I couldn't start my 98 disco(quick repetitive clicks). Scan gauge was showing about 10V. Used the booster cables to start. Car started ok but Idle was rough.

I put a new battery in (used my marine battery) when I got home since I had to leave again and it did not start as well as usual. The engine revs up freely but then idles roughly. I got a P1316 code, cleared it and it did not come back but the idling is still irregular.

Is it possible that some sensor got damaged? Or may it just be a coincidence and two remote problems?

Thanks for any hint.

 

First make sure you have enough voltage in your battery. The ECU supplies Positive power and ground to all the sensors. In most instances the ECU sends out one positive and one negative wire to be branched off of to numerous sensors. If one sensor in this chain is acting up, it could definitly effect the others. A bad sensor will either create resistance or nothing at all. Depends on the severety of the damage to the component. I would start with the IACV idle air control valve. This valve consists of two really thin wired coils which actuate it in and out. Pull the two bolts and leave it connected to the wired plug. Pull the IACV out of the chamber and place it where you can see it through the drivers seat. Turn the ignition to the second position. The IACV should move in and then out again. No movement is bad. Also there is a spring on the IACV shaft. Unscrew the shaft and remove the spring. Now try the test again with the key in the second spot. Of the two coils in the IACV, one pushes out while the other pulls in. Removing the spring will let you know for sure if a coil is bad. Do not forget to put the spring back on the shaft and screw the shaft back in the same amount of turns you took it off.

 

Makes lots of sense. I runs much better when warmed up and pulls well under load. I will check this tomorrow after work.

Thanks

 

Haven't had a chance to do the test tonight but...the problems seems to be gone!?
To be continued...

 

Holy Crap that is some scary advice....... one positive and one negative wire supplying multiple sensors? really? engine sensors being knocked out by one another??? really? I just want to make sure I understand what you are saying ... I would appreciate it if you would quote the page number and specific diagrams where you find that to be the case... i"ll give you a clue, section A. Are you suggesting that the MAF and TPS and ECT can "could definitly effect the others" if one of them is faulty?

Iacv not a sensor by the way...

And DO NOT just uncrew the cone shaft from the IACV motor body... it needs to be fully expanded under its own power before you can safely unscrew it. almost to the point where it pops out by itself.

 

Batiscan...Also, if your battery is down to 10V it would be best not to jump it and run the engine. That could burn the charge circuit in your alternator. Better to charge it overnight with an external charger.

 

Cosmic88 check ECU Connection C (Large Red ECU Connection), Pin #12 Red/Black striped wire. Supplies ground to the TPS, ECT, Fuel Rail (EFT), MAF, IAT and Alternator. This wire has a bare connection. A connection midway which ties in multiple sensors on one lead. This connection does not have insulation and can disconnect or corrode. This information is derived directly from the parts itself. Spare ECU, spare wire harness that I have directly followed each and every wire to and from destination. The injectors wire Brown/Orange has the same setup. All connected and branched off of one lead. It too has a bare connection with no insulation. One or more wires at these connections can corrode or loose continuity, causing failure. The multiple wires are connected by a crimped piece of copper over bare wire. Now you have it.

 

I am very interested in the specific construction of the wire harnesses as I have found that to be one of the manufacturing weaknesses in our beloved Discoveries.

Detailed photos of the items identified by our fellow members would help to document these weaknesses and help us all in improving any such potential problem areas.

LRD, got your camera handy?

I am currently trying to resolve some similar issues on my 97. I finally got the new RAVE download done and started reading up on the Electrical Troubleshooting Manual. It is much better than what was in the RAVE CD I purchased four years ago when I first bought my Discovery.

The way LR made only 1 harness to fit all vehicles, there are a lot of unused wores and connector throughout the vehicles. The inline sploces they used are not well protected and the overwrap they used tends to break down with age and exposure to it's envirioment. I hate the wiring fiasco they built as a simple manufacturing technique for one standard harness to accomodate all possible vehicle options. Their routing and general cheap manufacturing techniques is a major weak point in these otherwise hardy vehicles. They could have built a much more robust set of
sub-harnesses that would have lasted longer and performed better for the users instead of the sorry cluster**** that we all have to deal with.

Of we all apply our group knowledge constructively we can identify and resolve these inherent weaknesses and continually improve these design flaws like creative individuals.

How about that for "REDNECK RE-ENGINEERING". AFTER ALL I AM A FORMER US NAVY AVIATION ELECTRICIAN AND CRUISE MISSILE ELECTRICAL MANUFACTURING AND RELIABILITY ENGINEER WITH 20 PLUS YEARS MANUFACTURING SUPPORT EXPERIENCE ON WIRE HARNESSES.

HAPPY TRAILS GUYS.

 

Do you happen to know the year and model your spare harness and ECM came from?

I ask because the NAS 1998 D1 SFI V-8 ETM completely contradicts the details you just gave.

The connector you reference is C1017 (36-R) - pin pos. #12 is for the Right Knock Sensor (yellow wire).

The RB (red w/ black trace) wires you referenced as common ground leads are spliced together at S150 and then lead to pin #36 of C1017. Were this ground bad those sensors would ALL be effected...is that what you meant to say? for reference the RB (ECM grounds) are pin positions #10, #32 and #36.

One of the sensors being faulty will not effect the others as you stated. In fact the power supply wires to each individual sensor (13, 14, 35, 4, 15, etc...) are all seperate and again, will not effect each of the other sensors.

The injectors are (as we know) not sensors and operate differently. They do have a common positive supply. They are operated by the ECM by signaling for individual injector grounding... this ground signal then actuates the individual injectors.

 

Cosmo, I love your detailed knowledge on these beasts.

Is the GEMS engine considered to be SFI (Sequential Fuel Injection)?

I am still learning some of the finite differences in these vehicles and getting accustomed to the documentation. Boy what a chore these can be!

Had to get accustomed to reading and thinking again. That is hard for an Old Redneck like me. Can you use more pictures please?