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Author: Subject: Miss Fire 3500rpm under load
mark.silcock

posted on 27/6/19 at 11:09 AM Reply With Quote
Miss Fire 3500rpm under load

The setup is Zetec RS1800 Twin 45DCOEs Nodiz Pro

We have a misfire at approx 3500rpm under load in all gears, when the the car is stationary the engine will rev higher but still starts cutting out around 4000rpm.

Initially thinking it was a fuelling issue. Things we have triple checked is jet sizes, venturi sizes, pump jets, float levels, and fuel pressure.

Jets etc installed:
34mm Chokes
50 F11 Idle Jets
145 Main Jets
170 Air Correctors
F16 Emulsion Tubes
4.5 Aux Venturi
40 Pump Jtes
200 Needle Valve
Facet Posi Flow 4-7psi Fuel Pump
Filter King Fuel regulator

Nothing has improved the issue so now looking at spark issues.
The Nodiz Pro has decided to be very unstable connecting to the laptop over bluetooth but the map loaded is for a 2.0 Zetec on carbs supplied by Nodiz.

Planning on double checking the timing this weekend.
Spark plugs are new.

Could be coil pack or HT leads?

Has anyone got any other suggestions?

[Edited on 27/6/19 by mark.silcock]

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talkingshte

posted on 27/6/19 at 11:28 AM Reply With Quote
Check for corrosion or possible short circuits on your ignition circuit. Has the car been mapped at all? It would be good to get an idea of the air/fuel mixture as it stands.
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mark.silcock

posted on 27/6/19 at 12:10 PM Reply With Quote
this is the map on the Nodiz
Description
Description

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COREdevelopments

posted on 27/6/19 at 12:40 PM Reply With Quote
What Crank sensor are you using? I had similar issue with my megajolt setup, using a ford CPS. It would drive fine under light throttle and die momentarily under load. Idling it would rev high under light throttle up to approx. 4k. Replaced CPS and all returned to normal.

Hope this helps.

Rob






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mark.silcock

posted on 27/6/19 at 12:42 PM Reply With Quote
Thanks, using the Zetec CPS

Will look into it.

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talkingshte

posted on 27/6/19 at 01:39 PM Reply With Quote
Am I right in saying the Nodiz only does ignition? You'll need to get the fuelling table to see if theres a problem, just get a run done on a dyno.
All engines are slightly different, so cause someone else has the same parts and it works fine, yours might need some fine tuning to get it there.
I'd start by checking the electrical side, all your sensors (cps is a good shout) make sure the alternators good, earths, everything. Then move onto the fuelling side of things.
I hope I'm not telling you how to suck eggs!

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mark.silcock

posted on 27/6/19 at 02:17 PM Reply With Quote
Yes the Nodiz only does ignition.

Planning on getting it on the dyno but would rather check everything first, dont want them chasing their tail identifying an issue if I can help it.

Dont worry any advice is good advice at this stage.

Worth noting we need to get it through the non cat emissions test for the IVA.

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perksy

posted on 27/6/19 at 04:15 PM Reply With Quote
Is this when the engine is Hot and Cold?

Is it worse when either of the above applies?

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Ugg10

posted on 27/6/19 at 04:27 PM Reply With Quote
I had a similar problem, are you using a shielded cable for the nodiz to crank sensor with the shield connected to earth at one end? I wasn’t and was picking up interference from somewhere else that was causing a similar fault.





---------------------------------------------------------------
1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
Build Blog - http://Anglia1968.weebly.com

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Schrodinger

posted on 27/6/19 at 04:39 PM Reply With Quote
Have you checked for a "Soft Cut"? in the ignition table?





Keith

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bikecarbfred

posted on 14/7/19 at 06:33 AM Reply With Quote
i had a problem like this with megajolt trigger wheel set up. the vr sensor was picking up viberation at higher rpm
one of the cables in the vr sensor was loose. not only that the vr sensor was too far away from the trigger wheel.

i re wired the vr sensor at the trigger wheel side.
i re mounted the vr sensor so it was almost touching the trigger wheel.


the way i realised it was this, was on the laptop at high rpm i noticed the rpm digital gauge would go out of synch at high rpm after3500-4000rpm.

cheers

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mark.silcock

posted on 20/9/19 at 10:13 AM Reply With Quote
So I still havent got to the bottom of this issue, have thrown at it new coil pack, leads, plugs, main jets, idle jets, chokes, needle valves, pump jets, fuel pump and nothing has made a difference. Engine temp doesn't make a difference.

Spoke to Nodiz and they dont believe its an issue with the ECU as it is only running off the crank sensor so the unit cannot detect any engine load, and seeing as it can rev fine with no load up to the limiter the unit is working as it should. Also the crank sensor seems to be fine. Have checked the soft cut settings and the launch control setting on the Nodiz and nothing is set to around the 3500rpm.

Other things I have tried are used a colourtune to tune the idle adjustment, sync'd the carbs, checked float levels, set the fuel pressure at the last carb to 2.5psi..... think that is about it.

So the assumption now is that the carbs need rebuilding, or I might go EFI as I have a Ginetta intake manifold and fuel rail sitting in the garage. Only issue with that is it would need a new ECU and fuel pump, also getting it under the bonnet will be a challenge.

Well that was more a of a vent than anything else but open to any suggestions....

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jeffw

posted on 20/9/19 at 10:15 AM Reply With Quote
It will be the crank sensor, either it is faulty, too far from the crank wheel or not screened correctly. Change it for a start.

[Edited on 20/9/19 by jeffw]

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RichardB123

posted on 20/9/19 at 10:17 AM Reply With Quote
I dont see how its possible for a carburettor to cause a missfire like this.
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mark.silcock

posted on 20/9/19 at 10:18 AM Reply With Quote
quote:
Originally posted by jeffw
It will be the crank sensor


Why would load affect it though?

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RichardB123

posted on 20/9/19 at 10:19 AM Reply With Quote
What has changed since it was last running correctly?
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RichardB123

posted on 20/9/19 at 10:20 AM Reply With Quote
quote:
Originally posted by mark.silcock
quote:
Originally posted by jeffw
It will be the crank sensor


Why would load affect it though?


An ignition system is working hardest under load.

Just revving it up not in gear, the spark can be very weak or late/early and it would still sound OK

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mark.silcock

posted on 20/9/19 at 10:26 AM Reply With Quote
quote:
Originally posted by RichardB123
What has changed since it was last running correctly?


That's one of the annoying things, it was purchased as an unfinished project and I never drove it in anger so dont know if it was like that previously.

I changed the engine from a 1997 1800 silvertop to a 91 RS1800 to get past the emissions other that that everything is as it was.

Looking through the previous owners diary and receipts he also spent a bit on servicing the carbs and different jets so I suspect it may have never run right. Also only paid £250 for the pair off ebay which seems cheap. He was going to put bike carbs on it.

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mark.silcock

posted on 20/9/19 at 10:29 AM Reply With Quote
quote:
Originally posted by RichardB123
I dont see how its possible for a carburettor to cause a missfire like this.


It just feels and sounds like fuel starvation.

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mark.silcock

posted on 20/9/19 at 10:34 AM Reply With Quote
quote:
Originally posted by RichardB123
quote:
Originally posted by mark.silcock
quote:
Originally posted by jeffw
It will be the crank sensor


Why would load affect it though?


An ignition system is working hardest under load.

Just revving it up not in gear, the spark can be very weak or late/early and it would still sound OK


Will try one.

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perksy

posted on 20/9/19 at 06:23 PM Reply With Quote
Does it missfire when the engine is hot or cold or does it make no difference?


I'd agree with Jeffw though and say Crank sensor

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gremlin1234

posted on 20/9/19 at 08:15 PM Reply With Quote
quote:
Originally posted by mark.silcock
quote:
Originally posted by RichardB123
I dont see how its possible for a carburettor to cause a missfire like this.


It just feels and sounds like fuel starvation.

first check the fuel filters,
and as always, ensure the fuel is reasonably fresh, and charge the battery.

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SPYDER

posted on 20/9/19 at 08:37 PM Reply With Quote
In an earlier post you said..."it is only running off the crank sensor so the unit cannot detect any engine load, "
So to be clear, it has no TPS or MAP sensor?
Or am I missing something?
It wouldn't be the first time.
If it was forced induction I might suggest reducing the spark plug gap. Worth a try?
I had a similar, but admittedly non load dependant misfire on my Megasquirt install, which was cured by
putting a 10K resistor in line with the VR sensor.
Float bowl fuel levels correct?
Many coil packs have an associated suppressor/capacitor attached? Does yours? Should it have? Is it faulty?

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perksy

posted on 20/9/19 at 09:12 PM Reply With Quote
Faulty Battery isolator switch ?

Although they usually cause a high speed/RPM missfire...

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mark.silcock

posted on 22/9/19 at 07:16 PM Reply With Quote
quote:
Originally posted by perksy
Does it missfire when the engine is hot or cold or does it make no difference?


I'd agree with Jeffw though and say Crank sensor


Engine temp doesn't seem to make a difference.

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