec

 

[daelo]

Good , thanks for the above, it's all good stuff for a guide knowledgebase! I'll add that in eventually to the guide part at the top, can anyone confirm or deny 190psi as being a good reading , most likely won't come out to this due to mileage but it's good for reference?

 

[daelo]

Results are in people. Opted to not remove all four plugs at once but rather one by one as i knew i'd get confused and install incorrectly on the return! Also Only took me and hour for the first time doing this (would have been quicker with extension on hose), how the hell can a garage expect to just pull a figure of 1hour 30 for something which is so easy and straight forward, tossers. Un-clipped all parts off the plenum and just removed the power input into the coil, removed the hose onto the throttle body and was able to shift the lot to the side whilst each cylinder was done.

The Gunsun could have done with being a bit longer, I would recommend a reliable means of being able to tighten the hose into the spark plug thread as the holes are so god damn deep, I used a needle nosed pair of locking pliers , to give it a half turn or so on top of just turning loosely by hand, a ratchet spanner with adjustable head would also probably have done it also. Cylinder four wasn't quite tight enough as some swarf blew out, so stopped cranking and re-tightened and got a better reading.

Anyway , the results are as follows from the cam side to gearbox side...

1 2 3 4
182 190 187 182

Are these pretty good readings, admittedly the gunsun isn't going to be the most accurate, but would you say that's a strong engine that's worth investing £700 worth of cambelt/dephaser/waterpump etc? This engine blew a spark plug out in cylinder three 2 years ago which was helicoiled , which has seemed not to have really affected things at all which is good!

 

[daelo]

Anyone good with compression test results care to comment on the above four readings por favor?

 

[JAParker]

anything under 160 I would worry about, so im not a expert by any means but those results look fine, think my were 200 across whole engine.

 

[MartinR]

Mine a couple of years back also read near on 200 across all 4.

Those figures imo seem ok, but im also no expert.

Maybe chipmk1 MicKPM could shed some light on it for you?

 

[MicKPM]

They're pretty precise readings to be taken with a Gunson lol

Not bad readings and within 10% so no need to worry about valve or ring seal issues.

 

[Chip-mk1]

Try without all 4 plugs and it will probably read a little higher as the engine will spin over quicker.

Those figures look acceptable in terms of hardly any variance but pointless comparing to someone else using another gauge when the gunson ones are such terrible quality. I've got 3 gunson gauges and they vary by best part of 20psi between them.

 

[Chip-mk1]

Ps.
You can't really go wrong with the leads as they are numbered on the coilpack which cylinder to go to. And even if you start counting at wrong end (it's Renault so 1 is gearbox end) it will still be fine either way round as it's wasted spark. So 1 in 4 and 4 in 1 is fine as is 2 and 3 swapped

 

[daelo]

Thanks Chip,

I will try again satday with all four plugs out to see if their is any greater variance between readings, hopefully they will still be +/-5 psi at best from around 185, now I best get on the phone to Twotechs/Ren7oaks/Markfish to get some best prices for a full cambelt change! This Clio's going to see 175k+ i can just feel it!