420 sec fuel problem

[secman]

my car is a 420 sec 1987 runs lumpy from a standing start as engine rpm increases runs ok.I can smell fuel inside the car and from rear of car as a friend told me who was following me at low speed in his car. it seems like overfuelling any ideas,many thanks.phil

 

[guydewdney]

iirc these had a problem with the fuel pressure regulator - they are cheap (20 quid?) and easy to fit..

temp sensor could also be to blame - if the ecu thinks its cold, it will over fuel (the sensor for the dash is a different sensor to the ecu one) - again - easy and cheap to replace (big 'bolt' at front of engine - ?2 wires to it)

o2 sensor also - exbenzive to do... get a diagnostic before going down this route..

new plugs will probably help - if one / 2 are down then it will run lumpy and smell of petrol. - ditto dizzy cap / leads.


well - theres somthing to be getting on with this w/e

 

[talbir]

Guy is spot-on with the suggestions.

The fuel pressure regulator has a vacuum line coming into the rear of it - it is usually here that it begins to leak. At which point it does not maintain correct fuel pressure. Check for signs of fuel around the vacuum line where it connects to regulator.

Also, check the EHA 'guvnor' on the side of the fuel distributor. This can also go faulty and leaky. May need to renew copper washers beneath the screws holding it to the distributor.

Temp sensor on manifold - may have a 4-pole plug, which most of the later models did.

I don't think an 87 would have an O2 sensor though, as cats were introduced late '90 ?

Plugs are crucial - especially the gap. The w126 V8's like a big gap for a smooth idle, usually 0.040" for the 420's and 500's. 0.045" for the 560's.

Before anything have the mixture checked on the machine to ensure CO is at right level.

talbir

 

[secman]

thanks guys,I recently had emmissions checked and was told co was high,does this make any difference to the items you have told me to check.many thanks .Phil

 

[talbir]

Did they adjust the CO to the correct level ?

If they did and it's still a problem, then it's really a step-by-step process of checking all the above and perhaps more. IT's a testing process - and only replace an item once it has been diagnosed as faulty. Trial and error is not the way.

You may also have an air leak which would cause car to run rich and give the lumpy idle + high CO you mention. Check the rubber hoses running along the injectors and all rubber tubing under the air filter housing.



talbir