Slight misfire - trouble ahead?

[shytot4x4]

I've just done my first 'major' trip (Leeds to Portsmouth and back) since I bought my '00 Ex about 6 months ago. I've noticed what feels like an intermittent and very, very slight misfire when maintaining a constant speed above about 60mph and below 80(ish) mph. That's any speed between those figures, just as long as it is a constant speed. The misfire is a 'total' miss, and not like a single plug going off for a moment and it is so slight that my passenger thought the small 'jolt' was a bump on the road surface. It would happen 4 or 5 times in a minute and then not happen for 15 mins or more. Nor did it happen during a sustained spell of 90 mph cruise controlled driving between Sheffield and Leeds (sorry officer). I never noticed the rev counter twitch, either. I used 2/3 of a tank of Tesco unleaded on the outward journey and filled up with Shell Optimax for the return trip (had an idea it might have been duff fuel...)
Anyway, to cut a long story short I once had something similar but much more drastic on a Ford Granada I used to have. That was traced to a faulty throttle position sensor. It only went wrong when the throttle was held in a constant position for any length of time...
Has anybody ever had similar probs with 4.0 SOHC Exs? I'd hate to put it into my Ford dealer with this type of prob as they don't seem to have much idea about Explorers and I just know it would cost an arm and a leg to sort it out.
BTW, Ford never found the Granada problem despite 2 days of expensive diagnostics. A local auto electrician had it sorted in less than 2 hours...

TIA
Simon H

 

[Jon Burns]

Try a new set of plugs. People never seem to change them and they don't last forever. I had really bad misfire on a trip to Germany not long after I bought the car. Got it into a German Ford dealership who changed the plugs and that fixed it. (They're due another change now as it happens). It's usually something simple, even on a car this complex.

Hope this helps.


Jon

 

[shytot4x4]

Thanks for the reply. The plugs were changed about 6 weeks ago at 42,000 miles (approx 20,000 miles early for platinum plugs). I have considered putting the old ones back in but as I have said - the 'miss' is a complete 'kick in the ass' miss and not just a sort of flat spot that might be caused by a single plug going off for a moment.
The truck seems OK on daily commuting runs so I'll probably forget about it for now until my next long journey - and I dunno when that will be... prolly after Christmas...

Simon H

 

[karl_burns]

I have the exact same issue on my OHV, and my plugs are not even 10,000 miles old.
Any other ideas everyone?
Thanks for the help.
Karl

 

[XoticXplorer]

Missfire...

Guys,
I am having a very similar problem... at a steady throttle i will get what seems to be a missfire... clunky at that like i hit an animal..

Also, it will sometimes turn over when i try to start it, and other times it will take a good 20 seconds of trying to ignition it... also, if i take my foot off the pedal and it drops below 1.5k RPM it will just straight cut out...

any suggestions?

P.S. this started to happen in the winter... constantly below 30 degrees F
and the colder it is the worse it seems to be.

Thanks in advanced

 

[karl_burns]

I had a plug go bad and throw an error code. Replaced, and it runs better, but still has that same surging / misfire feel.
I think it's my fuel filter. OEM still in there with 95K miles. That's going to be my attempt at a $10 solution. After that....ugh... I don't even wanna think about chasing something down with ice all over the roads for the next four months.
Karl

 

[XoticXplorer]

to give a lil background...

I just put a Brand new crate motor in her (have 127k on the truck, but only 14k on the new motor)

the plugs came with... so did the cap and rotor

and i had to "ghetto rig" the secondary air because we broke the standard one hah

but anyway.. i doubt its the plugs... and i recently changed the plug wires.... oh another thing.. we put the manifold gaskets on upside down and had to cut them so that the plug wires would go on

 

[XoticXplorer]

and i havent changed the fuel filter either haha

i bought one just havent had the time to replace her... i doubt that is the problem tho...


im gearing towards the TPS... i dunno any help is appreciated guys Thanx!

 

[XoticXplorer]

welp... put in a new TPS and no luck....

i have further diagnosis however... in park, at or around 1k RPM it will cut off due to the missfire... but every RPM until about 4.5k RPM it fires fine... when it gets to 4500 it will missfire pretty religiously

 

[Dave P]

Have you thought about the inlet gaskets? I had the same problem on my old Cossie. It used to run like a bag of spanners in a washing machine until I replaced it. It used to misfire, lack power and generally be undriveable. Don`t know if it helps?

 

[Howard]

we put the manifold gaskets on upside down and had to cut them so that the plug wires would go on

This sounds like the culprit.

 

[bushman8]

Ive had the same problem with my 98 explorer and an erratic tickover when cold. seemed to cure it when i put some injector cleaner in the tank and stopped using my local tescos for fuel cos there was always a rumour that their petrol storage tanks let in water when it rained, so i put it down to bad fuel.