Engine Hunting

[airwolf929]

Hi, I am new to Elans and now have a 92 SE. When warm the engine hunts just like a diesel lorry at rest! Also, at low speeds like rounding a roundabout or following slow traffic the engine misses badly and occasionally will stall. Always restarts ok but starts hunting again. Once rpm is above c.2000 all is smooth and engine temp stays in first quarter generally.

I did the paper clip test and got no fault found. Now, I am a retired engineer (electrical) and NFF has always caused grief when you KNOW there is a fault. My engine light spells 12 for ages and does not show any other code. Can this be because the ECU is faulty and is not logging faults, or is there somewhere I can look for enlightenment? Replacing CAS and CTS have no effect whatsoever.

Any comments welcome!!!

[GeoffSmith]

Welcome to LEC Mike.

It would be worth checking for air leaks first. The MAP and MAF sensors may be giving erroneous output that isn't sufficient to throw up an error but might be visible on an ElanScan run.

[tweetdriver63]

The 12 code isn't a fault. It's just indicating you're in the diagnostic mode. It will display the 12 code three times, then any fault codes (three times each), then the 12 code again to show you've gone through all of them.

[airwolf929]

Welcome to LEC Mike.

It would be worth checking for air leaks first. The MAP and MAF sensors may be giving erroneous output that isn't sufficient to throw up an error but might be visible on an ElanScan run.

Thanks Geof (!) MAF - did you mean MAT?

[GeoffSmith]

Yep - FFT (Fat Finger Trouble).

[Monty]

Check ignition leads haven`t worked loose ie at the sparkplug & coil end
Check to make sure the spark plugs haven`t come loose
Check sparkplug condition
Check ignition leads condition

If they check out then it could be a faulty coil/s

[airwolf929]

Check ignition leads haven't worked loose ie at the sparkplug & coil end
Check to make sure the spark plugs haven't come loose
Check sparkplug condition
Check ignition leads condition

If they check out then it could be a faulty coil/s

Thanks to all for your pointers. I have checked what I can and everything seems OK. Plugs, leads and sparks are fine. So, I have taken the car to a Lotus dealer/engineer who has done initial checks with the Tech 1 device. I left him scratching his head and muttering "in 38 years working on Lotus cars I've never seen the like!!!!" Anyway, I've left the car with him for a few days and will have to see what turns up!!! If it is the ECM

[GeoffSmith]

If you'd used ElanScan, you could have posted the results up here and we could have said "never seen anything like it" for free!

[Doug]

you could put the car into "service mode" and that would lock out the sensors and then you should have a steady idle -- if not that would be a problem . . .

[airwolf929]

If you'd used ElanScan, you could have posted the results up here and we could have said "never seen anything like it" for free!

Only one problem with that Geof (with one f), I only had a paper clip! I might make up an Elanscan sometime, but too late for this one.

[airwolf929]

you could put the car into "service mode" and that would lock out the sensors and then you should have a steady idle -- if not that would be a problem . . .

Thanks Doug, pardon my ignorance but would "service mode" have anything to do with paper clips? If so, would the engine need to be running before, or after the short is applied?

[GeoffSmith]

you could put the car into "service mode" and that would lock out the sensors and then you should have a steady idle -- if not that would be a problem . . .

Thanks Doug, pardon my ignorance but would "service mode" have anything to do with paper clips? If so, would the engine need to be running before, or after the short is applied?

Inserting the paper clip when the engine is running disables sensors and opens the IAC valve - there is quite a bit on the Wiki and it has a good search facility.

[airwolf929]

you could put the car into "service mode" and that would lock out the sensors and then you should have a steady idle -- if not that would be a problem . . .

Thanks Doug, pardon my ignorance but would "service mode" have anything to do with paper clips? If so, would the engine need to be running before, or after the short is applied?

Inserting the paper clip when the engine is running disables sensors and opens the IAC valve - there is quite a bit on the Wiki and it has a good search facility.

Cheers Geof, I haven't come to terms with Wiki yet, but will go there and play a while.

[airwolf929]

Well, the latest is that the Lotus Engineers (Fibreglass Services @ Walberton) have had the car for a month now. I've been in Ireland for most of this. On my return I phoned for an update - they've changed everything but the kitchen sink (which they couldn't find), including the ECM (I have bought one from SW Lotus for <200 squids). The problem remains!!! Previous owner for 6 years says it was doing this when he bought it from a reputable Lotus dealer! He didn't tell me that when I bought it from him! It passes its MOT on emissions because when the engine is hunting it is running lean.

I get the car back next week, after the bonk holiday, and will try the Service Mode paper clip thingy and/or try my new ECM. I am trying real hard to be optimistic about this, but I already believe it will be no different!! Watch this space.....

[Doc Fizzix]

For what it is worth, it sounds like the secondaries may be stuck open. The cause of the secondaries being stuck is normally a faulty switch or a vacuum leek. If the secondaries do not close at low RPMs then the car hunts a lot. I had this problem when I rebuilt my motor and some how knocked the vacuum line off the secondaries switch OR I had disconnected the switch (it was one of the two I just can't remember which one - man I am getting old) Anyways, you will get no code errors and it is almost impossible to find unless you have experienced it before.

The quick test, with the car running, with the hood open, and standing in front of the car look through the intake plume where the injectors are attached to the injector housing. In the middle of the injector housing you should see the secondaries vacuum actuator that opens and closes the secondaries, with the engine at an idle the valve should be closed, rev the motor up using the throttle on the intake plume and the valve should open, watch to see if the actuator moves up and down as you change the rpms of the motor. If the actuator does not move up and down you have a problem with the secondary system, check for a vacuum leak or a bad switch

Give it a try, it may be the problem

[airwolf929]

Hi Doc,

Thanks for that. I collect my car from the mystified Lotus Engineers later today - they have not seen the like in 38 years of working on Lotus cars! I will follow what you say tomorrow, Thursday 28th and will let you know what transpires. It sounds interesting!!! I shall report back as soon as I have done what you say.

I shall have everything crossed that will cross

[airwolf929]

For what it is worth, it sounds like the secondaries may be stuck open. The cause of the secondaries being stuck is normally a faulty switch or a vacuum leek. If the secondaries do not close at low RPMs then the car hunts a lot. I had this problem when I rebuilt my motor and some how knocked the vacuum line off the secondaries switch OR I had disconnected the switch (it was one of the two I just can't remember which one - man I am getting old) Anyways, you will get no code errors and it is almost impossible to find unless you have experienced it before.

The quick test, with the car running, with the hood open, and standing in front of the car look through the intake plume where the injectors are attached to the injector housing. In the middle of the injector housing you should see the secondaries vacuum actuator that opens and closes the secondaries, with the engine at an idle the valve should be closed, rev the motor up using the throttle on the intake plume and the valve should open, watch to see if the actuator moves up and down as you change the rpms of the motor. If the actuator does not move up and down you have a problem with the secondary system, check for a vacuum leak or a bad switch

Give it a try, it may be the problem

Well, I took your comments with me to the Lotus Engineers who carried out your suggestions - it all seems to work OK!! However, the car now will not accelerate properly, there is no 'urge' and it is difficult to get it up to 40mph without the orchestral accompaniment of backfires from the exhaust and from under the hood. The engine light keeps coming on (I will do the paperclip check to see what it says), and the engine is running very hot (in the 3rd quarter most of the time). So, the hunting is improved, but now the car is virtually undriveable, so it's going back next week.........!! Great thanks for your help though Doc!

[RayD]

This is a sad tale Mike,

Presumably after a month its cost a fair amount to get nowhere.

Would it be worth preparing a checklist of all the things it might be, and get the garage to tick off all the ones they’ve eliminated, and how?

Starting with...

Compression test
Spark plugs
HT Leads
Coils
Fuel pressure

and so on

Ray

[Enright]

It sounds very suspicious - they very rarely run that hot - usually it's around the 1/8 mark.
If the thermostat fails in the closed position you get a cold reading because the sensor is on the opposite side, and if it fails open then the engine just runs cool.
To be getting to such a temperature on a regular basis it almost sounds like the cooling system has been blocked.
That paperclip test will make for interesting reading.

[Doc Fizzix]

It sounds very suspicious - they very rarely run that hot - usually it's around the 1/8 mark.
If the thermostat fails in the closed position you get a cold reading because the sensor is on the opposite side, and if it fails open then the engine just runs cool.
To be getting to such a temperature on a regular basis it almost sounds like the cooling system has been blocked.
That paperclip test will make for interesting reading.

Hmmm...

Have you replaced the temperature sensor? I still say to check to make sure the secondaries are working first, that is what the symptoms sound like but a malfunctioning temperature sensor can cause a list of strange behavior