Throttle hesitation

[AdamC3046]

Hi guys

I recently bought a 350i, and I drove it quite a lot yesterday, and throughout the day I noticed a problem develop.

The car was hesitating when I was cruising at a constant speed. To accelerate it would stutter a bit to get out of the hesitation phase, and then accelerates fine.
It got worse and worse throughout the day until it got to the stage that even in 1st gear pulling away, and through the gears slowly it would hesitate a lot. Very similar to fuel starvation or ignition problems.

I let it cool down a bit and it ran better, and it still ticks over and accelerates really well.

A separate problem on the day was it kept popping out of 4th gear

Any ideas?
Thanks in advance.

[KKson]

AdamC3046 said:

Hi guys

I recently bought a 350i, and I drove it quite a lot yesterday, and throughout the day I noticed a problem develop.

The car was hesitating when I was cruising at a constant speed. To accelerate it would stutter a bit to get out of the hesitation phase, and then accelerates fine.
It got worse and worse throughout the day until it got to the stage that even in 1st gear pulling away, and through the gears slowly it would hesitate a lot. Very similar to fuel starvation or ignition problems.

I let it cool down a bit and it ran better, and it still ticks over and accelerates really well.

A separate problem on the day was it kept popping out of 4th gear

Any ideas?
Thanks in advance.

I'd start with checking the HT side of things. I had a load of issues last year with a misfire that got worse as the engine warmed up. Start off with simple things like rotor arm, distributor cap, coil and HT leads. Just check one thing at a time rather than a scatter gun approach.

[Rockettvr]

There's lots of advice here:- http://www.vintagemodelairplane.com/index.html with regards the efi and ignition systems
I had issues with hesitation and it was the fuel pressure regulator starting to fail so check that you've decent fuel pressure also
Good luck

[wedgewood]

Be interesting to see what ideas come up from this thread. I have the same symptoms on my 350i, on an even throttle at lowish speeds eg 1500-2000 rpm the engine hesitates, feels more like fuel than spark, its not a misfire but its like the fuel supply is momentarily dropping, accelerate and the problem disappears. I would welcome suggestions... mean time i'll look at the fuel regulator.

[v8s4me]

AdamC3046 said:

...The car was hesitating when I was cruising at a constant speed. To accelerate it would stutter a bit to get out of the hesitation phase, and then accelerates fine....Very similar to fuel starvation or ignition problems....

When was the fuel filter last changed?

[wedgewood]

dare I say it 10 years/ 700 miles ago! I have just put a pre-filter on in the last few months but this is not a new problem, the car has always done it, its just that I saw the thread and wondered if as Boycie would say 'they all do that'

[mrzigazaga]

Well i have had a similar issue...Actually it was more than one...

1. I had a mis-fire at 2500-3000 rpm when it was warmed up..That was crossed wires in the CTS plug..I would check the CTS for resistance hot and cold.
2. I had one where it didn't matter what the temperature was and that used to happen randomly and that was a fuel pump loose wire...While its running just wiggle the wires at the pump and if it stalls then there is the fault..
3. Hesitation at all rpm's except idle..That was fine..It would be okay after a few revs and would clear but then one day it would not rev at all and even back fired when i tried to keep it alive with the throttle...This turned out to be a loose ECU plug..

The other day i removed the ECU plug and cleaned up all the male and female connections..You can bend the pins slightly but i didn't want to do that in case i broke one so i just closed up the female connection and it now runs sweet as and feels quicker than its ever done..No more hesitation or mis-fire!...

Hope you sort it


Cheers


Ziga

[350zwelgje]

Had this twice:
- coolant temperature sensor. Cold ok, warming up and at normal temperature later it stall due to overfuelling. This sensor is notorious even when new out of the box! Short the ends and if no problems anymore, it will be this sensor.
- idling ok, but acceleration got worse over the years. Was thinking to rebuild the engine, but resoldering the ECU and back to new and all horses came back.

But as mentioned before, the coil and rest of the ignition system brake down with heat if not ok.

Don't change to many things at the same time and keep in mind that new parts can be faulty out of the box....

Rob

[mrzigazaga]

Yes as said a couple of times..Replace part...Test car...Replace part.. Test car...Be methodical in your elimination otherwise you may sort it without knowing the cause and not being able to help anyone else in the future...

Good luck

Ziga

[celcius]

As mark says , test each component at a time

[v8s4me]

What about the ignition amplifier? Over time the paste that is supposed to insulate it from the heat coming of the distributor brakes down. Re-locating the amp using this kit might help. I'd suggest re-locating the coil while you're at it.

[hrepo]

v8s4me said:

What about the ignition amplifier? Over time the paste that is supposed to insulate it from the heat coming of the distributor brakes down. Re-locating the amp using this kit might help. I'd suggest re-locating the coil while you're at it.

The paste is not to insulate, it's the thermal paste used to BETTER conduct heat. The module is using distro body as heat sink (bad design idea).

[SLB]

hrepo said:

The paste is not to insulate, it's the thermal paste used to BETTER conduct heat. The module is using distro body as heat sink (bad design idea).

I've used the kit to move the ignition amplifier away from the heat. Heat and leaking swan neck cap killed mine and then a cheap replacement only lasted 5k miles. They resulted in misfires which varied with revs and heat. I wouldn't bother with the cheap ones and just use the Lucas one which is supplied into the kit.

I've been driving wedges for 21 years now and only ever broken down twice at the side of the road. Both times it was the ignition amp which when cooled started working well enough to limp the mile or two home.

Edited by SLB on Tuesday 6th September 23:07

[AdamC3046]

Thanks for all your suggestions, it seems like I am going to have to try one attempt at a time.
I'll take it for a long drive on the weekend to see if the problem reoccurs at all.

But for now, I've got my gearbox to repair :'(

[hrepo]

SLB said:

I've used the kit to move the ignition amplifier away from the heat. Heat and leaking swan neck cap killed mine and then a cheap replacement only lasted 5k miles. They resulted in misfires which varied with revs and heat. I wouldn't bother with the cheap ones and just use the Lucas one which is supplied into the kit.

I've been driving wedges for 21 years now and only ever broken down twice at the side of the road. Both times it was the ignition amp which when cooled started working well enough to limp the mile or two home.

Edited by SLB on Tuesday 6th September 23:07

Same. I mean, I've broken down because of the amp, and when cooled down it'd last the mile or two (or five), then need another cooling session. And I also got the kit now. And also my amp that failed was an aftermarket bit.

[v8s4me]

hrepo said:

.....And also my amp that failed was an aftermarket bit.

Was that the one in the Lucas kit? If so did it fail gradually, or just fail completely?

[hrepo]

v8s4me said:

Was that the one in the Lucas kit? If so did it fail gradually, or just fail completely?

Nah, it was the unbranded aftermarket one in the car before I got the kit. I don't know if it started to get the hot symptoms gradually or at once. The one in the Lucas kit is not "proper Lucas" Lucas, as the brand is now just a marketing stamp. I still have the original Lucas bit (was in the boot of the car, wish I knew that when I sat in Tesco parking lot waiting for the dodgy amp to cool down), am planning on testing that and then taking it into use if it still works. If not, I'll keep using the one from the "Lucas" kit. It seems fine so far, but as the car is now in bits haven't really driven it much.

Also, obligatory note that it's dark days when the Prince Of Darkness is considered to be the "reliable" supplier.

[rev-erend]

Some nice jokes about Lucas - the prince of darkness:

What better way to while away the lazy afternoon hours than with a collection of jokes, anecdotes and humorous diagrams depicting the joys of Lucas electrical systems? Joe Lucas — or, more accurately, the company bearing his name — engineered electrical bits for pretty much everything emanating from the UK, and the notorious unreliability of Lucas components played a key role in tanking the British car industry in the early 1980s. Make the jump for "If Lucas made guns, wars would not start," and other classics.

The Lucas motto: "Get home before dark."
Lucas is the patent holder for the short circuit.
Lucas - Inventor of the first intermittent wiper.
Lucas - Inventor of the self-dimming headlamp.
The three position Lucas switch - Dim, Flicker and Off.
The Original Anti-Theft Device - Lucas Electrics.
Lucas is an acronym for Loose Unsoldered Connections and Splices

This makes great reading..

http://www.mez.co.uk/lucas.html

Edited by rev-erend on Wednesday 7th September 19:20

[SLB]

v8s4me said:

Was that the one in the Lucas kit? If so did it fail gradually, or just fail completely?

My original one failed gradually starting with top end misfire/ hesitation gradually moving down the rev range. Bad hesitation around 3k and worse when hot. After a good run it just died at some traffic lights and wouldn't run until it cooled down. Similar with the aftermarket one but it only lasted a year or two and I bought it with the two pin to 3 pin conversion kit. If the "Lucas" kit one isn't a real Lucas it may be better than before beacause it's mounted away from the direct heat. Fingers crossed but I was considering carrying a spare around with me.