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Author Topic: Low compression on one bank. Not an Omega.  (Read 2529 times)

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Migv6 le Frog Fan

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Low compression on one bank. Not an Omega.
« on: 22 October 2020, 23:06:04 »

A flat 6 not a V6. What are the possible causes of all three cylinders reading 120psi while the other shows 180psi.
Car has a constant cam sensor fault code, despite cam sensor being replaced. Seller seems to think the cam sensor the cam sensor fault code could cause the ECU to alter the cam timing, thus giving low compression.
I dont see how thats possible when the cams are driven by chains from a shaft, which is driven by another chain from the crankshaft.
Seller seems very genuine by the way. Just maybe a bit out of his depth.
https://www.ebay.co.uk/itm/Porsche-Boxster-1997-2-5-Ocean-Blue-Manual/324344800085?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
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Nick W

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Re: Low compression on one bank. Not an Omega.
« Reply #1 on: 22 October 2020, 23:15:06 »

If it has variable valve timing, then the cam sensor fault is likely to be reporting a fault with the variable mech. Changing the sensor doesn't fix the fault, no matter how many times you pray it will.


Buying a Boxster you know has a fault that extensive work didn't cure is, errrr, brave :o
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Re: Low compression on one bank. Not an Omega.
« Reply #2 on: 22 October 2020, 23:29:39 »

You're assuming that the chain that drives the chains that drive the valves is in the correct place...

Especially if you have low compression across a whole bank.

Brave is an optimistic choice of words :D
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Re: Low compression on one bank. Not an Omega.
« Reply #3 on: 23 October 2020, 03:41:44 »

Reading the advert,, buy it if it gets to much Break it
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Re: Low compression on one bank. Not an Omega.
« Reply #4 on: 23 October 2020, 07:40:56 »

Pretty sure these were known for headgaskets and heads cracking.....

If it is, removing the sludge from the system will be worse than an Omega
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Marks DTM Calib

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Re: Low compression on one bank. Not an Omega.
« Reply #5 on: 23 October 2020, 07:47:34 »

Well the fault code is pointing at the wiring harness, not the sensor.

This could of course, assuming it does have VVT, result in reduced compression.

But no sensor change is going to sort it!

This car has had to many idiots who don't know what they are doing pissing around with it
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Migv6 le Frog Fan

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Re: Low compression on one bank. Not an Omega.
« Reply #6 on: 23 October 2020, 08:25:55 »

I have dug a bit deeper into this. The Car does indeed have VVT.
I think Mr DTM could well be in line for a cigar on this one, as almost everything has been tried, and the only sensible suggestions have come from people who know about these cars, suggesting some kind of wiring fault.
Could be a needle in a haystack, but depending how high the bids go, I might just have a bid on it.
Depends how brave Im feeling when the auction is ending.  ;D
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Migv6 le Frog Fan

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Re: Low compression on one bank. Not an Omega.
« Reply #7 on: 23 October 2020, 08:53:45 »

The only example I found of the same problem online, was on a US forum.
After much messing around and pulling out of hair, the owner found the loom at the rear of the car had been damaged by a bodyshop.  :y
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Marks DTM Calib

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Re: Low compression on one bank. Not an Omega.
« Reply #8 on: 23 October 2020, 15:29:44 »

Thing is, if you know the basics about DTCs and how they are raised, understanding DTCs becomes MUCH easier.

At the end of the day the ECUs can only determine a few things, is the signal plausible (within a defined range), is it open circuit (broken connection somewhere), is it connected to ground, or is it connected to battery.

The DTC states that the interface shows the connection is seeing a voltage which is at, or close to, Vbatt (battery voltage).

Now a short to batt is almost impossible within a sensor, it can only really occur in a loom.

What's the betting garage one were fixing something and have, as a result, stuck something through the loom and its shorting to Batt voltage or they damaged the loom and its doing similar.

I would expect there to be only three or so wires to the cam sensor so hardly a large number to check (and easy to measure with a DVM whilst measuring for resistance to battery)
« Last Edit: 23 October 2020, 15:39:19 by Marks DTM Calib »
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henryd

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Re: Low compression on one bank. Not an Omega.
« Reply #9 on: 23 October 2020, 16:58:39 »

Thing is, if you know the basics about DTCs and how they are raised, understanding DTCs becomes MUCH easier.

At the end of the day the ECUs can only determine a few things, is the signal plausible (within a defined range), is it open circuit (broken connection somewhere), is it connected to ground, or is it connected to battery.

The DTC states that the interface shows the connection is seeing a voltage which is at, or close to, Vbatt (battery voltage).

Now a short to batt is almost impossible within a sensor, it can only really occur in a loom.

What's the betting garage one were fixing something and have, as a result, stuck something through the loom and its shorting to Batt voltage or they damaged the loom and its doing similar.

I would expect there to be only three or so wires to the cam sensor so hardly a large number to check (and easy to measure with a DVM whilst measuring for resistance to battery)

Or bolted something up and pinched it in a joint or similar ???
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Re: Low compression on one bank. Not an Omega.
« Reply #10 on: 23 October 2020, 18:14:18 »


What's the betting garage one were fixing something and have, as a result, stuck something through the loom and its shorting to Batt voltage or they damaged the loom and its doing similar.

I would expect there to be only three or so wires to the cam sensor so hardly a large number to check (and easy to measure with a DVM whilst measuring for resistance to battery)

Or bolted something up and pinched it in a joint or similar ???


On a Porsche(or any high-end German car)? With all that room to work, and with the loom slack calculated in microns? Let alone the German engineer's ability to inly see complex solutions
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Marks DTM Calib

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Re: Low compression on one bank. Not an Omega.
« Reply #11 on: 23 October 2020, 20:53:46 »

Thing is, if you know the basics about DTCs and how they are raised, understanding DTCs becomes MUCH easier.

At the end of the day the ECUs can only determine a few things, is the signal plausible (within a defined range), is it open circuit (broken connection somewhere), is it connected to ground, or is it connected to battery.

The DTC states that the interface shows the connection is seeing a voltage which is at, or close to, Vbatt (battery voltage).

Now a short to batt is almost impossible within a sensor, it can only really occur in a loom.

What's the betting garage one were fixing something and have, as a result, stuck something through the loom and its shorting to Batt voltage or they damaged the loom and its doing similar.

I would expect there to be only three or so wires to the cam sensor so hardly a large number to check (and easy to measure with a DVM whilst measuring for resistance to battery)

Or bolted something up and pinched it in a joint or similar ???

Unlikely, that generally gives a short to ground  :y
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henryd

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Re: Low compression on one bank. Not an Omega.
« Reply #12 on: 23 October 2020, 23:09:55 »

Thing is, if you know the basics about DTCs and how they are raised, understanding DTCs becomes MUCH easier.

At the end of the day the ECUs can only determine a few things, is the signal plausible (within a defined range), is it open circuit (broken connection somewhere), is it connected to ground, or is it connected to battery.

The DTC states that the interface shows the connection is seeing a voltage which is at, or close to, Vbatt (battery voltage).

Now a short to batt is almost impossible within a sensor, it can only really occur in a loom.

What's the betting garage one were fixing something and have, as a result, stuck something through the loom and its shorting to Batt voltage or they damaged the loom and its doing similar.

I would expect there to be only three or so wires to the cam sensor so hardly a large number to check (and easy to measure with a DVM whilst measuring for resistance to battery)

Or bolted something up and pinched it in a joint or similar ???

Unlikely, that generally gives a short to ground  :y

True enough :y
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Re: Low compression on one bank. Not an Omega.
« Reply #13 on: 23 October 2020, 23:51:07 »

People are bidding silly money on it. Auction fever I suppose.  ::)
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Re: Low compression on one bank. Not an Omega.
« Reply #14 on: 24 October 2020, 11:04:11 »

They all think it’s an easy fix ;D
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Re: Low compression on one bank. Not an Omega.
« Reply #15 on: 24 October 2020, 11:11:26 »

Does it have oil pressure relief valves on each head? Could be a faulty one staying open on that side  keeping the lifters open?
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Re: Low compression on one bank. Not an Omega.
« Reply #16 on: 24 October 2020, 19:54:18 »

Plus everyone on eBay is as thick as 2 short planks. Buyers and sellers.


//TB muffles under his breath due to another idiot on their buying something and then within 15 mins asking if it can be cancelled because he doesn't want the item for days/weeks, which leaves me out of pocket on the Paypal fee. Fickwits.
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Re: Low compression on one bank. Not an Omega.
« Reply #17 on: 25 October 2020, 18:23:28 »

Made £2800. Did you get it?

Lovely colour.
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amba

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Re: Low compression on one bank. Not an Omega.
« Reply #18 on: 25 October 2020, 18:44:15 »

Lot to pay with those issues although expect it could make almost that in parts
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Re: Low compression on one bank. Not an Omega.
« Reply #19 on: 25 October 2020, 21:08:56 »

The most I would have been willing to pay for it would have been £1500. I thought it might reach two grand.
Someone who either knows exactly whats wrong with it has bought it, or someone who knows how much they can sell the bits for.
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Re: Low compression on one bank. Not an Omega.
« Reply #20 on: 25 October 2020, 22:02:07 »

 :y
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Re: Low compression on one bank. Not an Omega.
« Reply #21 on: 26 October 2020, 13:48:28 »

The most I would have been willing to pay for it would have been £1500. I thought it might reach two grand.
Someone who either knows exactly whats wrong with it has bought it, or someone who knows how much they can sell the bits for.

Either that or some poor soul has made a horrible mistake!  ;D
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