Process of Elimination

[bullzed]

Hey everyone,

 

well the engine in my 280 is playing up AGAIN. After the last problem was sorted the car seemed to be running fine, the only problem was that the timing was off despite being fully advanced and the oil pump had to be taken off to readjust the distributor shaft.

 

After we'd fixed the timing we started noticing the car was missing every now and then. We re-checked the timing and valve clearances and took it out for a run and it started getting worse. We then put in new plugs, nothing happened, new leads, nothing, new dizzy cap, nothing, new coil, nothing, new condensor and points, nothing.

 

We checked the fuel lines and there was a blockage to the rear SU which we cleared out, but it just made the problem even worse.

 

It's now at the stage where the car doesn't have the power to climb a hill. We checked filters, pulled the carbies apart and checked their condition, put them back together and still nothing.

 

Pressure tests revealed:

 

Cylinder 1 : 120psi

Cylinder 2 : 130psi

Cylinder 3 : 160psi

Cylinder 4 : 160psi

Cylinder 5 : 150psi

Cylinder 6 : 150psi

 

Just some info about the engine, it's an F54 block with an N42 head, dished pistons, aftermarket mild cam, points dizzy.

 

Would the low compression in cylinders 1 and 2 be causing such a massive loss in power to the point it's not driveable?

 

The head is up for a valve grind in the next few days but any other ideas of what the problem could be would be much appreciated.

 

Other things to note are, when I block the intake of the front carby, it doesn't change the way the car idles, there's no suction from the front SU. The other thing to note is that the car deteriorated from a fully running car to undriveable in 2 days, what could possibly change it that quickly?

 

cheers, Zac

[Linton]

no, I dont think compresson is the problem, sounds like fuel, have you checked the fuel pressure at the pump

[luvemfast]

So there is no vacuum from the front 3 cylinders?

Is the carby seized? All working smooth?

May have a blown head gasket between 1 & 2 also.

 

[salty]

BULLZED, when you did the compression test, did you do a "wet" reading or "dry" reading?

rule of thumb, if any reading is below 10% of the highest reading it meens a rebuild

[bullzed]

So there is no vacuum from the front 3 cylinders?

Is the carby seized? All working smooth?

May have a blown head gasket between 1 & 2 also.

 

There is absolutely no intake through the front 3 cylinders at idle, carby isn't seized, pulled it apart today. Has a new head gasket, head was only put back on about 1 month ago after the last problem!!

 

Fuel pressure is fine, that's what is confusing us!

 

Salty, can you clarify what you mean by 'wet' or 'dry'?

[salty]

Salty, can you clarify what you mean by 'wet' or 'dry'?

with the engine as hot as you can get it, normal opperating temp is ok. all pugs removed, as is ,take a reading of all cylinders, then still with the engine hot, pump a small amount of engine oil into a cylinder then take a reading, do this to all cylinders, this is the"wet" part.

If the readings go up, this will indicate certain problems, usually worn/broken ring/s

[bullzed]

We'll have to do that. She doesn't smoke at all, no oil is getting past the rings or the valve guides. These were all checked when the head was taken off about a month ago. That's the reason we thought it was either fuel or electrical.

[salty]

some years ago I helped a guy who had trouble with a gemini, thing would idle, rev no problem but wouldnt drive, the engine would cut out or have no power to move the car.

turned out to be a wire connection at the distributer, wasnt making full contact, maybe look for someing like that but your compression readings are a worry

[bullzed]

The COMPLETE wiring on the engine has been replaced. It used to have the same problem you described on that Gemini. However now it doesn't even idle properly. Things have just gotten worse.

[salty]

another way to "find" a dud cylinder is to run the engine for a bit, then lightly feel the exhaust pipes at the head to see if one or more is running cool/cold

[salty]

the readings of one and two cylinders may indicate a crack/split in the head gasket between the 2 cylinders

also check the color of the plugs

[bullzed]

Thanks for all the suggestions Salty, I'll have a look tomorrow to see what's up. Getting a bit dark outside now.

[salty]

I have some other things you can do but I think theres enough there for now :'(

 

[Gordo]

I would be doing a spark plug read. See whats happening in side ,are the plugs all the same color, rich, lean, black brown white oily sooty, clean them and run for a short time and have another look. You should be able to see witch one's are working, It should tell you something. Good luck.

[luvemfast]

Why you running twin SU's in a 280?

(coming from the guy running triples in one)

[bullzed]

Never liked EFI. Just always enjoyed being able to play around with carbies. Triples will be on the cards soon enough.

[Zedman240®]

One thing I do highly recommend is replacing the points dizzy with an electronic one. That was the first thing I changed when I bought my first zed! It helps with many issues. Check also for leaks around the manifold with some WD40 etc...while the engine is idling, spray some around the manifold/head and if you hear the engine speed up a tad, it means its sucking in some of that WD40 and burning it in the engine like a extra splash of fuel. That should tell you there is a leak.

[luvemfast]

It's a 280 Dimitri, already has electronic dizzy.

[bullzed]

It's a 280 Dimitri, already has electronic dizzy.

 

Unfortunately it doesn't have an electronic dizzy, I said before it was a points setup. The motor is out of an MQ patrol. I'm currently completely broke and the electronic upgrade is just out of reach in the current time.

[luvemfast]

Sorry, my bad 

[MaygZ]

another way to "find" a dud cylinder is to run the engine for a bit, then lightly feel the exhaust pipes at the head to see if one or more is running cool/cold

 

And then attend your local hospital.  The skin may grow back, but your will never again feel the soft skin of a woman!

 

 

[Scottz]

Yeah,

and be careful spraying WD40 around a warm motor. It burns really good.

 

Fuel + Oxygen + Ignition = Power.

Ignition:You mentioned the power loss occurred after messing with the timing, so reverse the change and suss it from there. And check vacuum advance is not stuck.

Dizzy's on L series engines spin anti-clockwise instead of the usual clockwise like other 6's. L28 with SU's and points dizzy will run in the reverse firing order but a dog. Rotar spins in same direction but your leads are ass about. (Don't laugh - plenty of experienced guys have made the simple mistake).

 

Oxygen: Air leak entering downstream of carby.

Kink fuel line to carby1 and observe change. Do same to carby 2.

If blocking the fuel line dramatically changes firing then fuel is getting to the cylinders. If there is no or little change then air/fuel mix is not getting to the cylinders. Since you already checked fuel, then look for air leaks.

If you put your hand over carby 1 inlet throat and it does not suck your hand against the opening, then air is getting in somewhere else.

Carby piston is lifting freely? or jammed.

 

Fuel:

You already checked it - yeah!

Do you use mechanical pump? Or electrical?

Does fuel line go to carby 1 first or carby 2?

Bad pump pressure is usually only observed when reving. At idle a bad pump will still deliver enough fuel. Touch the throttle and it goes blahhhhh. Same for gummed up filter. At idle okay-ish. Give it a rev and blahhhh.

 

Exhaust blockage:

What sort of exhaust do you have. Any chance it is old and collapsed inside. Again don't laugh. This is one thing that has messed up a lot of mechanics and usually found after everything else is checked and double checked.

 

I thought you were getting rid of this car / engine ? Change of heart or just dogmatic?

Good luck.

 

[aegean]

Have you pulled the spark plug lead off each plug (one at a time) while it is running to see if there is any change ? I also had no power and removing the 3 rear plug leads made absolutely no difference to the running of the engine. Turned out to be a combination of the needle being corroded and the choke adjustment.

[bullzed]

Ignition and electrics are ALL checked over twice, all renewed and there is no shorting anywhere.

 

The one thing that I'm not so sure about is the 'wet and dry' test as I have dished pistons. If I were to put oil into the bore to try seal the edges of the piston during the compression test, I'd need a decent amount to get the oil to settle around the edge, but this would change the volume of the bore would it not? Therefore giving an inaccurate reading.

 

From what we can tell, the problem is the carbies. They were improperly balanced before, we fixed that but it still coughs and cuts out under load. The SU's we have are clones and they seem rather dodgy. The piston doesn't fit snuggly into the top of the SU and can rattle around despite fitting into a key-way. We used to have a 2 barrel + manifold from an MQ which we could have used to determine whether the SU's are working, however we sold it.

 

I'm not very up-to-date with SU's and wouldn't know how to tell this from that, is the piston meant to be running solely in a metal sleeve without a rubber ring?

[MaygZ]

Ignition and electrics are ALL checked over twice, all renewed and there is no shorting anywhere.

 

The one thing that I'm not so sure about is the 'wet and dry' test as I have dished pistons. If I were to put oil into the bore to try seal the edges of the piston during the compression test, I'd need a decent amount to get the oil to settle around the edge, but this would change the volume of the bore would it not? Therefore giving an inaccurate reading.

 

The reading doesn't matter.  It's the difference in the readings that matter.  If they all end up much closer in value, it indicates a ring failure in the cylinders that were already low.  If they all go up by about the same amount, it indicates a valve issue. 

 

Just give each cylinder a good squirt and give it a try.

 

I don't know, but someone here will, if all the L28's had steel valve seats ie are suitable for unleaded.  If not you may have burnt a valve??  Something to consider.