Misfiring/hesitation...

[Spooky]

Right, I've rejetted the carb...1.2mm main, 0.9a/c and a 1.3mm 2nd stage.

A couple of days ago, with a wideband in situ, at idle/part throttle I was seeing afrs between 13.9ish-14.5ish.

Full thottle in 4th upto 6.5k im seeing 12.1-12.3 @ 20psi at the manifold. In 5th at around 5.5/6krpm, from a quick scan the reading was leaning off, creeping into the high 12s so I backed off.

At 18psi, in 5th gear, I can get up to 6500rpm and read 12.2-12.3.

I'm using a standard cam with a t28 turbo.

Yesterday, I went out for another run.

Under full throttle condition, gear changes from 2nd to 3rd, 3rd to 4th, resulted in big hesitation at around 3krpm, I kept my foot in...which seemed to clear its throat so to speak...and then followed up with a huge misfire, hitting a limiter style lol

I noticed the boost guage roughly reading 10psi when it did this, the vac reading was very slow in rising where as before the car instantly wound out to the desired boost.

The car idles alright, its not brilliant.

I dont have direct access to the wideband as of yet as I'm borrowing it but what should I look for ?

[Andrew Cooke]

TDC sensor :P

[Spooky]

New one on there Andy

Its only started being a bitch since I tweeked the carb...

[Mart]

So you ignored my pm then

[Spooky]

Far from it Martin

I tried what you suggested, that worked in terms of idle and off boost driving.

Now this is only happening when its coming on to boost

[Chris Hebden]

Accel pump maybe? I had major issues with it this morning with hesitation and AFR's in the 9's no matter where the throttle was positioned! Fiddled with the accel arm and it cleared it self

[Jimmy_GTT]

We have similar hesitation problem whit my friend's GTT.
I also think it could be either TDC sensor or something with the carb. I have already changed the AEI but no influence.

I have read that Spooky is runnig 12.2-12.3 @ full boost.

Mine is around 13.5 is it lean? Shall I enlarge 2nd stage a bit?

[Spooky]

13.5 isn't any good to you!

whats your carb spec dude ? boost...revs...jetting etc...

[Jimmy_GTT]

13.5 isn't any good to you!

whats your carb spec dude ? boost...revs...jetting etc...

Standard carb jetting, only 2nd stage is between 1.05 - 1.1
14psi @ manifold, reving till 6.300-6.500

What would be a correct AFR?

[Spooky]

open out that 2nd stage to 1.2-1.3mm

you need to see afrs in the early 12s at w.o.t at those revs


UPDATE : i tried my carb on another car and it went like a bat out of hell!

revved upto 6.5krpm in 4th and top @ 20psi, afrs didnt move much above 12.2-12.3 at very silly speeds!

im going to try another run tomorrow in my car with a fuel pressure guage hooked up. i dont think my fuel pump is keeping up, never mind the carb lol

if the carb works on another car with the same spec, the only other area to look at would be that

could be clutching at straws but worth a go

[Kris M]

come on Sukh, get yourself a group A fuel pump !

[Jimmy_GTT]

open out that 2nd stage to 1.2-1.3mm

you need to see afrs in the early 12s at w.o.t at those revs


UPDATE : i tried my carb on another car and it went like a bat out of hell!

revved upto 6.5krpm in 4th and top @ 20psi, afrs didnt move much above 12.2-12.3 at very silly speeds!

im going to try another run tomorrow in my car with a fuel pressure guage hooked up. i dont think my fuel pump is keeping up, never mind the carb lol

if the carb works on another car with the same spec, the only other area to look at would be that

could be clutching at straws but worth a go

Thanks.
Do you think I shall try a smaller a/c? For eg. 110?
Because when I'm keeping a certain speed on the highway it leans up to high 14s.
If I remember right I had a 122.5 or 125 main jet.
What does 'w.o.t' mean?

[TrixNFlix]

W.o.t means wide open throttle.

[Jimmy_GTT]

W.o.t means wide open throttle.

Thanks mate!

[Brigsy]

Have you changed the basic ign components mate, I.e leads, plugs, cap & rotor arm.

I had a similar problem on the van, i changed the above & tdc lead/aei, the problem has never came back. I suspect my aei/coil was on its last legs.

Also my tdc lead went all soft, almost melted when the problem appeared. I renewed it & shielded it with heatproof wrap.

[Spooky]

Well, everything other than the aei has been replaced or renewed. Trying to get an aei off a mate to try later.

I've just been out again, fuel pressure is around 2psi above boost, doesn't sound high enough to me

Also, I tried a run at 10psi, no problems accelerating well into high rpms, no misfiring/hesitation. Went out again at 20psi, the hesitation came back followed by a spectacular misfire

I'll try another aei, hopefully I'll have a wideband to play with again tonight.

[James5]

Fuel pressure should be 4psi above boost pressure

[Spooky]

I knew it should've been above boost pressure, wasn't sure on how much exactly, cheers James

Ive managed to source a fuel pump, well, I'm borrowing it from a running car LOL

Something to try later this evening

[Brigsy]

Dont forget that boost should be 4 psi higher than boost at the carb top mate. If its only 2psi sounds like you may have sussed it.

[Spooky]

Well, I won't be going out tonight...my missus has organised a meet for her bridesmaids, while I'm at home with little'un

I'm hoping its the fuel pump, will know tomorrow hopefully

[Spooky]

Had to fit a kitchen today ...anyway...

I tried another fuel pump, no joy. Fuel pressure stayed approx 4psi above boost at 10, 15 and 20psi at the manifold.

I mentioned before I was seeing less pressure, I wasn't. Today, I had someone with me to read the guages while I was doing the driving and the pressure was constant at approx 4psi above boost.

I've literally changed everything bar the aei and the f.p.r, which I will do tomorrow.

I am noticing that when I boost and slow down now, the overrun is very poppy... and the car will idle very poorly trying its hardest not to conk out.

Hmm. I'll post up how I get on tomorrow

[Scoff]

It could be as simple as a weak spark if it's blowing out at higher boost. It's worth checking that the aei is getting 13v with the engine running, and that it's earth (black wire in 3 pin plug) is good also.

[Scoff]

On a similar note, check for dodgy/crapy wiring around the over boost relay. better still, bypass it completely.

[Spooky]

Scoff, thinking about it now, its similar to the overboost cutting in at higher rpm. Good thinking

I'll give it a bash in a bit

[Jimmy_GTT]

I am noticing that when I boost and slow down now, the overrun is very poppy... and the car will idle very poorly trying its hardest not to conk out.

Hmm. I'll post up how I get on tomorrow

Had a similar issue with my friend's 5. After 2 days the little thing which was in the carb landed on the idle jet causing no idle at all. Than I removed the idel jet take out that little thing (I do not know what it was) after that car idles fine and do not have that poppy overrun.

[Spooky]

UPDATE :

I changed the aei this afternoon, literally just this second got in from a lap round town etc and the car appears to be back to normal. I ran the car at 1 bar and it drove without a glitch

I didn't check the voltage because my voltmeter had packed up, typical.

I need to do a few more longer runs at 10 and 20psi as I've had quite the busy weekend and no one with me to watch the guages

Getting there.

I will be going to Pod on the 17th damn you

[Spooky]

W@nky car...

Started the her up today, started fine, idle dropped off so I held the throttle until she held a steady idle.

I left the car for a few mins to heat up a bit, came back outside and the bitch had stalled.

No bother, went to fire it up again...turned over fine a few times before it started to misfire...coughs, splutters and spits back through the carb...and then refused to start altogether.

I have no idea what the car is doing as its ran really well as of late... ...

But I would imagine this is timing/ignition related

[JRP]

Could it be an air leak, like on the carb base or alike ?

[Spooky]

Hmm...new gaskets on the base, inlet mani gasket was changed too.

When it did run, it sounded like it was running on 3 but the misfire seemed to clear the more revs I gave it.

[JRP]

you know the bottom gaskets, i always put a lick of sealent around them, to the inlet and carb base... people may say you dont need to, you could try this see if it helps. mine did whats yours is doing well an old 5, thats how i cured it.

The more you rev the more air it needs anyway so i guess the air leak would become un noticable.... i could be mega wrong tho

[Spooky]

I know what you mean dude

[Shane P]

Mine started doing that a couple days ago, turned out oil had got under the dizzy cap after i blew my oil cooler pipes and had burnt onto all the terminals !

[Spooky]

I'll stick another dizzy/rotor arm on there tom.

I gave up on it a while a go

[James5]

I'll stick another dizzy/rotor arm on there tom.

I gave up on it a while a go

Have you had the dizzy shaft out at all if so may be you have knocked the dizzy gear a tooth out?
Whilst your checking / replacing the dizzy might be worth making sure it is in the correct position when at tdc using the flywhhel tdc mark and the gearbox bell housing 0 tdc marking.

[Spooky]

James, not had the drive out but the misfire is identical to that of when the leads are fitted 180 deg out

I'll get it all out and check to see if it's all ship shape and timed up as it should be

[Spooky]

I dont want to ditch the carb'd engine but on nights like this I can't wait to start the 2ltr conversion.

I left the window open from earlier, turned the key and the car started fine...no misfire or anything so I decided to go for a drive...guess what, no issues

I'll still fit a new dizzy/rotor arm, may as well get plugs & leads while I'm there

Stupid car

[James5]

I dont want to ditch the carb'd engine but on nights like this I can't wait to start the 2ltr conversion.

I left the window open from earlier, turned the key and the car started fine...no misfire or anything so I decided to go for a drive...guess what, no issues

I'll still fit a new dizzy/rotor arm, may as well get plugs & leads while I'm there

Stupid car

Fecking C1J's it is makeing sure you don't forget about her

Weird thing is this time last year I was doing the 172 conversion and had the engine in but not running https://www.rtoc.org/boards/showthread.php?t=2578.

Have you worked out what you are going to do for a bonnet with the 172 lump underneath as the only real option is the 16v hump or maybe a custom plenium but then that's £££'s

[Spooky]

I was chatting to my missus about that, everytime I leave it on the drive and take the 172, I always have an issue when I go to drive off in the 5

In terms of the bonnet clearance issue, if I can squeeze throttle bodies in there and keep the oe bonnet, I'll be doing just that!

I'd rather spend money on throttle bodies than a custom inlet mani.

[Mart]

Could be a sticking valve.

Just out of curio', which cam is in situ?

[Spooky]

Mart the cam is standard, as is the rest of the engine inc the headgasket etc

[Spooky]

Can't confirm its age/condition though as Ric had it changed when he had a 'rod let go on him.

I would imagine he never gave the engine a work out like I've been doing as of late

The backfiring sounds like a timing fault like I said before, like when the leads are incorrectly fitted but I've never thought about a valve sticking...

I'm just waiting for the missus to get home with some new leads, cap/rotor arm then go and see if it starts and runs alright.

If not, I'll get the head off and get the old valve grinding paste out

[Mart]

I was thinking an overlap/blow back scenario if you had some extreme cam in situ, but it's an o.e stick, so that eliminates that.

Defo worth eliminating the valves from the equation, be it sticking or not fully sealing.

[Spooky]

Thats all I've got left to investigate I think.

Everything else has been changed/renewed in terms of ignition and fuelling

[Spooky]

Just needed a good drive! Does't like being sat for a week LOL 20psi...all is GOOD!

[Ricardo]

That C1J lump was sound as a pound when Rob dropped it in for me Mart THE carb ledge did his work when i had it booked on Track N Road rollers and gave us a respectable 174bhp and 176ft/lbs

[Spooky]

That C1J lump was sound as a pound when Rob dropped it in for me Mart THE carb ledge did his work when i had it booked on Track N Road rollers and gave us a respectable 174bhp and 176ft/lbs

The engine is fine...just doesn't like being sat about, THATS when I get the grief

[Ricardo]

The engine is fine...just doesn't like being sat about, THATS when I get the grief

I still say check those spark plugs,not what make they are but the condition

[Spooky]

Its fine, shes started up outside now, warming up a bit, going shopping via the scenic route

[Ricardo]

Its fine, shes started up outside now, warming up a bit, going shopping via the scenic route

Blow some soot off them!