Sierra Issues - Now Fixed

[Dee 4x4]

Hi guys.

Just for reference purposes, here's what's happened with my Sierra over the last 5 weeks.

In an effort to annihilate my overheating issues, I did a full coolant flush with some damn expensive coolant and an additive to kill a minor leak in the radiator. I also upgreaded the 8" thermo fan to a 13" thermo. First run out, the thing would not overheat one bit. I was very happy.

Then I notice my power is dropping right out. I managed to keep the car going for a while longer but it felt like it was running at 50% power. There were no misfires and no smoke. Just utter lack of power and a silent (rather than loud) exhaust note from the 4AGE 20v. I limped back home, not being able to top 70km/h.

Diagnosis by the mechanics found a faulty AFM so I managed to track down a replacement 20v AFM in Sydney which I had sent up. However, upon attaching this, the car was now having electrical issues. The workshop spent a while diagnosing the problem but couldn't hit it so they had to send it to an autoelectrician. He proceded to find no less than 10 faults in the wiring of the car. As quoted by the mechanic in regards to the conversion, "It looks like he had all the right gear, but he really stuffed up on the electrics".

The 02 sensor was hanging 2" off the front pipe, relays and other wires were not soldered but just twisted together and in some cases not even shielded. Many other things. The root cause of all problems ended up being a stuffed 02 sensor as it has been clogged with mud.

The stuffed 02 sensor had in turn burnt out the AFM and has also rooted the CAT.

This has all been fixed now and I'm glad to have had all the wiring looked at and addressed so I don't encounter these problems when I'm out bush.

Including a new windscreen, the bill came to $1200.

Also, going back 3 months, the day after I bought the car the alternator died. This, including a service cost me $700. This was due to faulty wiring with some battery light sensor or something which burnt out the alternator.

So hopefully, now over $2000 later, I have a reliable little Sierra. The moral of the story is...

Make sure you get a reliable autoelectrician to do the wiring on your engine conversions.

Either way, all problems are sorted so now I can be happy and enjoy my new car

[Gutless]

The stuffed 02 sensor had in turn burnt out the AFM and has also rooted the CAT.

How is this possible??

The O2 sensor is in the exhaust manifold, and the Air Flow Meter is in the inlet pipe before the throttle body? They are on completely different sides of the vehicle...

If the O2 sensor was faulty, this would have casued the motor to go into safety mode, where it over fuels the car to stop detonation. basically it floods the engine. This would explain the stuffed CAT, as they tend to fill up with unburnt fuel and catch fire internally. The inside of the CAT will actually melt causing a major blockage and reducing power dramatically.

Once the ECM detects a faulty O2 sensor and enters safety mode, it usually just ignores the AFM's signal. I can not see the correlation between a stuffed O2 sensor on the outlet side of the motor, and the AFM on the inlet side....


Pete

PS. Glad its all fixed now.

[lay80n]

I agree with you gutless. The only way i can see it happening is if the actualy physical layout of the wiring was causing the issue.

Layto....

[Dee 4x4]

Something worth enquiring about then. Either way, the new AFM only cost me $70 delivered so no huge loss.

Unless as mentioned, it could have been the wiring which stuffed the AFM and not the 02 sensor in anyway.

They also mentioned that the AFM could have been stuffed from silicon used to seal it up leaking onto the electrics under high heat as the AFM had been opened before and resealed with silicon which is according to the mechanic, a bad idea.

Either way, I'll ask about it when I pick up the car tomorrow afternoon. The AFM was stuffed regardless and the wiring problems being redone should help me avoid problems in the future. I'm just hoping that it runs better than when I bought it which would be a bonus considering I was already happy with the performance when I bought it 3 months ago.

[Gutless]

They also mentioned that the AFM could have been stuffed from silicon used to seal it up leaking onto the electrics under high heat as the AFM had been opened before and resealed with silicon which is according to the mechanic, a bad idea.

This is actually true....sort of. regular silicone actually does destroy some sensors over time. You can however buy sensor safe silicone for this application. Sounds like you did need an AFM, but it would hardly be related to the other issues.

Pete