Engine compression

In a Cabriolet GTI of the 91 DX engine, the fuse of the fuel pump, is the number 15?
I want to do the engine compression test and for that I want to disconnect the pump.

Can you tell me how the ignition is switched off?

I think the compression ratio is 10: 1


thanks for your comments

Just disconnect the ht lead from the coil and turn the car over on the key.


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Surely unless you disconnect power to the pump it will still inject fuel? 5th injector definitely will.

Yes but won’t fire. Why is the little bit of fuel a problem?  


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Not a problem, just wanted to clarify it (partially to confirm my own understanding).

You only turn it over a few times until you hit max pressure then unscrew and move to the next one. Only an issue if a catalytic converter is fitted to the car as they don’t like neat fuel but you won’t have one of them.  


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Backinblack said

You only turn it over a few times until you hit max pressure then unscrew and move to the next one. Only an issue if a catalytic converter is fitted to the car as they don’t like neat fuel but you won’t have one of them.   Sent from my iPhone using Tapatalk

I had read that it is better to disconnect the gas pump, although in other cars I had not done it. Thanks.

You could pull out the fuel pump relay from the fuse box if worried...

I have already done the compression test.

This is the result with hot engine.

Order of the cylinders: 1,2, 3,4

(Kg/cm2)  13,1 – 10,3 – 12,5 – 12-5
(psi)            187 – 145 – 178 – 177

Whit oil
(Kg/cm2)  14,5 – 13,5 – 14,8 – 14-5
(psi)             206 – 191 – 212 – 205

What’s your opinion? The segments of the pistons in bad condition, especially cylinder number 2?


Thanks

Yes No.2 is low compared to the others, I guess it depends on what plans you have with the car…. It will probably drive fine for a few years if you go carful but if you have the time and money it might be worth pulling the head off to see what's wrong, might just be the gasket is failing?

Always fit new gaskets and valve stem seals as the rubber goes hard over time and it's a lot easier when the heads off.

Could be as simple as Pulling the head,  drop the sump and pistons out.  Use a flex hone to clean the bores and cross hatch them, fit new rings (mic'ing them)  replace the valve seals new head gasket sump gasket…..Valve cover gasket… while you have the pistons out you can plastigauge the mains, and replace if needed be mindful of the thrust bearings (Mark all Caps, and pistons.) then you will have rebuilt the engine sort of and your compresion number will or should be closer…



You are sort of within specs.

I'm going to control oil consumption, and depending on the result, I'll see if I follow your advices.

For me, the worst thing is the smell of burnt oil.

Briano1234 The engine DX it's de same to as the JH?

probably not but the issue is the same that one cylinder is out from the other 3.  Yall have some crazy engine spec over there.

90's over here were all JH

my late green clipper is JH , fitted with catalyst, very similar to dx, but different… vac pipes etc.  very odd ive got 4 cabby 3 gti and 1 clipper all injection and each has differing layout in engine bay.  nothing seems to want to swap over….

with check did you repeat a couple of times? to to get an average?  if within 10% of each other its normally fine.
Your readings like mark/briano says are showing issues on no2, but depends could be sticking rings or worn.  Bad running can be variety of things, breather gauze blocked, dodgy leads, ht leads, my garage didnt remove the adaptors on plugs and as such the HT leads was sparking across.
But no harm in planning to remove and check, get gasket kit with head bolts and cylinder hone, minimum. At least its running.

Try putting a little oil in No2 getting it around the edge of the piston then repeating the test, if your compresion increases significantly  there is a problem with rings, bore whatever, if it stays the same then it could be valves, gasket, etc.

Looks like Nerja in the background of your car?

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Haha yes … I think I saw similar car last summer maybe I photo and shared it.  On the side street next to the old brick work

I used to live in Torrox. My mates garage still has two cabby shells on his roof, round the back of Lidl. I think there's probably still a few bits there, I'll have to pop over and have a look.

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