I have a '95 Peugeot 306 dt which has suffered from poor starting for a long time.The car starts, but runs very rough for around 30s from cold.When warm the car drives ok.
After trying and failing to find air leaks in the fuel system,I booked it in with a diesel specialist who has said the fuel system is fine but has diagnosed low compression (270psi) on one of the cylinders.
I have had three quotes from engine specialists to put this right,all around £1000.All of them seemed surprised that the engine should have this fault at a relatively low mileage (88K),but seemed convinced that it was pistons or piston rings.Two of the places said I'd be better off with a recon engine,or getting rid of the car before it got any worse!I'm very reluctant to believe this advice,as surely if it were a piston problem,the car would be burning oil,which it's not?
The garages seemed to dismiss a valve seat problem or cracked head/gasket problem without even looking at the car.Although the oil/water levels are fine and there is no oil in the water or vice versa,which would seem to rule out a gasket problem?? Or could the gasket have blown directly to atmosphere?Would the first job be to check valve clearances?
I'm after some advice as to what people think is the most likely fault,or if there are any other tests I could do to narrow it down,without taking the head off!
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Check the valve clearances
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270psi is not too low. I would of expected fuel to combust at that. What were the other cylinders. Peter
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No1 cylinder:270psi,No2 cylinder:400psi,No3 cylinder:420psi,No4 cylinder: 400psi
I was told all should be well over 400psi, and according to the Haynes manual, the max allowable difference between cylinders is 73psi?? Any thoughts?
(By the way, I think I neglected to mention in the original post that it's a diesel!)
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Yes 270 is low and away from the others but 270 represents 12 or 13 to 1 where diesel is normally ignited and 420 is around 20 to 1 where a diesel become effectient. Where these readings cold or hot, if hot the the 272 will be lower when cold and could give tyou a single pot start up problem but the others should fire up ok if everying else is in place. As you say this could be a piston ring problem of a valve and it isn't going to improve with time. Could be expensive to fix. Regards Peter
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Hello, Peter, this is no real help to Foxy, but I am curious to know how you have arrived at the compression ratios in your reply. I would have thought that they were related to atmospheric pressure of approx. 15psi, which would give the lowest cylinder a ratio of 270/15, about 18/1 and the others about 27/1. Is it because it is a diesel with a turbo? I don't doubt you, I am just interested.
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The relationship between compression ratio and absolute pressure is not linear due to the dramatic heating effect during the stroke and the expansion of the air that is in the cylinder. As you will see from and engines compression ratio and stated comression test it is not one atmosphere times the ration. The real calculation can be found widely on the net and involes, bore, stroke, ration, temp and humidity but I used typical figures to help the guy understand the potential problem. Hope that helps. Regards Peter
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Noticed the typos as I hit' Post'. Sorry for that. Regards Peter
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Further, I think it is a help to Foxi who has a 10 year old car and the cost of repair to a low pot coulf be almost as much as the car is worth so well worth exploring other potential reasons for poor starting including fuel cleaners and flushers incase he has a glued up compression ring. What does Foxi think. Regards Peter
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Thank you. I thought there would be a rational explanation. Good old Charles's law and Boyle's law. Apologies to the ones I have missed.
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Thanks for the advice Peter.
The explaination you give would support the fact that the problem has got much worse in the cold weather. The engine would have been reasonably warm when the compression test was done,as the garage performed it not long after I'd dropped it off to them.
I've tried injector cleaner a number of times,to no avail I'm afraid. Guess I've got a big decision to make. I'm reluctant to pay someone to take the head off,only to tell me its a piston problem. I'd do it myself but I'm worried it would be off the road for too long(The last time I changed a head gasket it took me over 2weeks!). It's a shame as the engine has always ran well apart from this problem.
Do you think it would be worth while checking the valve clearances first??
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270 hot is low as this could be as low as 200 when cold and that is marginal to fire up diesel. You should do a thorough valve clearance check in case the fault lies there but it is not looking too good. Regards Peter
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I still come to thinking why does the car not fire up on the three good cylinders and the poor one kick in after a few seconds. How does it start up and run from cold. ??? Regards Peter
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The car does fire up eventually. It usually stalls immediately after catching the first few times,then runs but VERY roughly, almost as if only firing on two cylinders. After around 20 seconds of chugging and churning out clouds of white smoke it is OK. If I give it some gas straight away after starting it sorts itself out more quickly. When warm it drives OK,but seems a bit down on power I think. The problem has got steadily worse over a 2-3 year period.
Having thought about it,I'm now extremely tempted to do the work myself.
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If you have the know-how, i would be getting the tools out if i were you !
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I just sold my 1995 306 DT for £1680, so I dont think the repairs would outweigh the value of the car! They are good cars, I still havent really taken to my newer 306 HDi yet, it just doesnt have the 'character' of the old XUD engined models. I'd get it repaired if I were you!
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I think I will get it repaired. It will set me back a lot more to shell out for something new and its still in great condition apart from this problem.
I'd like to think I had the know how(I changed the head gasket on my old Rover Metro)it's just finding the time! But I guess I have nothing to lose. Has anyone here had the head off a 306dt before?? Is it a particularly tough job? It doesn't sound it according to the Haynes manual.
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It is not partially tough, just awkward. I would give yourself a day to remove head if you have not done one before. Because it is such a big lump there is no room. I find the two hardest things were removing the guards around the timing belt and removing the exhaust manifold (I did not remove the turbo, bolts were seized solid)
Be aware of the Haynes manual wording, the word ?manipulate? is often used, this really means it is going to be a right git, avoid taking to it with the large tool to hand.
If you are pretty hands on it should not be too much of an issue. As bits start to come off, just keep them in an orderly fashion.
Notes, the head bolts could be either of the ?posi? type or a standard socket, I have done two head gaskets, one was one and one was the other. But both sets of the stretch bolts were ?posi? (excuse spelling, not too sure, but I?m sure you know what I mean)
(Have you tired the old oil down the cylinder trick during the compression test? It?s a bit cowboy-ish, but if the compression increases because the oil makes a better seal you can be more confident that it is a ring.)
Let us know how you get on. I?m sure my compression is low with 160k+ but I really do not want to find out for sure!!
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Cheers hm.I dont own a compression gauge unfortunately, otherwise I would have considered trying the cowboy method!Might be useful to get one as I've also been told you can tell if its a valve or ring problem by how the pressure builds up on successive strokes.
Having looked at the room around the timing belt I'm anticipating some grazed knuckles. This is the only bit I'm worried about. Well, that and the fact that half of the bolts will round off when I try to undo them! Can you leave the turbo in place and still remove the exhaust manifold then??
Think I'll start by checking the valve clearances this weekend then take it from there. I'll keep you posted.
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You can lift the head with the turbo and manifold attached, just undo the downpipe and the turbo' oil pipes from the block.
Couple of things worth noting if you are going to attempt yourself as it catches people out time and time again.
Bolt through the engine mount to cylinder head, once removed there is a spacer that sits partially in the head as well, takes a bit of tricky wangling but it comes out. Also there is a bolt holding the metal pipes below the brake servo pump. A lot of people miss these and thn get frustrated.
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Thanks, I'll keep these things in mind when I start. Probably wont start yet as its not really the weather and I only have access to a single garage.
Just another thought, once I've got the head off, if it is not obviously head gasket or a valve problem, what is the best way to check the pistons/rings? If it does turn out to be a problem in the cylinder block I guess its engine out time. All the more reason not to pay a garage to remove the head I suppose!
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Could I once again urge you to check the valve clearances before taking the head off.
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Just to give an update:
Checked the valve clearances this afternoon. All of the exhaust valves were crack on (0.30mm), but the clearance on all the inlet valves was <0.04mm, when it should be 0.15±0.05mm.
This has confused me even more. I half expected the valve clearance on the cylinder with low compression to have closed up, but not all of them! I'm surprised the car runs at all. I can't understand how I'm getting good compression on three of the cylinders if the valves are being held open??
Can anyone help me out with an explaination please?? Does it indicate that the head needs overhauling??
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The inlet valves are larger in diameter and therefore more prone to recessing themselves into the seat. However this small clearance will still allow the valve to close but later then required so some compression may be lost. This small clearance may reduce to zero when hot so set them all up and try it out berfore deciding whether to take the head off. Regards Peter
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I`m sure Peter is correct about re-adjusting valve clearances as a first step - and that theses will change as the engine warms. Had a similar problem with a Ford 1600 pinto some years back - the no.3 inlet valve on these engines is hard to adjust without taking the carburettor off, so most mechanics just don`t bother; produces similar symptoms, but not so bad; engine ticks over on 3 when hot.
Agree about XUD engine - daughter had the later Peugeot diesel, a disaster at 80,000, the very professional mechanic I have known for years said it was a dog, hated them - can`t remember the name - XED? - no doubt all you Peugeot buffs can ID whatI mean.
Regards, and good luck!
AS
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