Misfiring Turbo engine

[Brandt]

My '83 Turbo have been missing since the day I bought it.

I've done all the regular things, such as rebuild the cards, and replaced the spark plugs and leads. The rotor and cap as well as coil looks new, quess those are things the previous owner replaced.

(One thing I discovered after purchasing the car was that it has a NA head on, but with the Turbo CAMs. I will replace the head sometime in the future, when I have more time/sapce available.)

The missing is evident at idle, and it goes right through the rev range.

Today I was checking if the coil was regularly being fired by the ignition system on a scope, but that looked OK. I noticed that when I rev the engine to 3000rpm, is that the "turbo air intake hose" swelled (puffed) briefly at times (say once every three second). Surely there must be sone sort of backfire through the carburettors for this to be happening. I'm scared to think what this must to to the turbo under boost!

What woulb be the cause of a backfire through the carburettors? Please help!

Edited February 19, 2008 by USAndretti42
Made topic title clearer

[Brandt]

Buddsy, yes, I'm quite sure it is the NA head. I haven't measured the valve stems, but it has the NA inlet manifold, with associated water pluming (and the plumbing did not fit the description of the USA turbo version either). It even have 2 thermostats in (one on the water pump, and the other the turbo inline Y themostat)

Can anyone explain the reasons for cumbustion in the inlet manifold, or maybe point me towards some literature on the subject?

[Brandt]

Buddsy

Tell me more about the anti-reversion plates. Where are they situated and what do they look like?

Brandt

[dazmans3]

Hi

Have you done a compression test,(Start with no 4, its the more likely one to go) Mine was missing, turned out the cyl head gasket was on its way. have you checked the engine breather & dip stick for dark cream like substance.

Are you in the US? or do you have a US spec car?

Don't know if your 83 car would warrent this, but HC turbos also have a smaller inlet manifold with 45 carbs fitted & the thermostate on top of the water pump. I would check you don't have a themostate fitted in here aswell, as you do not need two, surely this would hinder warming up, & the water flow. Would be interesting to see how it has been plumbed in.

Any chance of some photos?

Daz

[Brandt]

Hi Daz.

I will have a DOM version, as I am in South Africa, and us being ex-British property, we would get the same model as the standard in the UK. In the chassis number also match up to that.

I haven't done the compression test, but it seems I will have to on the weekend. Interesting you mentioning cylinder 4, because whilst overhauling the carbs, I noticed that the air path from the turbo pipe into the carb for cylinder 4 was quite black. If I had a sticky inlet value on cylinder 4, could that explain the backfire into the carb?

As for the head gasket: I noticed that air keeps on collecting the radiator, which is apparently another sign of a problematic headgasket...

I have installed a 77

[dazmans3]

hi Brandt

No 4 & No 3 are common on the LC's, can't realy say for the HC's as yet, but I ve heard of more HCs making higher miles before major work is required. I believe It's due to the poor cooling flow for the hight temps generated by the turbos.

If I recall I was getting additional air in my rad aswell

I did away with my external Therm when I converted mine to HC, seams to run a lot better, ie warms up more quickley, much better heat from the heater. I was able to easily adapt as I had the Lotus cooling mod(which has been recently covered on here) this was added to later S3s by Lotus poss under warrenty. yours being an 83 then you may not have fitted, but if you have an expansion tank fitted to the Right side(same side as Battery) will indicate you have.

Daz

[USAndretti42]

Certainly a sticking inlet valve could lead to backfiring through the inlet. It could also lead to the valve head falling off the stem as the valve hits whatever is keeping it open at higher speed than it should. If that something is under the head of the valve and to one side, it could twist the head off or fatigue it off.

Lean mixtures can lead to spitting back through the carburetors.

Have you tried running the car at idle with the turbo disconected from the carburetors to see what happens?

[Brandt]

Hi Everyone

I hit a snag bleeding the clutch (mainly stupidity) but that is now sorted, so I'm back to the engine.

Daz, I did the compresion test and measured an actual zero on cylinder 4.

With the symptons as they are, I'm sure its a very stickey valve. Since it is the wrong head (NA), I will change it for a turbo head. Anyone have a good conditon turbo head for sale?

Then the piping for the NA head:

I have added the Transparent bits so you can see where the pipes run when they are hidden. The green pipe goes to the thermostat housing. There is no thick water pipe outlet on the extreme left of the head, at cylinder 4. I believe the blue pipe goes to the interior heater. The Yellow pipe seem to be an addition, where a pipe was tapped into the inlet manifold, to supply the thin pipe on the original turbo aluminium banana pipe. Why they simply didn't blank off the thin pipe on the aluminium banana pipe I don't know.

Something important, is that the normal takeoff point for the internal heater (for S3 heads) have never been drilled on this head. (It should have been on the extreme right in the top picture) I suspect this means that this head belonged to an S4. Is this true?

Daz, can you post here(or email to me) a picture(s) of you modification, I haven't been able to find it on the forum.

Here is a picture of a S3 turbo head that I have been able to source:

There seem to be two studs missing on the inlet manifold, and only 4 studs to keep the cam housing in place. Is the cam cariers held in place only by studs; or also by bolts?

Brandt

[910Esprit]

OK - Its an LC head identified by large water pipe.

The 'missing studs' are in fact correct - but I agree the design looks a bit shabby!

The 4 studs for the cam carriers are correct, the remaining fixings are male headed torx bolts - wait for it.... priced at 9.99 each from Lotus!!!

Are you going to reuse the NA inlet manifold? - The Turbo manifold is worth upto 15 BHP on a NA car (as reported to me by one of the best tuners of the 907....). So I assume the NA manifold will also have some negative impact on a turbo car (including more lag?)

cheers Steve 84 turbo

Edited March 5, 2008 by 910Esprit

[Brandt]

Thanks for the info on the inlet manifold, Steve. I have a turbo inlet manifold and will be using that one then when rebuilding!

One more question. On the Turbo inlet manifold there are two black pipes. The one black pipe is for the water cooling system. What is the other black pipe for?

Brandt

[910Esprit]

Does this help?

I have just reread your last post and think I now understand!

The thicker pipe is for coolant

The thinner pipe is the vacuum pipe for servo & heater controls

cheers

PS when are you removing the old head, I'm intrigued what the problem is - I wonder if its related to using non-turbo exhaust valves?

Edited March 5, 2008 by 910Esprit

[dazmans3]

Hi

Oh dear! '0' on no 4, not so good. Something def wrong there.

Ok, I have attached photo of the diagram I drew for the LC S3 Turbo Cooling Mod, fitted with AC. This was fitted from about 86/87 on wards. It's a bit crude, as I had to draw it out my self, but you should get a good idea of how the pipes should be routed.

Do you have a parts manual, as there is a list of parts for this cooling mod in there, just no diagram. The numbers on this diagrm correspond to the ones in the parts book.

There is a proper Lotus diagram for this. I got it from somewhere on this forum from someone who very kindly made it available onhere. I did print it out, so If I cant find it on here or my PC, I will dig out the hard copy, take a photo of it & send to you.

That is an LC Turbo head you have there isn't it? Did you not consider going for an HC Turbo Head. It has better coolant ducts round the head. It is one of the reasons I went for the HC engine in mine.

Daz

Edited March 5, 2008 by dazmans3

[Brandt]

Steve, I'm also quite interested to know exactly what the problem is, as I suspect the inlet valves. The pervious owner (who hadn't realise it was an NA head) replaced the piston rings. I don't know if the little added compression of the new rings pushed the top over the limit.

Daz, thank you very much for the detailed picture. I do have a manual with the picture, and from what I can remember, your diagram is definitely different from my manual. Unfortunately I had completely misunderstood you earlier. I thought you had fitted the NA water pump (with integral thermostat) to your car.

Well, I've started to source the parts, but this is going to be a slow project, as I'm first going to do some additions at home (I'm putting up some carports for the "fleet" so I can work on cars in the garage!) I'm also studying Bigsi's thread to learn what needs to be done. I'm still very divided over whether doing it myself or taking it to a garage. But, it

[markt]

Hi Brandt

Where in SA are you based? - For the big jobs, and to make sure things are done properly, I can recommend an excellent mechanic in Laser Park, Honeydew, Johannesburg if it helps?

Cheers - Mark

[dazmans3]

Daz, thank you very much for the detailed picture. I do have a manual with the picture, and from what I can remember, your diagram is definitely different from my manual. Unfortunately I had completely misunderstood you earlier. I thought you had fitted the NA water pump (with integral thermostat) to your car.

Your Welcome.

Yes I decided to fit an HC engine instead of rebuild my LC engine, From what I ve recently found out about it, it seam not to have had a very long life between rebuilds. The HC engine has the water pump with integral Termostate.

I have found & attached the details about the Lotus Cooling Mod, if you can't upload it for what ever reason, then PM me your email & I will send it that way.

Daz

S3_Turbo_cooling_mod.pdf

[Brandt]

Hi Mark

I'm in Capetown, but for a job like this it may be worth to send the car to Jo'burg. So Mark, please send me the contact info.

And thanks for the pdf, Daz.

Brandt

[markt]

Hi Brandt

Sent you PM - Hope it helps.

Cheers - Mark

[LOTUS]

Thats a nice clean engine you have there. They dont stay that way for long if you do the unthinkable and actually drive the car about! I get depressed when I look at the nice shiny parts I have bolted on to the car 2 weeks previously, now covered in a layer of salt/rust/oxidation

Joolz

[Brandt]

Hi Everyone

Finally the head is off. One exhaust valve is somewhat damaged for cylinder 4. See picture. Its not in focus, but gives a good idea. If you look carefully you can see the valve seat in places!

I've also checked; the exhaust valve stems are 7mm (not 8mm), and there is no big water outlet on the front of the head, so this is definitely a NA head. But I've got a Turbo head to put in, so I'm all set.

I think the pistons looks OK. The previous owner said he had replaced the rings. I'm seeing much fine horisontal scoure marks on the cylinders surface (I assume due to honing), but very few vertical scour marks. Am I correct is saying that it means the rings have not yet bedded in?

(And I'm proud to say, with an engine crane it was a one man job to lift out the engine with gearbox intact!)

Regards

Brandt

[910Esprit]

Well done.. I suspect you will be very pleasantly suprised when you have compression of 4 cyls. The car will feel a lot more than 25% more powerful.

Your bores sound ideal. You dont want to see any vertical scoring at all. Light crosshatching is good and usually evident for many thousands of miles, it does not indicate that the engine is not run-in.

Steve

[Brandt]

Thanks for the encouraging words Steve. I'm still surprised how smooth the engine ran, even with the misfire. So I'm sure the power increase will be very noticible!

I actually expected a inlet valve to be sick, as the inlet manifold/carburttor insides was quite black. Can anyone explain to me why the inlet side should be black? I was wondering if the gasses inside the cylinder sometimes ignited on the suck stroke (inlet valve open), as air could enter forn the inlet and exhaust manifold during this time,

Regards

Brandt

[USAndretti42]

When the engine is running at part-throttle and the inlet manifold is under a vacuum, exhaust gas left in the cylinder can be drawn up into the inlet manifold causing said blackness.

[Brandt]

Hi Everyone

Wel the Lotus is all assembled again, but it still has the misfire . I can clearly see the backfire through the carbs at this time. And all the cylinders are spitting.

So I took the Lotus to have it dyno tuned. Unfortunately the dyno guys I went to are not too experienced on carbs, so they could not help, but they said the Esprit was running very lean, all the way to 4500RPM, at which time it switched to becoming very rich. So rich they said it was just about flooding! And they said it was running so lean at low RPM, that melting pistons is a possiblility.

All the jets are as specified by the manual, well so I thought.

When I got the car back home I rechecked all the jets, and found that the needle jet was a 150 (on both carbs), instead of a 200 as specified. All the other jest are the correct size. I took the carbs apart and checked that everything is clean and no piping is blocked. This all looked good.

Can the too small needle jet explain why the engine is running lean at low RPM? I would have thought that with a too small needle jet it would run fine at lower RPM and go lean at high RPM.

Any ideas?

Can ignition timing have any effect here?

Kind regards

Brandt

[molemot]

Check the true diameter of the slow running jets. They can block up with varnish from evaporated petrol..then you have your lean mixture up to the point where the main jets kick in. I had just such a misfire and finally cured it by cleaning out the slow running jets with a piece of calibrated guitar string, of exactly the correct o.d. as the jets intended i.d. Before that,I'd tried everything, ignition, timing, carburetter adjustment, balancing, the works. After, it all came together, balancing was simple and all the misfiring had gone..it had misfired between 3000 and 4000rpm..just where you sit at legal motorway cruise, which was an infernal nuisance...but the misfire did clear if you gave it a bootful of throttle/accelerator pump/main jet. Definitely worth a check..if it's the same as mine, you cannot clear the jets by compressed air blast or any of the solvents I tried. Needed to be physically cleaned out.

Spitting back through the carbs. is definitely a sign of weak mixture..given that the ignition timing is not overly advanced. The needle jets probably won't affect the slow running, if they are too small then you might get too little fuel in the float chamber to sustain high RPM.

Edited March 31, 2009 by molemot

[910Esprit]

Brandt

I dont think the needle jets will be your problem, although its probably better to have them stock.

There is only one carb adjustment for the lower revs range - The mixture screws. I assume you, or your dyno man have tried adjusting these (anti clockwise to enrich)? As you say, spitting back through the carbs suggests you are running weak. Do you know you idle CO2? The book suggests around 1% - but I need more like 2.5-3% to get it pulling nicely.

Apart from the 'gummy' jet theory suggested by John, its probably also worth checking float height, fuel pressure, the fuel regulator, although none of these would really explain why there is no fuel starvation at high revs.