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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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Bad running after new head gasket - cause?Views : 28736 Replies : 386Users Viewing This Thread : |
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Jan 6th, 2017, 16:42 | #361 |
Rogerthechorister
Last Online: Dec 16th, 2023 02:15
Join Date: May 2006
Location: Rochester
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A thought
A thought occurred to me today (as a result of an EGR pipe problem on my other Sport). The EGR valve opens at about 3,000 rpm doesn't it? Which is why it usually does not affect the MoT emissions. Well, what if there were a crack in the EGR body? Or a big hole in the EGR pipe (one of the two - one goes from the exhaust manifold to the back of the EGR valve and the other goes from the top of the EGR valve to the inlet manifold) that comes from the exhaust manifold. The mixture would suddenly go weak when the EGR valve opened, wouldn't it?
Against this theory, there would be a ticking or blowing noise as exhaust manifold pressure vented through the crack or hole. Views?
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B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold. |
Feb 2nd, 2017, 17:02 | #362 |
Rogerthechorister
Last Online: Dec 16th, 2023 02:15
Join Date: May 2006
Location: Rochester
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Another thought!
Max the mecco says he has tried blanking off the EGR pipe at the exhaust end and it made no difference. But it wouldn't if there was a break in the first pipe section or in the EGR valve itself, would it?
Tuesday she goes to Tim the other mecco to try blanking the EGR off completely. The other funny thing is that Max has been talking to the people in Essex who drift Volvos and they say that there should be a steady voltage on pin 24 of the ECU (which if my memory serves me is the 5 degree retard pin) and we do not have that. I cannot now remember whether we have 12V or zero V (I think it's 12 but I'm not sure - and at about 3,000 or 3,500 rpm it goes to a wobbly 3.5 volts. That MIGHT be a cracked wire in the loom. I don't think it's the crank position sensor as I'm pretty sure we've changed that and if it was the sensor signal then the reve counter would go funny. Some optimism, maybe!
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B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold. |
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Feb 2nd, 2017, 18:50 | #363 |
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Last Online: Today 16:23
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Location: Lakenheath
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If pin 5 should go to 5V and it normally has 0V but at a certain point changes to a wobbly 3.5V then it suggests whatever is meant to switch that input either has broken wiring, dirty connections or the switch/sensor is worn out.
However as this problem occurred after having the head gasket done, i'd be inclined to think this wire got trapped between two metal parts as they were refitted and the insulation has been crushed, allowing some power through but not all of it. If it was 12V and this happened then it would probably blow a fuse somewhere. Usually with inputs that are meant to have a definite voltage on them under certain conditions they work on a "complete change of state" basis, in other words either on or off, not dropping from a higher voltage to a fixed lower voltage. I'd be looking for the sensor that is meant to feed pin 5 with 5V and work back along its wiring to check it's free to move and hasn't been squashed between (for example) the inlet manifold and the head. Many moons ago a friend bought a Vauxhall Senator 3.0 24v for pennies (he got two for about £4-500, one MoT'd but not running, the other a spares car only) because it wouldn't start after having had the head gasket done. The fuel pump feed wire had been trapped between the inlet tracts and the head resulting in a burned out fuel pump relay and a blown fuse. One fuse, fuel pump relay and wiring repair later and he had a highly tuned 24v Senator with no sunroof, wind up windows and cloth upholstery! Oh yeah, it was white as well with some funny zips in the headlining!
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Feb 2nd, 2017, 19:45 | #364 |
Rogerthechorister
Last Online: Dec 16th, 2023 02:15
Join Date: May 2006
Location: Rochester
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Pin 24
I'm pretty sure it's pin 24 - which I think is the pin to put volts on (or is it take down to earth) to retard the ignition 5 degrees.
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B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold. |
Feb 2nd, 2017, 21:12 | #365 | |
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Quote:
Not sure if you'd get away with simply unpluggng the knock sensor to test the theory or if you have a spare one cable tie it somewhere it won't get knocked and plug that one in for a "once only" test to prove the point - just don't go too mad while it's over-advancing with boost or there could be other problems as a result but it should tell you if you're on the right track.
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Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........ |
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Feb 2nd, 2017, 23:23 | #366 | |
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Last Online: Oct 8th, 2022 22:22
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Quote:
The output of the ECU is digital at ttl (transistor/transistor logic) so should be either 5v or 0v (actually around 0.8v). A floating voltage can indicate a fault in the ECU (essentially a transistor is not switching fully "on" or "off") OR that the meter being used is not fast enough to read the signal and is "averaging" a pulsed signal that is swinging from 5v to 0v rapidly. I'm picking the latter. an odd ttl output reading (like 3.5v) cannot be an input sensor problem. As its a voltage signal and effectively has no current, a partial wire fault is very unlikely to cause an error - the current is too low to create a voltage drop and hte singal will still (or should still) be either logic high or low, 5 or 0v. Realistically, the best way to test the output of a logic circuit like this is with an oscilloscope, not a voltmeter. I am guessing here, but I think you will see a high frequency squarewave output swinging from 5v to 0.8v and rms averaging around 3.5v |
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Feb 2nd, 2017, 23:27 | #367 |
Rogerthechorister
Last Online: Dec 16th, 2023 02:15
Join Date: May 2006
Location: Rochester
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But
It cannot be an ECU fault. Three different ECUS are all perfect in my other Sport and duff in this one. And the other point appears to be that pin 24 is an input to the ECU not an output from it. As far as I know. But thank you for the suggestion.
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B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold. |
Feb 2nd, 2017, 23:55 | #368 |
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I've had a good scour of t'internet and i'm guessing your ECU is the one ending in 937 for the B230FT?
The only pinouts i can find are for the B230F (and not the 0 280 000 937 ECU) and it shows pin 24 as an input but only 0 to 1V as it's the signal input from the Lambda sensor. If i could find the pinouts for the 937 there's a fair chance pin 24 would still be an input and probably a logic level (TTL if you will) 5v input in which case my original theory could still apply. Ashs idea about a pulsed output signal could still be but knowing Bosch and how they like to keep certain pins as inputs and certain pins as outputs it's a fair bet it is an input, although not from the Lambda sensor! They're not going to change a whole circuit board just for adding a turbo so altering the input by changing the software and perhaps adding a resistor to drop the voltage or removing a link so the variable voltage from the Lambda goes through a DAC first.............
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Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........ |
Feb 3rd, 2017, 01:18 | #369 |
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if its input from the lambda, it can only swing 1v, not between 5 and 0
http://ipdown.net/jetronic.info/tiki...nector_pin_out |
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Feb 3rd, 2017, 03:00 | #370 |
Rogerthechorister
Last Online: Dec 16th, 2023 02:15
Join Date: May 2006
Location: Rochester
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Lambda sensor
I'll check the ECU number in the morning if I can find the box of bits that has been changed. 937 sounds familiar though. However - - - she had a new lambda sensor during one of the very first attempts (after the head gasket) to cure the misfire. I remember the rueful look on the face of John the garage proprietor - who was a staunch methodist and would never lie or mislead - as he said "When I looked at the state of the old lambda sensor I really thought I'd solved it, but then I put a new one in and it wasn't that".
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B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold. |
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