Thread: AAARRGGHHH!!! td5 disco

with the overboosting issue in general, when the td5 is chipped/flashed, does this do something to raise the ecu's threshold of what constitutes overboost? i assume the power upgrade comes from injector timing and duration as well as increased turbo boost. am i somewhat right?

It's hard to tell when you are not there to drive the Disco but,..

Does pretty much sound like the MAF in early failure mode, or plug that connects the MAF to the loom. Also check the 2 cent plastic loomtube has not crumbled away where it runs over the air cond compressor, the wires may be sitting without shielding on top of the compressor slowly melting onto it.

Disconnecting the plug to the MAF will force the ECU to run a factory preprogrammed fuel setting. The engine will not surge with this, if everything else is OK. The TD5 ECU is designed like all other computer controlled engines to run with a MAF.

Without the MAF connected the TD5 will seem docile until you floor the pedal and turbo boost pressure builds a bit. Also keep an eye on the tacho when the pedal goes down and hang on. Don't rev the guts out of it, back off when you think all is good and you have passed the point where it normally surges. Try it twice to convince yourself you are in the same Disco II TD5.

Also a good test with MAF disconnected and on straight stretch. From D put it into 3 and then floor it. Quite exciting experience as boost is already up and you accelerate in the lower gear. Absolutely great fun if are a Rev Head (like me).

As for boost, my waste gate is adjusted fully closed with the engine off and has been that way since a new MAF was fitted to my TD5 over a year ago.

I read that the ECU will not go into overboost (shutdown) protection until 32 psi on the inlet side is reached. All functioning normally the watsegate modulator will keep it well down from there and I seriously doubt in normal circumstances it would ever get to 32psi. (Runaway, yes)

The best I could get out of the TD5 revving the c..p out of it in Park with no load was 26 psi. My gauges are old and probably reading about 1-2 psi lower than accurate.

The wastegate actuator via the wastegate modulator and ECU is going to regulate the turbo and hence input boost for you if all is functional. Screwing the wastegate up will just get the same boost psi on quicker. The controls will still open and close the wategate at the same pressure points.

Warm the engine up, turn off and disconnet the MAF. Take it for a drive flooring it down the road and see if it still surges. If not you have either a bad MAF, plug or wiring. Borrow a MAF from someone if you can and swap it to see. 10 minute job.

Still surges you have something wrong in the air pressure line after the turbo losing pressure or turbo modulator sensor, hoses to sensor or wategate actuator or wastegate. Check the inside of air pressure hoses are not coming apart or no holes. Your fuel pressure block could also be a bit tired compounding the problem but not actually causing it.

EGR could be stuck open diluting the oxygen level, but this usually results in loss of power and very poor fuel economy, more so than surging.

Sorry to woffle on so long.

BradM