Misfiring Pinto

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davidimurray

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posted on 10/12/11 at 07:22 PM

Misfiring Pinto

Any help would me much appreciated as i'm starting to reach my wits end with my Pinto

Currently engine is in the car, but no propshaft so not driven yet. Currently I'm just running the engine under no load.

Engine is an 1800 from a 1987 sierra, which had covered 44,000 miles from new and ran perfectly (i drove it 100 miles home). The engine then sat for the best part of a year while it was clened upi and painted and the chassis completed.

I have replaced the ignition system with a Megajolt setup. I have also fitted respaced ZX6R carbs

The problem I have is that I have an intermittent missfire which also spits back through the carbs. The spitting is primarily through carb 1 and 2, but can occasionally happens on the others. I have a wideband lambda fitted which read around 14 at idle and when revved.

I've swapped the spark plugs around and the spitting doesn't move. I've also fitted new ignition leads and a new coil with no improvement. I have reduced the gap between the VR sensor and trigger wheel to 0.75mm from 1mm and I've also added some extra strenghtening to the bracket to ensure the sensor is rock solid. I've tried varying the spark plug gap between 0.6 and 1mm. Checked the timing with a strobe and it all looks correct. I'm using a map I got off the internet but also tried a flat 10 deg map and the same thing happened.

I've checked the timing marks and they correct. Took the rocker coverand checked the the valve clearances and all ok.

Carbs have been balanced and are close (not perfect and need a little work)

Would float levels be a possible cause of this? Checked mine before leaving the garage with the clear tube method and there was quite a difference between them. Does anyone know what the float settings are for them?

Any help would be much appreciated beofre I tear my hair out.

Cheers

Dave

deltron63

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posted on 10/12/11 at 08:36 PM

megajolt and a coil ? double check all the wiring to the jolt, some wires might be wrong

steve m

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posted on 10/12/11 at 08:47 PM

Can you put at least one item, ignition or fuel back to stock?
so you can eliminate one side of the problem

Steve

r1_pete

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posted on 10/12/11 at 09:07 PM

Sounds like an air leak in the diaphragms on the offending carbs.

Last time I had a problem with diaphragms I smeared the jointing faces of the carb tops, and partially filled the locating groove with red rubber lube.

Also check the diaphragms aren't split.

Autosri

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posted on 10/12/11 at 09:18 PM

14 sounds quite lean mate I have tuned mine for 12.5 and it's fine and runing 14 degrees advance at idle

omega 24 v6

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posted on 10/12/11 at 10:09 PM

spitting back is usually running lean or timing out ( valve or ign). You nmight have butterflies that are not balanced yet as well.

If it looks wrong it probably is wrong.

Craigorypeck

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posted on 10/12/11 at 11:36 PM

sounds lean... 14afr at idle ok.. when reving should be near 12.5 as said.

move the needle clips down a notch and try again. if you cant adjust needles get a washer kit and place washers under clip.

check custom manifold to head face for seal, check the hoses holding the carbs on for leaks too.

float bowl height has a big effect on the fuelling , right across the rev range.. make 1,2 the same as 3,4.
You can check the float droop heights against each other

try an engine cut when the engines misfiring and check plugs

HTH

davidimurray

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posted on 11/12/11 at 01:55 PM

Thanks for the suggestions.

I will check the diaphragms in the carbs. They all seem to lift together and have a similar amount of resistance when lifted and allowed to return.

I have now found (hopefully) the correct float settings so will set them correctly and see how things go. Interestingly the two carbs that spit back the most have the highest float levels - I would have thought that over high float levels would lead to over fuelling ??

With regards to the AFR reading as 14.7 is Stoichiometric I would have thought that figures around here would be ok with no load on the engine. I can understand running an AFR of around 12 when under load.

I will have another play and richen things up when I'm back down the garage on tuesday.

One ridiculous thought I have had is that i've yet to fit a tank breather to the fuel tank so will leave the cap off and see if that makes any difference.

Thanks again for the advice.

Cheers

Dave

Autosri

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posted on 11/12/11 at 02:31 PM

type this into google

An Alternative Way of Extracting the Best Tractability and Performance from the Weber DCOE Carburetor

the top link is a pdf by innovate motorsport its a really good and clear way to tune

jacko

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posted on 11/12/11 at 04:59 PM

Don't laugh but what fuel pump are you using ?
is it a bike pump ?
could it be over fueling
I don't know anything about Megajolt
Jacko

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posted on 11/12/11 at 06:44 PM

Bike carbs often spit back especially when cold. Does it do it when hot? Try pulling choke out a little to see if any change.As said try for air leaks.

davidimurray

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posted on 11/12/11 at 07:51 PM

Thanks for the link AutoSRI.

The pump is a ZX6r pump from a carbed bike so should be ok.

The missfire is there consistently but the spitting back is occasional and erratic, sometimes you wil get a constant rapid spray blowback, other times it will do one every 30 seconds or so.

Xtreme Kermit

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posted on 11/12/11 at 08:27 PM

What speed are you idling at and what timing does that represent?

The maps I have seen are usually about 14 degrees at idle with an engine speed of about 1000rpm.

You may find you get spitting if you are too lean or don't have enough advance.

Craigorypeck

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posted on 11/12/11 at 09:10 PM

Post up your MJ map to we get a juke

edit- you sure the MJ is actually working and its not stuck on the edis limp home mode?
Check with timing light on crank when revving just to see..

[Edited on 11/12/11 by Craigorypeck]

davidimurray

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posted on 11/12/11 at 09:38 PM

At the moment I'm running at about 8 deg idle at 1000rpm as per the standard settings for unleaded in the Haynes manual. The megajolt is working as you can clearly see the marks move when you rev the engine.

I've also tried seeting the whole map to 10deg across the board and it behaved the same.

Haven't got a copy of the map here but will post one when I next get down the garage.

Cheers

Dave

Craigorypeck

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posted on 11/12/11 at 09:54 PM

edis runs wasted spark, did you try swapping 1&4 and 2&3 at the coil pack?? would eliminate the megajolt altogether as an issue wouldn't it?????

i really think its fuel related...

[Edited on 11/12/11 by Craigorypeck]

Xtreme Kermit

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posted on 11/12/11 at 10:32 PM

8 degrees is the standard with the vacuum advance disconnected I think. You need more than this.

davidimurray

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posted on 12/12/11 at 09:30 PM

Thanks fot the tips guys - I will have a look at the map tomorrow and give it some more advance. Just been having a look at the Des Hamill book and he states 12-14 degrees for a standard cam at idle so I it looks like I'm way of the mark! Should get over to the car tomorrow so will have a play and report back.

Cheers

Dave

Craigorypeck

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posted on 12/12/11 at 11:59 PM

heres a very early TPS map from my old pinto.. not proper mapped but basically what I thought a dizzy with vacuum would be doing to get me started.. bit of extra advance down low to help idle when cold.
might be of help

[Edited on 12/12/11 by Craigorypeck]

davidimurray

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posted on 14/12/11 at 09:18 AM

We have some progress

Firstly thanks for all the help and advice.

Went over to the garage last night and attacked the float levels - got them closer but still not perfect. Added some fuel with the idle screws and fired her up. Then got to work with the vac gauges and worked through carefully rebalancing the carbs -I've only got a pair of gauges as I've only ever owned 2 cylinder bikes so it takes some time. Although not perfect it is running a lot lot better now - even managed to get the 20p piece stood on end on the rocker box for 20 seconds or so!

Xtreme Kermit

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posted on 14/12/11 at 07:33 PM

Excellent! Glad you are making progress.

p.s. good photos is the FB links, where did you get the shift light pcb from?

[Edited on 14/12/11 by Xtreme Kermit]

davidimurray

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posted on 14/12/11 at 08:27 PM

Thanks Xtreme-kermit

The lights are from autosport labs - Shift Lights

Xtreme Kermit

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posted on 14/12/11 at 08:38 PM

They look good. I might get a kit to add to all the other stuff I have sitting in the garage not fitted to the car

Craigorypeck

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posted on 14/12/11 at 10:45 PM

Glad its coming round, what bout the misfire at higher revs?

I like this shift light idea very tidy.

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