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Engine loses power while driving


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#1 kevinr

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Posted 23 July 2008 - 09:48 PM

Hi,

While driving my disco 3.9 v8, I get moments where the engine loses power momentarily..well..It feels that way at least, The revs don't drop, but you get that lurch as if you change down a gear and release the clutch pedal.

As I say, it's only for a second, and doesn't happen all the time, and usually I am travelling at a constant speed, so I can't pu it down to a gear change or anything.

If it matters, I have a large hole in the rear silncer box on my exhaust, which I am waiting for craddocks t replace (they sent me the wrong part initially, despite using my vin number to locate the part :blink: )

Any help would be appreciated
1997 Dicovery I 3.9 V8i ES

#2 Rolly

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Posted 23 July 2008 - 10:17 PM

Hi Kev,
I've just gone through a similiar problem with my Tdi, 'twas the Hi-lift fuel pump on it's way out, though knowing nothing about the 3.9 V8 I can't say anything for certain.
Occam's Razor says that with all things being equal, the simplest answer is usually the correct one, so I'd be looking at fuel and spark - not enough of either of them will cause that power loss.
Aren't cars fun?
1996 Discovery Tdi Auto, 322,000km and still goin' strong
There is no Devil, That's just God when He's Drunk

#3 Rolly

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Posted 23 July 2008 - 11:07 PM

Me again Kev

Just got a call from my mechanic about my Tdi and wasn't the Hi-lift fuel pump causing that lurching problem, it was the wire leading to the fuel cut off switch. It had a dirty connection and kept turning the fuel off. Don't know if the V8 has one but it could be worth a look. Cheers.
1996 Discovery Tdi Auto, 322,000km and still goin' strong
There is no Devil, That's just God when He's Drunk

#4 kevinr

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Posted 25 July 2008 - 03:10 PM

Hi Rolly,

Thanks for your reply but, I don't think this has anything similar to it.

However, It seems the problem came to a head today, I went out to it this morning, to get some new spark plugs, and it wouldn't fire up.

I've replaced the Spark plugs, HT leads and the ignition coil of the ones they could get, one was upto 1995, and the next one was 98 onwards. Since mine is a 97, I went with the earlier one as it was similar in size to my existing one, and figured the newer one would be for a newer engine then mine.

Now I have it all fitted, I can turn the engine, but get no spark at all, so, here I am late for work and waiting for RAC to come out and diagnose the problem.

I've pretty much replaced the ignition system, and I know I'm getting fuel to the engine..so I'm outta ideas now.
1997 Dicovery I 3.9 V8i ES

#5 kevinr

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Posted 25 July 2008 - 10:28 PM

well, after much scratching of head, I called in the RAC. He's told me there is a signal problem from either the Distributor or the Amplifier.

So I guess my next step is to replace the amplifier first and see if that resolves the issue, if not, I guess I'll need to fork out for a new distributor :(

Anyone have any suggestions on how I can test either of these?
1997 Dicovery I 3.9 V8i ES

#6 FridgeFreezer

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Posted 25 July 2008 - 10:52 PM

The distributor itself is unlikely to need replacing, if you have an amplifier there are two types:
On the side of the dizzy (a small module), or bolted to the wing under the coil. Both suffer heat-related failures, so as they get hot they start to misfire. This then gets worse and worse until eventually you're going nowhere. The gubbins inside the dizzy is a magnetic pickup and a spiky wheel that induces a current in the pickup. There's not really much to go wrong there, I've never heard of one playing up (which must be some sort of record for a Lucas part?)

The on-the-dizzy type of amplifier are about £35, the under-the-coil type are about £eek but are easily replaced with a GM part for £25 that will give a decent spark and run silly racing coils.
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#7 First_Fleet

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Posted 25 July 2008 - 10:53 PM

If the amplifier is not presently remote mounted, it might be a good opportunity to do it now. It will keep it away from engine heat, which I am led to believe causes them to break down.

You will need the correct lead to do it, as well as the Amplifier. I have seen them in Rimmer Bros website in the Discovery catalogue.

Amplifier Module - electronic ignition;
2-Pin - (1) - NJL100060
3-Pin - (1) - STC1184
Remote - (1) - STC1856

GBP193 Oh my gawd! :blink:

#8 FridgeFreezer

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Posted 25 July 2008 - 10:57 PM

Found it - Rover V8 ignition upgrade for £25.

Worked well for me.
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#9 Rolly

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Posted 25 July 2008 - 10:58 PM

Hi Kev

Have a look at the "Definitive Alarm Spider Post" by BogMonster on page 5 of the Tech Archives

Could be just what you're looking for
1996 Discovery Tdi Auto, 322,000km and still goin' strong
There is no Devil, That's just God when He's Drunk

#10 kevinr

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Posted 26 July 2008 - 04:56 AM

my amp is located just behind the coil at the front of the enine bay, behind the lights. I'll be straight onto this today as soon as I finish my breakfast shift...I sooooo miss my landrover right now :(
1997 Dicovery I 3.9 V8i ES

#11 kevinr

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Posted 26 July 2008 - 10:57 PM

that post looks promising rolly..thanks :)

I had an auto eletricion out to me today, before he arrived, i had managed to find that I had spark, but my problem was now fuel..after injecting a few ml's of petrol directly into the cylinders, replacing the spark plugs and cranking it..she started to fire up!!..so, after much poking around, I found that the plugs were dry, and the engine would try to fire if I injected fuel directly..ergo...fuel injectors or pump to blame.

Once the electrician arrived, he checked the pump, and the pressure, and said that it was feeding fuel to the injector rails, however, the injectors were not working...which he said was highly unlikey as to have all 8 injectors fail at the same time was unheard of.

We found the inertia switch..which had depressed...but this did not solve the problem when pressed in again :(, now..some people may remember a post I made weeks ago, about a wire running from my ignition stright through to the ignition coil..turns out..this is a bypass, and provides an ignition live circuit directly to the coil....so...given our post rolly..it may actually be the solution to my problem..which this electrician was unable to solve..but hat off to the guy..his protocol (as he was roadside recovery) is 25 mins, then recover...he spent near 3 hours helping me, so no complaints there, but he did say I would need a landrover specialist as he couldn't figure out why the injectors refused to fire..his best guess was eitehr the ECU was on it's way out, or the crankshaft sensor was kaput..any ideas where this is??? Hid diagnostic machne wouldn't communicate with my ECU...which led him to the conclusion of the sensor...but, what do I have to lose? 3 hours checking this little box of tricks??..pfft..if it works, then I'm happy, as it saves me another call out fee
1997 Dicovery I 3.9 V8i ES

#12 6cyltdi

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Posted 26 July 2008 - 11:28 PM

Right, I have the 97' 3.9 disco too, I also had trouble with exhaust and just modified the one I got.... All the service items I have needed for it inc drive belt have been for the 4.0 model....? see if this corresponds to your car too...

I would change the fuel filter, clean the pump and blow back your fuel lines... Fill the tank with fuel and hopefully problem solved...

Had a similar problem with my 3.9 hybrid, dyeing out under load twas the fuel... ended up binning the tank ( a mingin home made one changed filter and cleaned lines.... problem solved..

Hope this helps, cheers

Daniel

#13 First_Fleet

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Posted 27 July 2008 - 12:47 AM

Sounds like you may be on the right track now. :rolleyes:

Harking back to the Ignition Amplifier 'overheating' problems.

I recall a couple of years ago after reading similar posts somewhere, inspecting mine & finding that the area around mine was covered in a thick coating of oily gunk (rocker cover leak I think & one of those sneaky type leaks).

I pondered the question of how many problem vehicles with the Amp "problem" were in actual fact vehicles running with gunk covering the Amp & being heat sensitive, would they have benefited by a good regular degrease?

I also recall reading, that a good test if it starts this cutting out business, was to empty the contents of a cold bottle of water over it, or wrap it a cold wet cloth. (How you would get a cloth in there easily beggars belief, but there you are.) Let it sit for a couple of minutes & restart.

Anyway, I now make it a practice of keeping that area clean & free of grease. The rest of the engine is kept clean but that area gets more attention due to it's location & possible reduced cooling air flow.

Will it stop it happening? I don't know, but it seems to me to be a feasible explanation & an easy routine fix.

#14 First_Fleet

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Posted 27 July 2008 - 03:21 AM

Edit time seems to be expired.

How can I tell how many pins ie. 2 or 3 my Amp. has got without removing it?

Is it in the number of cables in the adjacent loom or what? Colours?
It's an MA 0827 ....... prefix. Build Date 4/94

#15 kevinr

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Posted 27 July 2008 - 05:48 AM

Edit time seems to be expired.

How can I tell how many pins ie. 2 or 3 my Amp. has got without removing it?

Is it in the number of cables in the adjacent loom or what? Colours?
It's an MA 0827 ....... prefix. Build Date 4/94


I wouldn't know mate. When I replaced mine, I never looked to be honest, I just asked the motor factor for an amp and took the one he gave me, there's no real markings on it.

Mine had 5, spread between 2 clips, the bottom one could be removed with some difficulty and much swearing, while still in place, but the rear clip actually feeds through the earthing place and is essentiually locked onto the amp itself.
1997 Dicovery I 3.9 V8i ES

#16 First_Fleet

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Posted 27 July 2008 - 09:48 AM

I was looking for something else & came upon this. Sounded familiar & it may help you.



http://en.allexperts...ine-problem.htm

#17 FridgeFreezer

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Posted 27 July 2008 - 12:57 PM

Having spark is not the best indicator, it can be too irregular or too weak to actually run the engine. You've got fuel to the injectors, an easy check of fuel pressure / pump function is to splice a clear inline fuel filter into the return line (the one that comes from the regulator), you should see a good stream of fuel returning to the tank through it. If it's not, either the regulator is stuck closed or the pump isn't making enough pressure. A slow trickle could be a blocked filter.

However, the injectors failing to fire seems to be more the issue. Your mechanic is right, injectors very rarely fail, and he's sort of on the right track, although the Flapper & Hotwire EFI doesn't have a crank sensor. They both take their tach signal (engine turning) from the ignition amplifier or coil -ve terminal. On flapper it's a white wire with a black trace, not sure about hotwire. If the ECU doesn't see a stream of pulses from the ignition amp, it assumes the engine isn't turning and therefore doesn't inject any fuel.
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#18 kevinr

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Posted 27 July 2008 - 03:28 PM

although the Flapper & Hotwire EFI doesn't have a crank sensor.


How do I tell which mine is?

I do have a wire disconnected from the coil which is white with a black trace, and connects to the positive terminal..however, the wire from my ignition wire is connected to that
1997 Dicovery I 3.9 V8i ES

#19 kevinr

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Posted 27 July 2008 - 06:24 PM

well, I removed the alarm spider..and sure enough...dry solder joints!. I re-soldered them..even applied that mod..but nothing...still dead as a doorenail...guess I'm just gonna have to wait and pay for this landrover specialist auto electrician now :(

All I can think of as a possible cause now is my ECU
1997 Dicovery I 3.9 V8i ES

#20 kevinr

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Posted 28 July 2008 - 08:21 PM

It's Fixed!!!!

The landrover guy turned up ( a little late for me to order new parts for next day delivery if needed) and hooked his diagnostic computer up..after failing to read the engine....turns out my car has a seperate port for that, he traced to problem to an earthing fault, which eventually led to the ECU (Oh great!)

He was just packing up after removing the ecu for testing in another vehicle, when we both looked over the previous work I had done, then he noticed something was not quite right with the wiring on the ignition coil.

It turns out, when the RAC mechanic was testing the ignition system, he had reconnected the earth wires for the injectors incorrectly..so, this guy plugged the ECU back in, swapped the wiring over to what he thought it should be and she fired instantly!!!

So, the original problem was indeed the amplifier, but the inadvertant switching of wires caused an earth fault, which was easily fixed....what a f**k about, but kudos to this guy for spotting it..despit his machines telling him otherwise!!
1997 Dicovery I 3.9 V8i ES




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