Lambda, Manifold And Compression

[DeeeeC 0]

Hi,

 

 

some questions I have - please help my car is in bits and my second MOT test failed again on emissions. Mechanic suggested injector as gas test gave lambda of 1.17 and HC of 26 ppm and could barely read and CO - like 0.0 at fast idle, 0.3% at idle. Also said could be a post cat exhaust leak.

 

1) what is normal pre-cat lambda voltage? Web says it can be between 0.1 and 0.9 volts. I am getting 2.2V pre cat and 0.38V after cat on FES - I rewired the harness to no effect.

 

2) what is normal compression for a 2.0L CF3 JTS engine? I get for cylinders 1-4 respectively:

230, 220, 235, 245 in psi - it seems high, but this is no loss of coolant or oil. Plus my compression guage broke when the cylinders fired a little due to the compression.

 

3) How do i take off my intake manifold without breaking anything or getting a high pressure shot of fuel to the bloodstream? I took off the fuel relay and coilpacks and turned the engine for 30 seconds. I can see three bolts on the aluminium part of intake at the top. I took off the pairs of hose clips to each cylinder - but don't want to break the plastic part of the intake. I have to check and clean the injectors.

 

 

This seems to quickly be turning into an engine rebuild and I don't want to go that far - when it's in bits you feel like changing everything while you're doing it!

[Smaky 73]

I think ambition is outdoing ability here, on 2) HOW did the cylinder fire? if you've got a guage in it then ther is NO ignition, pressure wise I would expect 160 PSi, your figures just don't match so I'd say the guage is knackered.

 

The plastic part of the manifold is held on by 4 bolts, a 13mm at each end and 2x 15mm bolts in the center, all are underneath, the wiring is then all in clips and needs to be releasesd too.

[DeeeeC 0]

Thanks Smaky.

 

Ambition is a bit high today. I think my high lambda voltage can only be caused by the heater shorting to the sensor, i.e. knackered?

 

I'll change the guage. I have no clue how the cylinder fired there was no coilpack! That's when the guage broke. It sounded like it fired for a second and bust the check valve on the guage.

[DeeeeC 0]

OK,

 

I finally got the time to work on this again after some work priorities.

 

The answer to how the cylinder fired with a tester in it. Well, from my thread on water and white spirit for decarbing the engine, it became clear there was a lot of coked up crap in there that raised the compression to 245 psi on cylinder 4 when it should have been about 160 psi. Now consider the JTS is about 11.3:1 compression ratio. A 2.0 JTDm diesel engine compression ratio is 16.5 to 1. Scaling up the proper JTS compression ratio to 16.5:1:

 

(160 / 11.5) x 16.5 = 230 psi

 

This means that if I pumped in diesel fuel into the (previously) coked up 245 psi JTS engine of mine, the compression alone without a spark could fire the cylinder. The fact that it was petrol made it a lot more volatile and easier to ignite with compression alone and is why my tester broke.

 

So at least that puzzle is sorted out now. If my new compression tester shows the engine is not damaged we now know that my engine has done at least 20k miles (obviously the compression built up pver the life of the engine) at this compression of 245 psi without damage implying that if someone had the inclination - there is scope for forced induction. According to the scaling above for compression it seems the engine can handle 50% more compression, so half a bar of boost that would equate to 50% more power or going from the claimed stock of 165 BHP to around 220 BHP. But I'm not going to try that!

 

I'm going to post a guide on how I got my manifold off once I'm through cleaning my injectors and refitting them. It was a colossal b!tch of a job so now I know what you meant.