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Superspec misfire and idle speed


geordie40

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Hi all

My superspec has developed a very intermittent misfire (I think) and the idle speed has risen from 900rpm to around 1100.

The misfire or whatever it is has always lurked about, it can happen when just tootling along and then all of a sudden theres a slight hiccup as if my foot slid off the accelerator or it will happen when I'm giving it some beans overtaking something which is a little scary especially when something is coming the other way !!

So I decided to clean the throttle assy with some carb cleaner ( gave it a good few squirts) and now my idle speed has increased and changing the idle value in the ecu doesn't seem to make a difference, ohh and a little more difficult to start from cold.

The car has had new coil, leads and plugs (fancy platinum ones, may put Billy basic back in to see).

All ideas welcome

On the plus side ive fixed the clonk on pulling away (2 loose bolts on propshaft) and the play in wheel bearing (centre but not tightened sufficiently)

1 step forward and 2 back 😣

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Guest MrToad

Sounds like a possible leak in the intake side of the engine. Check all the vacuum tubes for leaks, make sure carb and intake manifold are properly fastened down.

I made up my own smoke box using air conditioning system smoke pellets, found leaks where I didn't expect them.

Air leaks will cause the engine to run faster at tick over due to more air being allowed in than the carb controls, also makes mixture extra lean so will be harder to start, plus will make the mixture wrong all over making general running erratic.

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Thats what i was thinking but it doesnt have carbs its a 2L fuel injected rover engine (T series), I have re checked everything I took off which was only the cold air induction intake but i suppose the tube may have split, will take another look

Edited by geordie40
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Will do alan, looked at it the other day but dont know what im looking for. I still get a TPS error on the mems but its been changed.

Do you know if disconnecting the battery has an effect on the ecu memory as my battery isolation switch is on the -ve so when i remove the key everything is dead

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Check the cable and linkage on the throttle body, especially if you've been cleaning and playing around in that area. I had a similar high rpm problem that turned out to be the throttle cable not seated properly in the groove on the underside of the quadrant. My cable had a very small brass ferrule on the end, which had got lodged in the quadrant and was holding the cable off so the butterfly wouldn't shut properly.

Also check that the butterfly is completely closed at idle and adjust the cable so there's just a touch of slack before the linkage moves.  I found you only need a tiny amount of over-adjustment of the cable to slightly open the butterfly and increase the rpm.

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I also had the same as Andy - the rubber boot over the cable at the quadrant end got in the way of the cable around the quadrant.  Thus quadrant couldn't shut properly, hence higher idle.

In my experience on a tin-top, hiccup of power was caused by brief loss of fuel.  In my case, dirt in fuel tank.  In the SuperSpec you could check 12v to the fuel pump (wire a multi-meter across fuel pump and have it on the dashboard - watch when you get hiccup).  Also is it worse when you have less fuel in tank (i.e. fill tank up).

-steve

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4 hours ago, geordie40 said:

Will do alan, looked at it the other day but dont know what im looking for. I still get a TPS error on the mems but its been changed. 

Do you know if disconnecting the battery has an effect on the ecu memory as my battery isolation switch is on the -ve so when i remove the key everything is dead

Try going for a short drive with MEMS logger running and make a note of the approx times into the journey when the misfire/hiccups occur. Then view the logfile in MEMSAnalyser to see if you can spot any anomalies on any sensors or graphs.  When I want to mark events while driving, I'll dip the clutch and do a high rev throttle blip so I can later find the point in time on the rpm graph.

Have you tried clearing the TPS fault code since you changed the TPS?  Or does the error keep coming back after being cleared?  If so try unplugging the TPS, spraying the terminals with contact cleaner, and replugging it a few times to clean the joints.

One other thing, when the engine is switched off, MEMS needs to hold the voltage supply open for up to 30 seconds in order to reset the stepper motor to closed position and save learned values to memory.  You say that when you turn off the key everything is dead - do you hear the stepper motor reset a few seconds after the engine stops?  If not I suspect your battery isolation switch might be interfering with normal MEMS shutdown.

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Good idea about dipping clutch and revving engine to mark the spot.

I reset the TPS but it comes back, will try cleaning contacts

Regarding the mems memory I can't be certain I hear it when I turn ignition off but don't normally isolate the battery straight away as fan is still running so I try and let it run for a while before turning the big "red" key.

I do usually hear a series of clicks when I turn ignition on though 

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2 hours ago, bullfist said:

 

In my experience on a tin-top, hiccup of power was caused by brief loss of fuel.  In my case, dirt in fuel tank.  In the SuperSpec you could check 12v to the fuel pump (wire a multi-meter across fuel pump and have it on the dashboard - watch when you get hiccup).  Also is it worse when you have less fuel in tank (i.e. fill tank up).

-steve

Thx steve someone mentioned maybe dirty fuel filter not sure where it is on a superspec.

I think the fuel pump is part of the whole fuel level sensor assembly in the tank (mk 5/6 escort I think)

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On my Superspec the fuel filter is a big metal canister mounted on the front of the pedal box. Not sure of its origins in the kit. And yes the pump is part of the level sensor in the Escort fuel tank

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8 hours ago, geordie40 said:

Will do alan, looked at it the other day but dont know what im looking for. I still get a TPS error on the mems but its been changed.

Do you know if disconnecting the battery has an effect on the ecu memory as my battery isolation switch is on the -ve so when i remove the key everything is dead

I told you in my post, check the MAP (Inlet pressure)  and see if it behaves as I described.  

Disconnecting the battery will kill some of the memory but the important stuff is held in non volatile memory so isn’t lost.

The fuel filter is where the original builder put it, there is no stock answer.

i really can’t help more until you run MEMSScan or MEMSLogger on a decent journey and post the log file.

 

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18 minutes ago, alanrichey said:

 

The fuel filter is where the original builder put it, there is no stock answer.

 

 

Do you know what it looks like, can't see anything that resembles a fuel filter as I know them (clear plastic with filter inside).

Will go on a decent run with memslogger running when weathers a bit better and send you the results Alan

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Andy and I both have the same filter but in different places.   Just follow the fuel lines through the tunnel and to the engine and you should find it.

As Andy said, the filter is NOT a clear plastic one, it is a metal canister about 6” long and 3” diameter.

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