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Why does my cars' speed drop suddenly when driving fast ?

My friend cut the mass air flow wiring on my 2006 mk2 focus 1.8 TDCI because we discovered the ends of the wires were torn after the diagnostics test revealed maf sensor circuit a open.
He ran out of wire and botched up the job and said he'll finish the job when he get's more wires, says he'll just fuse them on. that was several weeks ago and I am still waiting for him to do it.

Anyway , next day after he cut the wires, I was driving on the motorway and about to do a overtake, once I got to 70 mph I feel a tiny little thud, ( almost unnoticeable) and then my car refuses to accelerate and very slowly my speed began to fall and whenever I tried to accelerate again it would accelerate very slow.
It's happened a few times since, usually once I get to 70 mph it happens, though very rarely I can accelerate past 70 mph + with no speed fall .
Glow plugs have been out and tested and all seem fine, all glowing when tested.

Am I right to think it's because of the situation with the maf sensor wiring ?

as problem only began after cutting wires.


thanks
Reply 1
Avatar for JC.
JC.
19
ECU doesn't know what to do as no signal coming to it.
Glowplugs are only used to start the engine. After that happens they do nothing. You don't even need them on a lot of diesels if its warm enough outside. I certainly don't bother using mine in the summer.
Reply 2
Avatar for Nuffles
Nuffles
19
Sounds like an intermittent short or fault. When the ECU can't see the MAF reading it defaults to a 'safe' MAF map so the engine will run, but badly. Is this the same idiot that did your EGR valve and thought it was a 'big job'? You need a new friend! Why did you let him start a job he couldn't finish?
Which side of the connector is the wiring damaged? If it's on the sensor side I'd just get a new one or pull one from a scrappy. If it's on the loom side your options are a bit more limited...
Reply 4
Avatar for Nuffles
Nuffles
19
Original post by CurlyBen
Which side of the connector is the wiring damaged? If it's on the sensor side I'd just get a new one or pull one from a scrappy. If it's on the loom side your options are a bit more limited...


Most I've seen have the socket directly as a part of the MAF, so it's most likely loom side. His best bet, if he doesn't want to spend even more money, is find a friend who can actually solder and then pull the loom out of the same car at a scrappy and graft it in. I've done this on one of my cars and it worked fine! I'll probably have to do it again on this car, some muppet routed one of the looms wrongly and it's been rubbing on the filter box for who knows how long *sigh*.
Original post by Nuffles
Most I've seen have the socket directly as a part of the MAF, so it's most likely loom side. His best bet, if he doesn't want to spend even more money, is find a friend who can actually solder and then pull the loom out of the same car at a scrappy and graft it in. I've done this on one of my cars and it worked fine! I'll probably have to do it again on this car, some muppet routed one of the looms wrongly and it's been rubbing on the filter box for who knows how long *sigh*.


I'd suggest crimping rather than soldering if possible, crimped connections are more tolerant of vibration. To be fair a soldered joint will probably last a few years which may well be the remaining life of the car, but intermittent wiring faults are an absolute nightmare...

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