lumpy running disappears if I stop for 5mins and restart

[Gavla80]

OK, so, when I start up from cold and go for a drive there's a problem I can only describe as "lumpy running" once it gets warm, jerky acceleration (feels a bit like a misfire), or cruising along nicely at 60-65mph and suddenly starts to slow a little and then "clears" and goes normal again for a bit. I've noticed that if I pull over and stop the engine for 5 mins and restart it then this problem completely disappears and I can continue on my journey trouble free. I'm stumped!

Possibly not related but worth mentioning just in case - I've also noticed that when the engine is warmed up and idling it isn't smooth, it seems to hunt around a bit every now and then but never cuts out, is this normal?

Hopefully this description will help you to help me nail this problem... thanks in advance!

[havingagiraffe]

We had a similar problem with one of our trucks in work. Turned out to be a latex glove floating around in the diesel tank. It was getting sucked into the fuel pick up pipe when the engine was running, but dropped back out when the engine was stopped for a few minutes. Caused a lot of confusion, as you can imagine.

[CovKid]

How old are your ignition leads?

[Gavla80]

Hi, only owned the van for just under 1 yr. They look fairly new though.

[CovKid]

Well something is breaking down due to heat by your description. Common on HT leads. I wouldn't like to say that this is absolutely the cause lest I add to your expenses, but I had similar symptoms that only went away when I replaced them. Felt like it was running on 3 cylinders with naff all acceleration. Nowhere near as bad from stone cold. Kev might want to pitch in on this but he'll probably say the same.

[Gavla80]

They say made in England on them... Could well be the problem!

[kevtherev]

Do you service the van yourself Gav?

[Gavla80]

I try and do as much as I can... Learning as I go.
So far I have changed the oil, oil filter, air filter, fuel filter and all the vacuum hoses. Replaced the blower and drained, flushed and replaced the coolant... All with correct parts.

I've always wanted to learn to weld too so bought myself a welder the other day... Wife thinks I've lost the plot!

[kevtherev]

I tend to agree with Ralph, leads could cause this.
A methodical approach needs to be taken here I feel.
Eliminate the ignition probables first (Coil check, lead resistance, plug gap and grade, engine earth, earths, spark condition, hall sender effectiveness etc), and check the advance is working correctly on the distributor.

fuel, and it's delivery is your next step.

does the coil get hot after a run?

[havingagiraffe]

They say made in England on them... Could well be the problem!

Joseph Lucas. Prince of Darkness.

My money's on the coil or leads too.

[kevtherev]

I should have mentioned your choke operation.
Make sure it is actually opening fully.