When is a bad MAF not a bad MAF ?

[ninedee_golf_tdi]

A friend has an a4 alh, low specified/actual MAF readings, unplugged the MAF harness, default of 550 made the car run well. Replaced with a new Bosch MAF, same low readings. He says the egr looks to be opening/closing. So...... what else could over ride the MAF to cause the low readings. Yes, an air leak somewhere, anything else ? Thanks.

 

[Mozambiquer]

Boost leak, stuck EGR, failed camshaft, clogged intake.

 

[burpod]

i hate to state the obvious, but check all the wires. i just had my first maf problem in wife's golf BEW - which has a map-based tune so i didn't think a bad MAF wold affect it, but i just getting a low-signal code for the MAF and it was limiting fuel to 32mg, and rather slow (i believe because of the MAF code, not sure why else it would limit fuel, nothing else appears to be wrong). i fiddled around with the connector, nothing. the next day when it was light out i started tugging on some wires, and apparently a mouse had chewed threw a couple wires to the MAF... hopefully reconnecting those will fix it. painfully slow :/

 

[ninedee_golf_tdi]

I spent a few hours looking at this 02 5speed car yesterday. Car was recently purchased with it running with no power. Intake was recently cleaned, don't know about the head runners. EGR is working. Exhaust was replaced so no plugged up kitty kat. Didn't pull the valve cover but that doesn't seem to be the cause. Appropriate vacuum everywhere. Every accessible wire harness was inspected, no defects noticed. Ran the engine without the air filter to rule out snow screen restriction. Checked for shop rags plugging up the boost tubes. Classic symptoms of bad maf with readings (295/295) and performance, runs better with (new) maf unplugged and at default of 550, but falls on its face above 2400rpm. Maf won't go above 295/350-375 when stomping on it (harness connected). The IP was recently "resealed" but is leaking. IQ is 6.3 but I didn't want to chance making the leak worse by hammer mod. Timing belt was previously m&p, but crank and pump are in time and timing reset from above the graph to 65+/-. All basic ecu settings checked and were at default. Injectors appear to be original. No codes. Any ideas ?

 

[ghohouston]

Electrical problems can cause some weird issues and not exactly throw codes to point you in any direction. Can't say for certain on this m.a.f. issue on a Vw, but have dealt with it on an excavator. Another mechanic at my company diagnosed machine as having a "bad turbo". I get handed the job and told to replace the turbo. I do so, and find it's still very low on power. Connect the engine diag software, and find the boost reading never changes, but is reading somewhere around 5 p.s.i. spent all of a minute looking in the engine bay and found 1 of the wires going to the boost pressure sensor broken. Repaired that and the machine came back to life. It had no codes, not even boost pressure related.

 

[oilhammer]

Send the injectors out for a good (professional) inspection. I'd probably also send the pump out, since it is leaking and was clearly butchered by your description. While the fuel system components are being evaluated/rebuilt, you can get the timing belt stuff all ready.