V8 running extremely rough after cleaning intake with carby cleaner

**stuee** · 12th October 2010, 10:46 PM

Hi all,

Stuck at the in-laws house atm with the disco as its unable to drive under its own steam atm.

Symptoms are:
- Missing and running erratically (like only running on 3-4 cylinders)
- Occasional sharp knocking sound coming from heads
- Will not accelerate

These showed up on the way here but a good rev of the engine under load cleared it up and it was fine (I should have turned back home then...). After sitting over dinner it’s now worse than before and wont accelerate.

The only thing I can think that would be causing the issue is me cleaning out around the throttle body with a good dose of carby cleaner as up until now its been running great and these problems came up all of a sudden. I'm thinking the carby cleaner has perhaps removed some of the lubricating oil around the valves causing them to stick resulting in the sharp knocking sound (definitely metallic)???

Ignition checks out fine and to double check I replaced the rotor with a spare but absolutely no change. The only other thing I can think of is fuel supply but I cant see that resulting in the knocking sound. Either that or somehthing has changed the timing completely but I cant see how that would have happened.

Any help greatly appreciated.

Cheers,
Stuart

PS I've ben searching like crazy and so far cant find any threads that match my symptoms or mention carby cleaner causing these sorts of problems but Im more than happy to read through any suggested threads.

Edit* Looking at the valves throgh the oil fill hole it looks very dry. I've never really paid much attention to this before but I would have thought it would have a nice oily film over everything. Perhaps I've got an oiling issue, either way I'm ot getting out of here anytime soon I dont think

Edit 2* - Called it quits. Going to get it towed by RAC tomorrow. Dont want to damage the motor

Edit 3* - Not discounting ignition or fuel now I've thought about it more. I was recently trying to diagnose my poor fuel consumption and was testing for a faulty vacuum advance module. Its possible I stuffed something up doing that. With the fuel I just filled up on the drive beofre taking my car out tonight, possibly a bad batch of fuel... And of course this comes not even a week after dropping a heap of money on new discs, pads, bearings, wheels and tyres

**PhilipA** · 13th October 2010, 08:30 AM

Stuee,
IMHO you have to review what you disturbed to find the problem.
Carby cleaner cannot do anything to the valves . The rocker gear always looks dry but it is fine.
If I were you , I would look at the plug wires and check that they match the firing order.
Unless you used Sooo much carby cleaner that you flooded the engine. In that case pull out the plugs and turn it over without plugs after removing the fuel pump relay. To start, place the accelerator flat to the floor and crank.
Regards Philip A

**bee utey** · 13th October 2010, 08:42 AM

Sounds like moisture in the dissy cap. Remove the cap and look for finely beaded water inside. A hair dryer is best to remove it. Or leave the cap off during a sunny hour or so, that is if you have any sunshine available up your way at the moment.
Then look at the plugs, are they fouled? maybe bring along a new set to fit.

**stuee** · 13th October 2010, 09:51 AM

I was going to have the car towed to my local LR workshop but I think I may head up this afternoon and delay it for a day (Its in a reasonably safe cul-de-sac on the street). I was trying to test the vacuum advance module and all I was really doing was sucking and blowing on the vacuum advance tube and trying to stick it to my tongue

. I possibly gave the distributor a hard knock but no more than when I'm usually fart arsing about in the engine bay.

The only other thing I can think of in that regard is that I've jammed something in the vacuum advance module that has stuffed up the ignition timing enough to not let the car run smoothly.

I'll take the distributor cap off in the daylight and inspect it for moisture though, couldn't see crap last night.

I didn't check the plugs last night but I guess it could be possibly the crap that dislodged in the intake has fouled them up quite bad. I did check the plugs prior to cleaning out the intake manifold with carby cleaner though and they appeared ok.

I will also try clearing the engine with the spark plugs out in case it is flooded.

The engine seems to start fine but as soon as it comes down from that initial 1100rpm or so that it goes to it coughs and splutters (basically about 2 seconds after start-up).

Cheers for the suggestions guys.

**Chops** · 13th October 2010, 10:58 AM

Gday Stuart, I had similar problems with mine, a 96 V8, when the fuel pump went on it,, started fine, then went to pieces almost straight away. Mine ran quite roughly untill i filled it enough to get the level above the broken section of pick-up tube. I had to have mine virtually full to be able to drive it,,
Also, you mention you'd not long filled up prior to this,, it could be a load of bad fuel, and this wouldn't help you either, and might add to the knocking noise maybe.
Other than that, it sounds electrical-ish, like the timings been moved substantually,,,
Good luck with it dude,,

**stuee** · 13th October 2010, 11:32 AM

Originally Posted by Chops

Gday Stuart, I had similar problems with mine, a 96 V8, when the fuel pump went on it,, started fine, then went to pieces almost straight away. Mine ran quite roughly untill i filled it enough to get the level above the broken section of pick-up tube. I had to have mine virtually full to be able to drive it,,
Also, you mention you'd not long filled up prior to this,, it could be a load of bad fuel, and this wouldn't help you either, and might add to the knocking noise maybe.
Other than that, it sounds electrical-ish, like the timings been moved substantually,,,
Good luck with it dude,,

I filled up only 25km or so before the issue came about so its still pretty much a full tank so hopefully its not the fuel pump not picking up fuel (that was only replaced 18 months ago). Not ruling out bad fuel atm but it would have to be really bad as when I topped up I only put 20 litres in.

**agrojnr** · 13th October 2010, 01:29 PM

I would check the pick up pipe on the fuel pump to see weather the pipe has a blockage of dirt or even a pebble Ive seen it happen on a paj

Adam

mike 90 RR · 13th October 2010, 05:33 PM

Originally Posted by stuee

I did check the plugs prior to cleaning out the intake manifold with carby cleaner though and they appeared ok.

I've got $2 riding on .... that you have reversed some of the spark plug leads

Cheers
Mike

**stage one** · 13th October 2010, 09:35 PM

When my 8v did something like that it was the 8 week old "top gun" High tension lead from the coil to the dizzy. Had a resistance of 11+, should be about 3.5 omes per foot. I thought it was a fuel problem to.

**stuee** · 13th October 2010, 10:29 PM

So the best piece of advice:

Originally Posted by PhilipA

Stuee,
IMHO you have to review what you disturbed to find the problem.

The problem was self induced MAF destruction...

I tested the MAF Tuesday after work (prior to going to the inlaws) and all checked out sweet. Voltages where they should be, everything seemed micky mouse, except that I was too lazy to seal back up the top of it after opening it to resolder the adjustment screw to the POT (its been open for ages now). Seeing as it was not sealed tight a bit of water had made it into the MAF body while washing the einge bay out from the weekends exploits, all still was working fine so I dried it out and noticed there was some oxidisation occurring on the exposed parts of the circuit board. No problems I think, I'll give it a good spray with the circuit board lacquer I have inside. So it wasn't me dicking about inside the MAF with a soldering iron, wasn't me getting water in the thing after washing the engine bay out, it was me trying to carry out some preventative maintenance with the circuit board lacquer.

My theory is that as the MAF heated up some of the lacquer must have flowed onto the hot wires. When I was on the way to the inlaws the big rev was probably enough to clear the still liquid lacquer from the hotwires, allowing them to function again. Parked up over dinner its probably flowed back onto and set on the hot wires so that when I've gone to start it again the engine thinks there is no air going to the engine so its not giving it any fuel.

Of course I only found this after pulling all the spark plugs and turn over the motor to clear a possible flooded engine, triple checking the order of the HT leads, removing the faulty vacuum advance actuator and fire it up again all for no change then notice I hadn't put the locking pin back on the MAF connector after all this so gave it a yank to see what would happen and presto, the engine started idling reasonably (for no MAF) and revved freely.

So, what have we learned from all this? Nothing. I'm just a bit of an idiot

I've actually stumbled across some really good threads regarding my vacuum advance issue while trying to solve this so not all a waste of time.

Cheers all for the help, I really appreciate it.

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