TB42 running on 4 cylinders?

[4 by 4]

Hey guys having some problems with my tb42 at the moment. It seems cyl 1 and 2 are either not firing properly or completely out of time as when I pull the leads off the engine idle doesnt change at all. I've replaced leads and plugs, it already has a gt40r coil and a pirahna elect ignition and extended rotor button, set timing to about 14 but if cyl 1 isnt firing right I would assume this would completely fk up the timing? I have also checked and re-gapped the tappets the other night (they were out a bit but nothing extreme) and also cranked the engine over too make sure there wasnt any valves sticking. While checking the tappets I noticed a little bit (not alot at all) of coolant in the rocker cover which lead me to assume head gasket/head. So just now before writing this, I checked the compression of all cylinders and the results were 135-145, so not alot of difference. Also I have leaned the auto choke off as much as I could and have removed the noise suppressor. The strange thing though is when cold the idle is shit house (assuming because of the auto choke but whatever) and when warm it idles pretty nicely. When driving it until about 2500 rpm it runs like crap but after that it pulls like a train, almost like its running on 6 then.

I am completely lost as what to do right now so any suggestions would be great, I'll start with the simple things simply because no one wants to spend money where it is not needed :clapping:

Cheers

[Parksy]

I'd be leaning towards fuel delivery issues first in my opinion. Check for vacuum leaks by spraying some wd40 on and around gasket seams and joints and see if you get a change in rpm. When was the carby last rebuilt? Over time gaskets and seals will dry out and not seal properly.

The coolant found in the rocker cover is concerning and should be addressed ASAP.

[4 by 4]

I'd be leaning towards fuel delivery issues first in my opinion. Check for vacuum leaks by spraying some wd40 on and around gasket seams and joints and see if you get a change in rpm. When was the carby last rebuilt? Over time gaskets and seals will dry out and not seal properly.
The coolant found in the rocker cover is concerning and should be addressed ASAP.

I've checked for vaccum leaks the other day and couldn't find anything. Spoke to a mates dad who is pretty cluey on engines and he suggested that maybe the intake manifold is leaking @ cyl 1+2 so i've tested that the best I could by taking the carby off and blocking it the best I could then pumped air into it and listened for leaks but couldn't find anything. I also sprayed heaps of wd40 on the intake also and didnt notice anything suss.

If it was fuel delivery though, how would it only be affecting cyl 1+2 so badly though? I wouldn't have a clue when carby was rebuilt unfortunately.

What would coolant in the rocker cover be though? I assumed head so comp tested it and everything came back as 135-145 and we then tested it again with the throttle fully open and everything was at 150 (give or take 1-2) Head was also replaced 3 yrs ago by previous owner.

[Parksy]

Why are you saying there's coolant in the rocker cover? Is there signs of milky oil? How does the engine run when you disconnect say number 6 or 5 ignition lead(anything but 1 or 2)?
Trying to get to the bottom of these issues is a pain and can take ages, took me about 3 months to get to the bottom of my rough running tb42e, which turned out to be an intake gasket that had dried up and didn't seal properly anymore.

[4 by 4]

Why are you saying there's coolant in the rocker cover? Is there signs of milky oil? How does the engine run when you disconnect say number 6 or 5 ignition lead(anything but 1 or 2)?
Trying to get to the bottom of these issues is a pain and can take ages, took me about 3 months to get to the bottom of my rough running tb42e, which turned out to be an intake gasket that had dried up and didn't seal properly anymore.

I saw small traces of coolant in their when doing tappets, but only the tiniest bit. Im pretty sure the oil isnt milky as I dropped about 2L's the other night to check that, but I will be doing a full oil and filter change either tomorrow or tuesday. When I take leads off anything but 1+2 the whole engine revs drop like it should and almost sounds like its going to stall.

Also just tried my brothers dizzy cap on mine which made no difference.

Yeh I've only been going at it about a week trying to source the problem as I bought the car knowing it had a misfire, assuming it would be a simple fix but turns out it's not :/

[Parksy]

Have you held number 1 or 2 leads against a good earth while running to see if you're getting a spark to the end of those leads? If you had a timing light you could make sure that number 1 was firing correctly.

[mudnut]

If the car has only done many short trips, and not really had time to warm up properly, condensation can form under the rocker cover.

[4 by 4]

Have you held number 1 or 2 leads against a good earth while running to see if you're getting a spark to the end of those leads? If you had a timing light you could make sure that number 1 was firing correctly.

Yep, good spark from 1 + 2. Have also rotated plugs and leads around to rule those out. I have a timing light, does just setting the timing prove its firing/sparking at the correct time?


If the car has only done many short trips, and not really had time to warm up properly, condensation can form under the rocker cover.

That seems highly likely, so hopefully that's all it is

[Parksy]

Yep it should. Should be set at 10 degrees before top dead center. It sounds like most avenues have been exhausted and I'm leaning towards replacing intake gaskets, vacuum hoses and things like that. Not an easy one to solve unfortunately.

[4 by 4]

Yep it should. Should be set at 10 degrees before top dead center. It sounds like most avenues have been exhausted and I'm leaning towards replacing intake gaskets, vacuum hoses and things like that. Not an easy one to solve unfortunately.
When I bought the car it was running about 25 advance which amazed me.. so I have backed it off to 14 at the moment but I will double check it tomorrow. It didn't seem to make a lot of difference either.

I might order a new coil and ignition tomorrow as it has the gt40r so it only runs 9v I believe, and the piranha ignition in it at the moment looks like it has seen better days.

Frustrating stuff..

[4 by 4]

Bit of an update.. Ran 12v straight from the battery to the coil and bypassed the resistor and then checked all the leads/plugs were firing. Found that while on 12v cyl 2 was firing, however when removing the lead the change in engine rpm isnt quite as noticeable as 3/4/5/6. It ONLY did this on petrol. So I'm just taking a guess here but, leaking intake manifold somewhere around 1+2? Because gas is more pressurized than petrol it would be able to leak out easier, meaning that the cyls would still be getting fuel, just no where near as much?

[taslucas]

When I bought the car it was running about 25 advance which amazed me.. so I have backed it off to 14 at the moment but I will double check it tomorrow. It didn't seem to make a lot of difference either.



25 degrees advanced would be for the gas. Gas needs it more advanced than petrol. Putting back to 14 degrees may have a negative effect when running on gas.

[4 by 4]

25 degrees advanced would be for the gas. Gas needs it more advanced than petrol. Putting back to 14 degrees may have a negative effect when running on gas.

He said it was tuned more so for gas but even on 25 advance it ran not too bad on petrol.

[taslucas]

He said it was tuned more so for gas but even on 25 advance it ran not too bad on petrol.

Yes but putting it back to 14 advanced probably run that well on gas.

[Parksy]

Bit of an update.. Ran 12v straight from the battery to the coil and bypassed the resistor and then checked all the leads/plugs were firing. Found that while on 12v cyl 2 was firing, however when removing the lead the change in engine rpm isnt quite as noticeable as 3/4/5/6. It ONLY did this on petrol. So I'm just taking a guess here but, leaking intake manifold somewhere around 1+2? Because gas is more pressurized than petrol it would be able to leak out easier, meaning that the cyls would still be getting fuel, just no where near as much?

Replace the intake gasket, use some spray on sealant just to be sure. Might be a pain for a few hours(by doing it I mean) but then it might solve your issue and if not, it's one thing eliminated. Gasket replacement is a cheap fix if you do it yourself.

[4 by 4]

Replace the intake gasket, use some spray on sealant just to be sure. Might be a pain for a few hours(by doing it I mean) but then it might solve your issue and if not, it's one thing eliminated. Gasket replacement is a cheap fix if you do it yourself.
I'll look at doing that probably this weekend. Is there a way to leak test the manifold while it is off?

[davo94]

Really not needed. Just hang the manifold to the side rather than removing if from the car. Its guicker.

[4 by 4]

Found my problem tonight! Was a leaking intake manifold gasket around cyl 1 and the thermostat housing, but it was only leaking on the underside which took alot of messing around to find (even after 3 attempts to find vac leaks in the previous days) Gasket was pretty well rooted and was crumbling away, which is strange because it looked very old but the head was replaced in 2010, I would have thought they would have done the intake at the same time but oh well. Decided to take entire manifold off which was a PITA but since I knew it wasnt going to be finished tonight I'd rather have it off and block off the intake holes to the motor than leave a manifold dangling in the engine bay.

Thanks for the help everyone especially Parksy

Quick question also, should I fork out the 60 or so dollars for a new gasket or would gasket maker be better/just as good? Im happy to pay the money for a gasket if its the better option

[Robo]

Gasket with some ,hylomer seleant on it.
Hylomer will help to prolong the gaskets life.
Also forms a better seal at the same time.
Not cheap $20+ but small can goes a fair way.

[Parksy]

Happy days, glad you've found the problem. If you still have the manifold off now is a good time to check you don't have a leaking oil cooler/blanking plate (which ever is fitted). Doesn't use a gasket, just silicone, but a pain in the backside to change if the manifold is fitted. Located between the starter motor and the intake on the block.

[4 by 4]

All I can say is WOW, what a PITA job. The old gasket was glued to both surfaces and it took me and my brother a solid 2-3 hrs just to remove the old gasket. Almost finished everything, few small things to do tomorrow then we shall see if its done right! :D

[GQ TANK]

Great news - otherwise you would have been looking at a problem with the head