Sierra 2.0 DOHC accelrating itself to destruction.

[philibusmo]

I bought a Sierra last Saturday, a 2.0 DOHC GLX with a carb and seemingly in excellent condition. 10 months MOT, 5 months tax, 1 elderly owner and a mint interior, all for £621. Bargain I thought.
I drove it home and it was smooth and quiet with no issues what so ever, then I took it out to drive into town and put my foot down a bit, the second choke opened and it took off, then when I took my foot off the accelerator, it didn't stop accelerating and I had to slam the brake on to get it to slow down, I pushed my foot under the accelerator pedal and it was fully up but the car just kept accelerating so I pushed the clutch down and it started bouncing off the 7000RPM limiter. After slowing down and blipping the accelerator a couple of times, I drove it home to find the issue, the little plastic thread that holds the accelerator cable had snapped and I assumed the cable had become caught, I did a quick bodge on this and took it out and it felt fine again, until I blatted up a hill where the second choke opened and it happened again, I slammed it into 5th and what I thought was smoke billowed from the back of the car. I then blipped the throttle again and the car was driving fine but the smoke kept billowing. I got it home again. The Sierra then wouldn't start when I had stopped the engine, until about half an hour later when it started again and drove down the drive just fine.
I then fixed the cable and took it out again, and once again it all seemed fine, until the second choke opened and then there was a complete repeat of events. Acceleration, high RPM gear change, smoke but then blip the throttle and running fine. Once again I got it home, slowly and went under the bonnet to find that the smoke was actually steam and coming from the back of the engine (seemingly from both sides) there is also now no water in the rad over flow and once again would not start for about half an hour after the incident, but then runnign fine again. I guess that the head gasket has gone, so I will replace that asap, but with the acceleration problem, I am stumped. Any of you guys have any ideas?
Also is there anything other than the head gasket it could be, am I likely to have broken anything else? I have also bodged the accelerator cable and when stationary all seems to be working properly and smoothly.
Still 4 hours from buying a perfectly working car to having an undrivable one must be some sort of record without a crash.

[elmotheewokking]

Sounds like there's something in the carb causing it to stick open. I'd whip it off and clean it up.
As for the steam, compression test should tell you if the head gasket has gone, or test for leaks.
Thought the HG had gone on my sisters KA once when she came home with steam pouring out of the bonnet. Turned out the thermostat housing gasket had gone and it was squirting coolant straight onto the exhaust manifold. Easy fix.
Good luck!

[scaryoldcortina]

Elderly owner probably never used the second choke, so I'd suspect a sticky flap or linkage. The steam might be HG or it might be something simple - all the violent revving/braking etc might have split one of the heater hoses at the back of the block.

[chairchild]

Could be carb icing? Had it a total of three times driving my old scim home after buying it. Bloody scary when you've never had it before!

[bortaf]

Carb icing will make the car hesitate not rev it tits off ?

[philibusmo]

It's not carb icing, the day was reasonably warm so I very much doubt that was the problem. Also checked all the hoses and they all seem in great condition. Will have a look at the second choke, see if it is sticking but it all seems good when stationary, no spots where it appears to stick, but maybe it is ever so slight and the airflow is keeping it open?

[dodgerover]

Carb icing is when the flow of air/fuel through the carb is enough to cause it to get cold enough to freeze up, outside temperature doesn't really matter

[philibusmo]

Would it cause it to ice open and not shut though?

[philibusmo]

Also it has the full restrictive air filter housing o it pulling air from near the exhaust.

[scaryoldcortina]

I'd say icing is unlikely. For one thing, it's usually only a problem on extended runs at high throttle, and second if the car is standard it has several design measures to prevent icing.

I'm still saying it's a sticky secondary throttle flap. It's vacuum operated on a 2E2 pierberg, so once it's open there is only the return spring to bring it back.....

[bortaf]

It's a weber on the DOHC, a 2v tld but still has a vacume secondary, i'd be checking the linkage as above then the throtlle kicker and low vacume enrichment device for a split in the diaphrams, there's 4 diaphrams on those carbs but those 2 are the likely ones IME

[philibusmo]

Small update on this. Drove it this morning for about 1 mile and once again all driving perfectly. However as I was pulling into the drive it stalled (not sure if it was me or the car) and then wouldn't start. It got pushed up the drive with steam coming from under the bonnet again, except this time it left a small trail of oil spots. I tried refilling the rad overflow and found the water to be pouring out the back of the engine, with some investigation it has turned out that a core plug has popped from the back of the head. Very strange. The only reason that I can think of is that the head gasket went at 7000+rpm and then the pressure create in the cylinder went into the water ways and put about 100psi behind tr core plug, popping it. Does that seem likely, or could it be something much worse? Also the oil on the ground, the area behind the core plug is very oily and grimy, could it be very hot water cleaning the oil from that area as it is pouring from the missing core plug or am I being a bit too optermistic there?

[bortaf]

IME if you have a twink withOUT a leaking cam cover your a lucky man, usually oil washed off by hot water leaking is ready mixed and rainbow like fresh only oil is black and blotchy (that may not make sense lol )
TBH it would take a servierly warped head to pop a core plug cos of overheating and warping but it depends on how long you've run it without water ? TBH i wouldn't have been driving it with the water leak seeing how bad these engines are for HG failier and the fact it's an alloy head on an iron block (the worst combo for warping a head IME)

[philibusmo]

I think the core plug threw itself out the first time that all the steam first made itself apparent. i think all the water has been making its way out since as it really hasn't gone very far (4-5 miles maybe) and all in very short journeys. Still runs perfectly when cold, but it won't be going anywhere now until this problem is fixed. So are we saying that oily gunk = rainbows and nice oil = splodges? All I saw was rainbow oil but the ground was damp.

[bortaf]

Damp ground will mask it but a decent leak (wronge use of the word there but i hope you follow me) lol would leave an oil splodge that is raised off the surface whereas oil ready mixed will be thinner, it's a hard one to explain sorry you need to experiance it to understand and i am curse word at explaining it lol

[philibusmo]

Ok well in that case I will go with ready mixed, but there is no emulsion on the dip stick or in the oil filler. Well it is getting a new head gasket anyway as the head has to come off to put the new core plug in, but I can't find a timing chain tensioner anywhere, just the full timing chain set for £expensive. I already have the gasket set, just need to buy the bolts and plug, which I have found but can't seem to get hold of the tensioner. Tried various Internet sites, eBay, and even my local ford dealership, but they are consistently useless so might have just gotten all confused with their computer. Next to try the local motor factors.

[scaryoldcortina]

The tensioner can be re-used.... To reset it, you pull the centre out and move the two circlips to the bottom two grooves and then push it back in. It should go all the way to the bottom then pop up a little and lock. Fit it to the engine, put the arm with the toothed wheel over the top and on the chain, then tap the top of the tensioner with a hammer/screwdriver and it should pop out and hold the arm up against the chain.

[rodney]

at the point the thing revs its nuts off , turn the key off!!,.

[nomad]

As above, I'd vote for a sticky 2nd choke as the previous owner was a sensible type

Dec 24, 2011 20:43:48 GMT rodney said:

at the point the thing revs its nuts off , turn the key off!!,.

+1 - but don't take the key out or the steering lock will jam the steering

[rodney]

as long as key stays in it wont lock steering , ive had a steering lock come on when driving before and it is scary ;D