Hey folks,

I have a 97 Disco that I recently did a major service on, Heads, New Crower Cam/Lifters, oil pump, timing chain etc etc... Tore it down in the vehicle to the crank, block & pistons. Put it all back together with a new fuel pump, plugs, wires, fuel filter... Ran NICE! for the past month. Pulled into the driveway after work and notice the idle increased right before shutoff.

Started it the next day and drove for a while and it started bucking, popping back through the intake and sounded like a timing/electrical issue. So I plugged a cheapo OBDII reader into it and got 0360 code a 0541 and a 0340 code. So I pulled the Cam sensor and it looked pretty beat up so I replaced it and checked the wires, No difference.. and all the while the CEL remained off.

Next I targeted the TPS as it sounded like it was either running lean or the timing was not advancing, in addition I disconnected the TPS and seemed to run fine other than an odd idle so I replaced it.... Now it does not pop but it idles rough and then slowly dies and bucks while driving during acceleration.

So...(sorry for the book) I am wondering if there could be another sensor that would cause this? like the Crank Sensor... I did eliminate the VSS, I unplugged it with no change.

I have a buddy bringing home a better reader to see what it spits out. Any suggestions would be helpful.

Thanks S

 

Check the Crank Position Sensor, make sure it hasn't crashed. Take it out of it's bore, look at end. If end touched triggers they're probably bent. Missing tabs also wig out the ECU. The wiring to the sensor also has a tendency to get heated by the exhaust and loose it's insulation and either ground or touch other bare wire. Connector is another item to check. Look for overheating lugs.

 

sounds like a timing issue. There's a bunch of things that affect timing, which on your truck I believe is electronically controlled by the ECU ?? Rave goes through a pretty explanation of what sensors affect ignition timing, and how. Do you have something like an Ultragauge that will give you real time sensor readings ?

 

Thanks for the info..

I am going to pick up a crank sensor and see where that takes me. I am just wondering if the ECU needs to be reset after installing the new suspect defective parts. I did disconnect the negative terminal and figured that should suffice.

As far as timing, yeah the crank, cam TPS and ECU control those, I was worried that my new cam skipped a gear but ruled that out early as it runs smooth on occasion and is backfiring through the Intake and not the exhaust.

97 SD 160K

 

Get yourself one of these

UltraGauge OBDII Scan tool & Information Center

Best sixty bucks you will ever spend. You will be able to get real time readings off of all the sensors that affect timing, including timing advance setting, while the issue is occurring and hopefully see which one is out of whack.

 

The timing is controlled by the ECU, but based on trigger from the crank position sensor. Even metal fuzz on the nose of the sensor can make it act bonkers.

With a scanner that shows live data you can look at TPS%, it will start at about 9% and climb higher as you rest your foot on the go pedal. Unless you are a major league pitcher, stop throwing parts at it. Eats up the bankroll quickly.

 

Got a real scanner and took a look... I cleared the original codes which indicated the cam position sensor end Evap codes. Put in a new TPS with a new pigtail and this is where it gets odd. Before I replaced the TPS, I unplugged the battery, disconnected the TPS, reconnected the battery and started it with the TPS disconnected. It ran MUCH better without the TPS connected either before or after I replaced it. You plug in the TPS and it almost acts like it completes a circuit with a short in it.

I checked the function of the TPS using a Scan Gauge, it is .8 at Idle and climbs when the accelerator is depressed. Then I tore of the engine wiring harness coating and looked for visible shorts or bare wires and discovered nothing wrong.

I am at a complete loss at this point...

 

Have you checked the MAF? CTS? You'll find the TPS and MAF are linked by a common circuit, how does it run with the MAF unplugged?

I assume you checked all the stupid stuff, like the intake boot for leaks(torn boot or loose clamp), connected the new pigtail to the correct wires, etc?