Ls400 Engine Trouble

[soundchaser100]

Up until Tuesday of last week my 96 Ls400 was running perfectly. I have recently replaced the spark plugs and leads with the correct types bought from Rock Auto. On Tuesday I drove down to Ironbridge , all going very well until I stopped to fill up with Esso near Whitchurch. Set off again, but after about 10 miles the engine developed a bad misfire. On tickover the engine is very lumpy, it has to be revved to over 2500 rpm to get it to run evenly. Under drive conditions, it will accelerate fairly well on near full throttle but around 30 - 40 mph it misfires terribly and can be felt to surge as the number of cylinders firing goes up and down. It feels very short of power but hasn't stalled yet. Could this be a case of bad petrol or just a coincidence ? I have had the top cover off the engine and checked all vaccuum pipes and leads etc. Anybody got any ideas? Paul

[Nitmoi]

Faulty earth or fuse?

[steve2006]

Hi,

Is the EML on indicating a fault?.

Sounds a bit strange after just filling up with fuel could be water contamination in the fuel or it could be just coincidence.

If it were electronic I would expect the EML to be on.

Does the UCF20 have distibutors and rotor arms like the UCF10?

Also check the cats after running for a while if they are glowing it normally means unburnt fuel is reaching them confirming a misfire.

[soundchaser100]

Hi,

Is the EML on indicating a fault?.

Sounds a bit strange after just filling up with fuel could be water contamination in the fuel or it could be just coincidence.

If it were electronic I would expect the EML to be on.

Does the UCF20 have distibutors and rotor arms like the UCF10?

Also check the cats after running for a while if they are glowing it normally means unburnt fuel is reaching them confirming a misfire.

Thanks for your reply.

No, the EML is not on. I find this a little odd as there is definately a misfire.

Yes the UCF20 does have rotors and distibutors. I have checked these, all looks OK. After a short run yesterday, I could hear the exhaust system ticking much more than usual as the car stood outside the house. This would confirm that the cats are getting much hotter than usual. I think I need to drain some fuel either from the tank or from the fuel line on engine to check for water. Paul

[steve2006]

Another thing you could try is to run the engine at night and have a look under the bonnet for any signs of HT tracking on the leads.

[soundchaser100]

Another thing you could try is to run the engine at night and have a look under the bonnet for any signs of HT tracking on the leads.

The leads are brand new, Steve, and in any case , it was running fine until I put the fuel in. The more I think about it, the more it looks like water in the fuel. What do you think would be easier, drain the tank or connect a pipe to the fuel rail under the bonnet. If it is water, it will be sitting at the bottom of the tank, so I should see it in any fuel I remove.

[Matrixabc]

you may be able to syphon the water out from the bottom of the tank? if the car is on level ground. or park on an incline and get the pipe to the lowest edge of the tank. Assuming they don't have an anti syphon system fitted.

[kenmac]

Any more on this as mine is now doing the same,but mine has started after the heavy rain over the last few days.

[kenmac]

I've tracked mine down to a duff plug.

[flotsam]

The closest to my experience was a fuel filter which regularly clogged in my Vauxhall Sports Hatch. I then avoided petrol stations where there was a filler truck as they tend to stir up the scum on the bottom of the fuel vat at the petrol station.

I had a fuel problem with a volkswagen Golf too. The crooks at volkswagen claimed the whole system needed replacing,

[whataniceman]

Up until Tuesday of last week my 96 Ls400 was running perfectly. I have recently replaced the spark plugs and leads with the correct types bought from Rock Auto. On Tuesday I drove down to Ironbridge , all going very well until I stopped to fill up with Esso near Whitchurch. Set off again, but after about 10 miles the engine developed a bad misfire. On tickover the engine is very lumpy, it has to be revved to over 2500 rpm to get it to run evenly. Under drive conditions, it will accelerate fairly well on near full throttle but around 30 - 40 mph it misfires terribly and can be felt to surge as the number of cylinders firing goes up and down. It feels very short of power but hasn't stalled yet. Could this be a case of bad petrol or just a coincidence ? I have had the top cover off the engine and checked all vaccuum pipes and leads etc. Anybody got any ideas? Paul

hi did you cure it if so how i have the same problem

[soundchaser100]

Up until Tuesday of last week my 96 Ls400 was running perfectly. I have recently replaced the spark plugs and leads with the correct types bought from Rock Auto. On Tuesday I drove down to Ironbridge , all going very well until I stopped to fill up with Esso near Whitchurch. Set off again, but after about 10 miles the engine developed a bad misfire. On tickover the engine is very lumpy, it has to be revved to over 2500 rpm to get it to run evenly. Under drive conditions, it will accelerate fairly well on near full throttle but around 30 - 40 mph it misfires terribly and can be felt to surge as the number of cylinders firing goes up and down. It feels very short of power but hasn't stalled yet. Could this be a case of bad petrol or just a coincidence ? I have had the top cover off the engine and checked all vaccuum pipes and leads etc. Anybody got any ideas? Paul

hi did you cure it if so how i have the same problem

Hi, yes I did cure it,or at least Lexus Chester did. It turned out to be the spark plug leads which were nearly new and I had bought from Rock Auto in the states. The took the car to them for a new cambelt and asked them to find the fault, they did, it cost me £1100 to learn not to fit non-Lexus parts!! Paul