1995 Disco 1

My vehicle is having some rough idle and dying problems. Here are the symptoms:
-Sometimes tough to start, have to give it quite a bit of gas before it catches
-Idles rough
-Will stall when I slow down at a light or to turn
-Usually generates a check engine light after a few stalls.
-Here's the interesting thing: it does much better in all of these areas when the outside air temperature is warm (80 degrees F). The outside air temp seems to affect things more than the engine being warm or cold. On a warm day I might go all day without a single problem. Today it was about 60 degrees and it did not want to behave.

It has new plugs and wires, so I don't think that's the problem.
I don't believe it is the MAF sensor.

Could it be the throttle or stepper motor? I don't know when the throttle was last cleaned.
O2 sensors?
I have an exhaust leak upstream from the muffler a little. Could this be due to an exhaust leak or maybe a bad cat?

I feel like it should be something with the supply air since the outside air temperature has such a big effect, but I dunno.

I'll post the computer codes when I get them read, but it's OBD1, so I think I'm going to have to pay a shop to pull the codes.

(PS The octane boosters seem to help a little, but they were not the miracle cure that I once thought they were.)

ANY IDEAS?!?

 

obd1 go to advanced auto parts they will lend you a diag tool, one thing some of the d1s had trouble with rust in the rails (fuel) and it plugs the injecters setting a lean trim code i forget the p code

 

do you get a lot of black smoke from the exhaust? no power, sounds like a MAF sensor to me. I had a similar problem I didn't want change it out. but when I did the problems went away. just a guess.
Gtagg

 

An OBD1 will still give code numbers which you really need before throwing parts at your truck. Here is something hat will help you.
Mike


Engine Fault Codes
Note: This information is for the 4.0 liter V-8 OBD I (On Board Diagnostics, phase I) Petrol engine that is found in the US. The information may hold for other markets and engines, but we cannot confirm this. It may also be true for Defenders and Range Rovers with the same engine. Again we don't know.

NAS Discoveries have a digital readout for diagnostics. It is a black plastic box measuring approximately 1" x 2.5" x 3" with a red LED readout. It is found under the passenger seat facing backwards. It may be unclipped and moved so that the driver can see it.

This doesn't give nearly as detailed readout at the official test box, but it's better than nothing.

Fault Codes
Jump directly to the fault code:
02 12 14 17 18 19 21 23 25 28 29 34 36 40 44 45 48 50 58 59 68 69 88

General:

* The fault codes are given in order of priority. If more than fault exists, you have to clear the display before the next fault code can be displayed.
* Fault code 02 meas that the ECU has just been reconnected. Switch on the ignition to clear the display.

Clearing the display

1. Switch ignition on.
2. Disconnect serial link mating plug, wait 5 seconds, then reconnect.
3. Switch ignition off, wait for main relay to drop out.
4. Switch ignition on. The display should now be reset. If there are other faults, the next one will be displayed. Otherwise the display will be black
5. If there is more than one fault repeat steps 1 to 4, to clear each fault until the display is blank.

No LED's are on:

Good news; nothing is wrong. Either that or Mr. Lucas has struck and either the LEDs are burned out or the display isn't getting any power.



Code 29 - ECU memory check

If detected all other faults are unreliable and must be ignored.
Procedure:
1. leave battery connected
2. switch ignition off
3. wait for approximately 5 seconds
4. disconnect ECU plug.
5. reconnect ECU plug
6. switch ignition on and check display unit.
If fault code 29 is detected again, swap out the ECU for another one and retest.


Code 44 - Lambda sensor A - left bank
Code 45 - Lambda sensor B - right bank

If one of these fault codes is displayed check the wiring to that particular lambda sensor.

If both codes are displayed, the voltage supply to the heater coils of the sensors must be checked. Refer to test 26, continuity test procedure.


Code 25 - Ignition misfire

This code indicates that an ignition system misfire has been detected. Codes 40 or 50 indicate on which bank the misfire has occurred.


Code 40 - Misfire bank A - left bank
Code 50 - Misfire bank B - right bank

If both codes are displayed, check the following components common to both banks:
Distributor cap
Rotor arm
Coil
Electrical connections
Pick-up (air gap)
Amplifier
Injectors (if code 34 or 36 is displayed)
If either fault code 40 or 50 is displayed check components applicable to the particular bank that the misfire has occurred on.
Spark plugs
HT leads
Distributor cap
Injectors - if code 34 bank A or 36 bank B displayed


Code 12 - Airflow meter
Refer to test 19, continuity test procedure.

Code 21 - fuel tune select

Identifies that the tune select resistor is open circuit- refer to tune select resistor test.


Code 34 - Injector bank A

The display will indicate if the injector(s) are causing the engine to run rich or lean.

If the bank is running rich, check for - faulty injector wiring and connectors, stuck open injectors.

If the bank is running lean, check for - faulty injector wiring and connectors, blocked injectors.


Code 36 - Injector bank B
As code 34, except relevant to bank A injectors.

Code 14 - Coolant thermistor
Refer to test 14, continuity test procedure.

Code 17 - Throttle potentiometer
Refer to test 17, continuity test procedure.

Code 18 - Throttle potentiometer input high/airflow meter low
refer to tests 17, 18, and 19 of the continuity test procedure.

Code 19 - Throttle potentiometer input low/airflow meter high
refer to tests 17, 18, and 19 of the continuity test procedure.

Code 88 - Purge valve leak
refer to test 9 and 10 of the continuity test procedure.

Code 28 - Air leak

check for air leaks in the following areas:
o Hose, air flow meter to plenum
o Breather system hoses to plenum
o Brake servo hose
o Vacuum reservoir hose (fresh air solenoid)
o Distributor vacuum advance
o Hose, purge valve to plenum
o Injector seals
o Joint - bypass air valve to plenum plenum chamber to ram housing ram housing to inlet manifold inlet manifold to cylinder head bypass air valve hose


Code 23 - Fuel supply
check fuel system pressure, test 20 of continuity test procedure.

Code 48 - Stepper motor

check base idle speed- see setting procedure. Refer to tests 15 and 16 of continuity test procedure. Check road speed sensor- refer to test 25 of continuity test procedure.


Code 68 - Road speed sensor
refer to test 25 of continuity test procedure.

Code 69 Gearswitch
refer to test 24 of continuity test procedure.

Code 58 Group faults 23/28

This indicates that a fault has been registered that is caused by the fuel supply or an air leak but the exact fault cannot be identified. Check all items outlined under codes 23 and 28.


Code 59 Fuel thermistor
Refer to test 13 of the continuity test procedure.


Copyright Dixon Kenner, 1995-2006. Last modified March 15, 2005.
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The (primary) code on the LED display was 48, which, according to Mike, is a stepper motor. This makes a lot of sense to me since the problems seem to happen when the truck is entering idle.

Two things:
1. How long do I have to wait (in reading the OBD1 codes) for main relay to drop out? I can't seem to get past this code to see if there are any others?
2. Anyone replaced one of these? It seems like it should be pretty simple. The dealer wants ~$225 for the part. Any recommendations for an alternate source?

Thanks.

 

I tried to clean and lubricate the stepper motor, and that seems to have helped somewhat, but it still seems sticky. It now will idle a little high on occassion, and it is still throwing a 48 CEL code. Is there a good way to give the thing a more thorough cleaning?

I've also heard that there is a GM part that fits the 95's. Anyone know the part number or what vehicle it is for?

Thanks.