starting problem - 4TL 850

[Tripyrenees]

Symptons - started to run a little lumpy but with choke slightly out it was OK. Starting prgessivley got harder, but thought it was due to becoming colder here. Then finally it did not start at all, after a short run (1km) to the supermarket. Towed it home.

What I have done so far;
1. Changed condenser - no change
2. Tried a second coil - no chamge
3. Cleaned and set gaps on all spark plugs
4. New set of points with gap set - no change
5. Check spark at coil, before spark plug and at spark plug - all good but no change
6. Removed carb and took thelid off, cleaned all jets with compressed air.
7. Checked feul squirt when pedal pressed- all good but no change.

What is next to check. This problem came on progressivley and now nothing. It does not even try to fire. A little bit stumped here (distributor and hence, the timing, has not been touched and is all tight)

Thanks in advance (this is my son's daily driver)

 

[André4Renaults]

The spark is good at the plugs, so, if the points are set right & the timing is correct then that's the electrical side (hopefully!) sorted. Is it possible that the petrol has become contaminated in some way? Valve damage would occur at once, not gradually, so that should be OK. Could it be that the head gasket has blown? The symptoms suggest it might be; loss of power, engine running unevenly, becoming difficult, if not impossible to start.

Just before Christmas-that's all you need!

 

[malcolm]

Unlikely to be the head gasket. You'd know about it long before it stopped the car from starting. Same for engine damage.

For the bad running is the air intake pipe in the winter position? That can cause bad running at this time of year. (But wouldn't explain failure to start).

Sparks find it more difficult to spark with compression and fuel than when you test them outside the engine. Worth checking the condition of the distributor cap, especially if the carbon brush at the top is still in place and it's spring still works. Equally if there is an earth wire in the distributor on that model earthing the plate the points are mounted on to to the distributor body it's worth checking that. HT lead from coil to distributor cap too.

Which carb do you have? It is unusual to see a 850 carb with fuel squirt. Is the choke operating correctly? Was there fuel in the float chamber when you removed the top?

Worth checking the timing even static - line up the notch on the flywheel with the notch in the hole on the gearbox and see if the points are just opening.

I take it the battery is OK and the engine is turning over quickly enough.

 

[Tripyrenees]

It is the standard carb, I just meant the feul is coming in when pedal pressed. There was plenty of feul in the chamber.

Will check the timing tomorrow.

I was going to check compression tomorrow when the battery is recharged, what should I expect?

Thanks for the help so far, it is just a pain really as my GTL ( the wife's daily runner is also poorly too)

 

[mojobaby]

hi tripyrenees, after repeated attempts at starting, your spark plugs should be wet with fuel, but only if fuel is getting through obviously.

last year i had a similar problem; uneven running, stalling at traffic lights, difficulty restarting etc.
i found that the bolt at the base of the carb had worked loose, allowing air to be sucked in. i tightened it and a month later it worked its way loose again.

So I was basically sucking too much air and not enough petrol, hence the need for the choke.

if you've checked that and found it to be tight, check the bolts are tight on the manifold at the cylinder head and the gaskets as well.

 

[Tripyrenees]

OK here are the results of the compression test

1 - 9
2 - 11.2
3 - 10.5
4 - 12

The anode on No1 spark plug looks a little cooked.

Also, there are a few irregular burps and back fires out of the top of the carb

Manifold is getting warm with a good 60 seconds of engine turning using the starter motor. But it does not seem to want to fire at all.

 

[malcolm]

Sounds like the ignition timing is way out. Is the cap located in it's notch and the ignition leads on the right way around?

 

[Tripyrenees]

Yep, just checked it all - just bought some new spark plugs and leads. Put them on but no change.

Checked what mojobaby said and found a nut off the inlet manifold, put a new one on and tightened them all up. It started but sound terrible, just a chug chug sound and when any gas is given it cuts out.

Pulled the spark plug cables off one by one while engine ticking over, 1 no change, 2 engine cuts out, 3 engine sound smoother, 4 engine cuts out.

What next, possible valve issue? - remembering this was a progressive fault that ended up with no start or engine run.

 

[André4Renaults]

If you pulled off HT lead one & nothing happened then it's not doing anything! Cylinders 2 & 4 seem to be doing all the work and 3 is working against the engine. Are you quite SURE the timing's in order and that the plugs are on the right leads?

 

[Tripyrenees]

They match the haynes manual

 

[André4Renaults]

They match the haynes manual

Sorry, I wasn't suggesting you'd made an error. This is a strange one! Did you check that all the plugs were sparking? If No. 1 is sparking normally it suggests a lack of compression, confirmed by the reading. Cylinders 2 & 4 have HIGHER compression & ARE working properly, hence why there engine stops when the leads are disconnected. Cylinders 1 & 3 are where the problem lies, but I suspect you'd worked that out yourself! I shall have a "think" over Christmas & see if inspiration strikes.....

 

[chudson]

You should try compression test after adding some oil into cylinders(30-50ml ) just to know if the weak compression on cylinder 1 is due to piston rings or gasket/valves dammage.
Check nay leaks under the carb ( are there any vacum hoses on this engine ? )

 

[Tripyrenees]

No worries, I had to question it myself. I think I will take the head off and take a look but not tomorrow

 

[Tripyrenees]

Right - the head is off, stripped, cleaned and the valves honed in. No4 had some slight pitting but not so bad. But the inside was coked up like crazy. The oil paths in the rocker shaft were pretty blocked up to.
Head is all fitted back together ready to be put on the engine tomorrow with a new head gasket (happened to have a complete gasket set in my drawer). No4 piston is also a bit coked up compared to the others too ??

Will keep you updated.

 

[chudson]

You haven't checked the piston rings ?

 

[mojobaby]

it's worth while checking that the choke plate at the top of the carb hasn't stuck in the closed position. If you give a little gas, it might be flooding with not enough air coming through the top. Sorry, it's just a wild theory!
Also check that your breather pipe on the rocker cover isn't clogged

 

[Tripyrenees]

So what is the easiest way to check the piston rings without taking them out. The compression was not so bad but not equal across the 4 cylinders. What should I expect to see.

I cleaned out the carb on the bench, blew it out with air and fuel. Seems OK. Will check the breather pipe and clean it all out before I put it back on the car.

Just to say when I took the rocker cover off, the top of the head was just a black gooey mess. The rockers themselves did not seem to move easily and the valves were not fluid within the guides. There was so much crud in there. I am hoping it just needed a clean up and resetting of the tappets. fingers crossed.

 

[mr-reno-139]

You may be lucky but if oil has been neglected to the point of turning into a solid mess the internal oil galleries inside head and block will most likely be blocked
I would try soaking whole head in a bucket of diesel fuel for a few days and striping rocker shaft down not easy on 845
You can also use it poured in bores and will give you a n idea if rings are sealing
The danger you face is if any lumps of solidified oil were disturbed when you took head off and drop into sump picked up in the oil strainer you will destroy engine if it restricts flow to oil pump
So either drop sump and clean out or hope for the best depending on your abilities to completely rebuild or replace engine

 

[chudson]

So what is the easiest way to check the piston rings without taking them out.

As i mentioned before you took the head off. The easiest way is to check compression after putting some oil in every cylinder. If the pressure leaked through the pistons the oil would seal it for a while and the compression test would show improvement. If the valves caused the problem the oil wouldn't help and the compression would still be weak.

 

[Tripyrenees]

OK - I think the oil lines are OK, the head is totally cleaned and the rocker shaft is rebuilt (totally silly design ). A lot of sludge in the bottom of the block which explains the overheating issue in busy traffic. I will try and dissolve this out when the engine is back running asI don't won't to get the crud into the oil chambers.

Will let you know - It may end up taking the engine out as it does look a little tired and I have not touched it other than water pump before.