Author Topic: Air flow meter 450  (Read 4528 times)

ulodzi

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  • Posts: 8
  • Location: Australia
Air flow meter 450
« on: 07 June 2004, 02:43 AM »
I have just had a pre ignition on gas and now cannot restart. I suppose I have damaged my airflow meter. I will read the manual tonight and check in the morning. Has anyone had this one before

Tremix

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  • Posts: 5
  • Location: Philadelphia, PA
Air flow meter 450
« Reply #1 on: 09 June 2004, 04:46 PM »
Almsot sounds like your fuel mixture is too rich. Disconnect the fuel pump relay and crank it with WOT (wide open throttle) to clear it out first. Check for leaking injectors, cold start valve. If the car hasn't run in a while - a year or so - be sure to check the fuel metering rod (that goes into air meter).

The air meter is a pretty sturdy piece, unlike the modern wire systems. Backfires aren't likely to damage it right away, although it isn't very healthy for it either of course.

ulodzi

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  • Posts: 8
  • Location: Australia
Air flow meter 450
« Reply #2 on: 17 June 2004, 04:41 AM »
I should have been more precise. Gas to us is liquid petroleum gas. I have subsequently found that I can get the car to run on petrol by depressing the airflow meter. Unless I depress the plate the injectors are not functioning even during cranking. I am about to try an exchange of flow meters from a known runner. I am starting to ask myself why I couldn't start on LPG. The airflow meter would be irelevant. I suppose I will be searching for a loss of vacuum or a damaged diaphram on the gas system.
More later

gordonperry2003

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  • Posts: 5
  • Location: Scotland, UK
Air flow meter 450
« Reply #3 on: 25 October 2004, 02:47 PM »
I think I can shed light on your problem.  Sorry it's so late since your question, I just found this site today.  

If there is no fuel pressure (petrol) when cranking, then suspect the control for the fuel pump relay.  This can be checked by feeling the relay for a "click" as it operates - it is located in the fusebox.  By depressing the plate in the intake, this activates the relay and is how the pump remains activated when the engine is running after cranking has stopped.  It also acts as a safety feature by cutting the fuel pump when the engine, and the airflow, stops.  

I hope this makes sense.

GP

ulodzi

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  • Posts: 8
  • Location: Australia
Air flow meter 450
« Reply #4 on: 25 October 2004, 07:35 PM »
Unfortunately your response is timely. I have just done it again - backfire on changing to LPG.
You were correct. The relay was not working. I changed the whole assembly ,refitted the LPG and had the petrol side set on the osciliscope at the dealer.About 6000 k of happy motoring
I am discovering that many people here are running their 450's on LPG and the airflow sensors are becoming harder to find 2nd hand. My US service manual says there is a kit to replace the deflector plate. I have pulled down one of my collection of damaged units and if damage is limited to the plate this might be a solution. More later on availability.
I have been watching top fuel dragsters. They have a blow out plate in the manifold to protect the supercharger from backfire.The airflow sensor body is certainly large enough to accomodate.
The premium option would be to stop the backfire???

gordonperry2003

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  • Posts: 5
  • Location: Scotland, UK
Air flow meter 450
« Reply #5 on: 26 October 2004, 06:12 AM »
Hi again

Glad to have been of help.  LPG is black magic to me, so no ideas on the backfire!  

GP

ulodzi

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  • Posts: 8
  • Location: Australia
Air flow meter 450
« Reply #6 on: 07 March 2005, 01:36 PM »
The steel disc attached to the arm of the airflow sensor on the M117 is sacrificial in the event of back fire. The kit is about $30 at the dealership and easy to fit with the airflow sensor unit out of the car. If I have the problem again I will have a go at doing it in car. Adjustment for height and centre is critical and is covered well in the Workshop Manual on this site.I have learned two things about LPG. Keep the ignition system in good condition and don't touch the throttle when starting or changing fuel