director_steve

director_steve

Active Member
I've posted about this a couple of times so far, but i'm still desperate for help....apologies.

My 3.9v8 (97 Disc V8 with ECU rewired so it runs without CAT or Lambdas- 105k miles) defender has a bit of a temperamental attitude.

Essentially, she runs quite rough- low on power, backfiring etc most of the time. It's really bad when the engine is cold, but never fully goes away. BUT, when she's running rough, the idle is always really smooth.

HOWEVER, if i unplug the AFM she runs really nicely- still slightly lumpy for the first 2mins, then runs absolutely fine BUT the idle (only when running on petrol- not gas) fluctuates up and down.

I have replaced the AFM- no luck. I have also replaced the coolant temp sensor for the ECU- still no luck.
I have also inspected the wiring loom, cleaned up the connections, and found no green copper wires (so no water ingress).

Aside from replacing the AFM AGAIN, or replacing the ECU and having it rewired AGAIN, i'm at a loss. :doh::doh::doh:

HELP?
 
Er... i can't.

All i know is what i was told by the garage i got to do the original install: that in order for the engine to run without CAT and Lambdas the ECU had to be 'rewired' (although i'm not sure that's the word they used- it was a while ago)

The engine itself was built bu a guy who specialises in custom ECUs for racecars, and ran without any fault for 5000miles. When the fault occurred it started more intermittently, now it's every time it's driven.
 
To clarify that's probably my biggest problem with this- i know next to nowt about the engine and install requirements as i didn't do the work myself. Instead i gave a garage ALL MY MONEY to do it. :hurt:
 
well...

might i suggest you cant have ecu rewired to not have the lamdas...not totally sure on this but ecu neds to know if runing rich or weak to work....so i suggest this would be my first port of call...i would think ecu going into limp mode without lamdas..and hense never work as it should..
ie you cant just put a resistor in to fool ecu..they dont work that way..

AND besides..why the hell would you not want lamdas??cats yes, but lamdas???they are the heart of the ecu's abilty to get fueling correct...(apart from map)
 
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Hmmm.

But in that case it would have been running rough all the time? The problem only appeared after 5000miles.

I'll call the garage and see if they can shed any light- i haven't bothered them for a while.
 
ahh..sorry misunderstood....so same garage did original install...so why then cant the same guru sort it???

and why you not want lamdas?????
 
zen said:
ahh..sorry misunderstood....so same garage did original install...so why then cant the same guru sort it???

and why you not want lamdas?????
Click to expand...

The original garage is a good 250miles away from me now (change of job etc etc) and i can't afford to have it looked at professionally (Totally broke!), with southern garage prices!

I can't remember the reasoning behind lambdas, but i think it was something to do with getting the exhaust to fit properly and to keep costs down. The conversion was started 18months before it was finished, because my marriage failed and i couldn't afford to get the old truck back. The garage gave me a hefty discount because they felt sorry for me- so i'm reluctant to push them for more freebies!
 
Are you running a standard ECU or is it a custom ECU? If it is a standard ECU it sounds like the ecu is not getting an input somewhere and is going in to limp mode which is a basic fuel map. By having your foot to the floor the engine runs better because it is being given lots of fuel to burn.

Again assuming a standard injection system I would start by checking all the inputs to the ecu: coolant temperature thermistor, throttle potentiometer, fuel thermistor, air flow meter (CO trim, air flow signal) you say you don't have gats so we don't need to worry about that.

If you do a search you will find how to check/test the efi with a multimeter.
Once you have checked over the efi side, look at ignition. Assuming the ignition system is standard there should be no issues there making the right hecks, again do a search.

The iffy bit is what if everything checks out? Well it is not unknown for an ecu to be the fault - get hold of a known good ecu and swap it out and see if that sorts it in which case you'll know it was the ECU.
 
Thanks Kev.

The ECU is standard- but, like i say, i believe it was altered to run without Lambdas (although i don't know much about that). The injection and ignition is also completely standard. Only change is the air-filter.

Forgot to mention i also replaced the Throttle Pot.

Think i'm best to start with the fuel thermistor (if i can find it).

Steve
 
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If it is a standard 14CUX ECU then the only thing needed to run without cats is a change of tune select resistor, it should have 470ohm IIRC.

You can re-set the ecu by disconnecting it or by disconnecting the battery. Do a search for how to check the throttle pot, air flow meter and both coolant and fuel thermistors - I am pretty sure the appropriate tests have been posted a number of times.

In your first post, what you describe issues that could be the coolant thermistor - check the resistance when cold or in the alternative, remove the plug from the thermistor and bridge it with a paper clip - the ecu will think the engine is hot and see how that goes.

The rough idle is potentially down to a combination of factors - ignition timing and fuelling. I would recommend removing the plenum and ram housing and giving it all a really good clean, then check and set the throttle disc (I've posted on this before so do a search). You will need to set the base idle after but that is quite easy. Check the ignition timing, set it for petrol then go from there - you said something about being on gas? in which case the timing will be advanced
 
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Thanks again.

Think my multimeter has gone walkabout at work, so i'll find it and have a look at this tomorrow. If running without cats is just a change of tune select resistor, does that mean i could swap out the old ECU for another without having to modify the new one?

I took it for a drive and had a play this afternoon. It ran absolutely faultlessly for about half an hour in a mixture of urban and country roads, then threw a wobbly and i could only get it to move by putting my foot to the floor. I tried disconnecting various sensors, but it made very little difference. I disconnected, then reconnected the coolant temperature sensor (thermistor) with the engine running which initially cured the rough running, but 20mins later it was back.

Disconnecting the fuel thermistor made absolutely no difference- also i tried to replace it before but couldn't find a stockist anywhere.

It's definitely over-fueling when the AFM is disconnected- fairly strong smell of fuel. The idle is only rough when this is the case as well.

I'll hopefully track down my multimeter and report back in a few days. I've found a bunch of useful info on britishv8.org, which should help. I plan to check each sensor in turn, make a note of their readings, then check again at the ECU end, to try and rule out poor wiring. I think i've found the normal Ohm readings for each sensor so i'll go from there.

It's getting to the stage where i can't affford to keep her...I just hope it turns out to be something i can diagnose myself, or i'll have to find a new home for her. After 5 years of love and about 12 grand it'd be pretty gutting though :hurt:

Anyway. Thanks again. I'll report back soon.

Steve
 
Yes you should be able to swap ECU with another 14CUX.

From what you have said it sounds like he ecu has been in limp mode which causes it to run very rich, unplugging sensors won't help if this is the case because every time you unplug a sensor it will go in to limp mode. Reset the ecu, clean the plenum etc and start from there.

Anyway, a few tests with a meter and you'll hopefully be sorted. One other thing though, assuming this is a conversion, how does the ecu get its speed sensor input? Might be one to check in to - no speed sensor then no idle stabilisation and ecu will go in to limp mode or at least that is what happens on a RRC.
 
there is another option...about 400 quid and some time...but a megasquirt ecu...one can buy plug and play or hard wire it in..
plenty plenty v8 rovers done..soo much info...

here...ExtraEFI.co.uk | Home is where i got mine from to run supercharged v8 quad cam...he is very helpful and cheapest about..

i know you skint, join the club!..but compared to paying garage to sort yours out might work out much cheaper in long run..AND better mpg and hp to boot..
 
zen said:
there is another option...about 400 quid and some time...but a megasquirt ecu...one can buy plug and play or hard wire it in..
plenty plenty v8 rovers done..soo much info...

here...ExtraEFI.co.uk | Home is where i got mine from to run supercharged v8 quad cam...he is very helpful and cheapest about..

i know you skint, join the club!..but compared to paying garage to sort yours out might work out much cheaper in long run..AND better mpg and hp to boot..
Click to expand...

Sorry to the op but, zen how is his stuff and the ms2 direct coil fire ecu? as I heard the can have issues hence a lot of guys going with ms1 and edis.
 
i run ms3x..that uses 5v to trigger coil amps. though it also has provision for direct coil fire using wasted spark, though i use full sequential.
one orders ms1/2 with provision for what ever you require...
 
Yeah, i'd been looking jealously at Megasquirt. Think i might invest in the future.

In the mean time i check all the sensors with a multimeter and they all seem to be working spot on, but i think i may have found a slightly dodgy connection- to the Fuel Thermistor. I've made a temporary fix to keep it in place, and went for a 30 mile drive with no issues whatsoever...just going to keep using it and see if it comes back. In the mean time is there anywhere i can buy replacement connectors (the squareish ones), or even replacement retaining clips? I've done a search but no luck...

Thanks again all!

S
 
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