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Discussion Starter #1
Hi all

I have a bit of a dilemma at the moment. I've just replaced a radiator, hoses, and heater pipes (with hoses).

Prior to hooking up the final radiator pipes to the radiator at the front, I connected the two front to back pipes to recirculate and bypass the new radiator. I filled and flushed to remove anything unwanted prior to hooking up the radiator. Started and warmed up, also kept topping up fill cap with water to flush. It never moved passed operating temperature, and once thermostat opened I stopped the engine. Job done, so I thought.

Drained the fluid, connected in the radiator, and re-filled. Car wouldn't start. It turned over ok, but wouldnt start. A quick pop on the ignition and it would sound like it might fire up, but a prolonged try and it would just crank and crank.

I started with fuel. Replaced the fuel filter, removed inlet on rail and plenty of fuel came pouring out when cranking.

Next I looked at spark. Each plug and lead is producing spark..

Removed the plug from the AFM, and it started. I does not idol correctly, and is super rich, but it would run. Interestingly, plug the AFM back in and rev's pick up for a little, then it dies. Even after this, the car wont start with AFM plugged in.

Anyone had this issue, or have any ideas on what might be causing this?

I've been chasing my tail all day, testing sensors, resistance on AFM etc etc. Could be completely missing something easy here (I hope!).
 

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Discussion Starter #2
Further to the above, worth noting that was receiving 14+ volts on the multimeter the first time in ran and was flushing the system. More recently, it seems to be running of battery voltage only.
 

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Everything I provided was irrelevent.

See if opening the AFM manually makes a difference, or check the resistance values on each pin.
 

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Discussion Starter #4
Was trying to give full background in case something was missed, so your saying none of it should make any difference?

I'll try opening AFM manually. It has been opening though, cause when you switch off, or engine dies I can hear it snap shut.
 

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Those AFM’s are finicky... did you pull off the connector (clip) or remove the two AFM screws? It’s been done!! The two screw are the circuit board and you will ruin it if removed... I hate AFM’s
 

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Discussion Starter #6
Yeah it sounds like they are a pain. What I cant understand is that it was running the same day, then not at all. No major change, except more water and a radiator in the system lol.

No, the screws are in tact and its only been removed via the clip on the plug.
 

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Discussion Starter #8
Update, tried the above suggestions.

Opening the AFM manually had a worse effect.

Tested the AFM with Ohmmeter. The initial resistance readings are good, including the temp sensor. I also put a hair drier in there and the temp sensor responded by dropping resistance, so thats good.

When I measured resistance of the meter at full shut (approx 590 ohm), then full open (approx 70ohm), I noticed that I got an infinity resistance reading for a short time before a resistance reading. I also noticed that there was infinity resistance reading at some points through the movement, with it not giving me a reading at all (say just barely open, 3/4 open etc).

I also tested voltage from the wiring harness to the AFM, and I'm getting the 5v.

Also measured voltage between the VS wire and E1(from back of harness) with the plug in the AFM and the ign on. I was getting 3.85v with no throttle, and no change up to full throttle (3.85 constant).

Check the message here about testing AFM which relates to the above testing.

You gotta test for 3 things.

1) you need to make sure your AFM is getting a good signal and has a path to give a good signal back to the ECU. So you test your AFM harness for that. So, VC on the wiring harness end grounded to E2 should net 5 volts.

2) you need to ohm out the potentiometer inside the AFM to see if its actually working. Thats the OHM reading the BGB lists.

3) Plug the plug in and use the lead on the tester to penetrate the rubber sheath so you can get a reading on the VS wire with the AFM working. With the ignition set to ON, the VS wire should read close to 5V with NO throttle, and it should taper down toward 0v as you approach full throttle.

If your AFM passes all these tests, its likely "functional"

Any thoughts out there??

Thanks all
 

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The AFM needs to have good contact on the pot and the resistance on the strip has to be uniformly increasing/decreasing, any etched spots where the coating has worn away will cause weirdness like this.
 

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Discussion Starter #10
The AFM needs to have good contact on the pot and the resistance on the strip has to be uniformly increasing/decreasing, any etched spots where the coating has worn away will cause weirdness like this.
Ok thanks, and has that caused the same issue I seem to be having? I just want to try to make sure I have narrowed down the problem before I get another AFM to try.
 

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Ok thanks, and has that caused the same issue I seem to be having? I just want to try to make sure I have narrowed down the problem before I get another AFM to try.
If the AFM is dead at the low load point then yes you will have a lot of trouble with starting the car. The ECU has to have accurate airflow data to start the car, otherwise fueling will be completely off.

Once you diagnose most issues I would just bin the AFM and run a Link with a MAP sensor instead.
 

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Discussion Starter #12
Ok so tested the AFM again, and its definitely sending voltage with the vane fully closed (3.86v), and also fully open (0.46v). This to me says its working, so back to square one.

Link? I don't really want to go down the road of new ECU, tuning, and all the potential issues that come with.

Any other ideas as to why when I unplug the AFM it starts (although not very well and very rich), plug it in and it idols well for about ten seconds then dies?
 

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It may be the wrong path, but you're positive you don't have any vacuum leaks? My car refused to run with the AFM plugged in because of a decent sized vacuum leak. it would do exactly the same thing you described.
 

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Discussion Starter #14
I've had a look for vacuum leaks, and run a smoke test but couldn't see anything. Where were you getting your leak from? I have a JDM model, does anyone have a diagram of the vacuum system, and what should be connected to where? I may be missing something...
 

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Check the piping from the AFM to the turbo inlet and from the outlet to the intercooler and from the intercooler to the TB.
 

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I've had a look for vacuum leaks, and run a smoke test but couldn't see anything. Where were you getting your leak from? I have a JDM model, does anyone have a diagram of the vacuum system, and what should be connected to where? I may be missing something...
mine was from an improperly installed intake manifold gasket.
 

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Discussion Starter #18
Fuel pressure problem! Fixed! I was getting flow, but barely any pressure. Turns out the Wahlbro fuel pump had come loose and broken the rubber hose it was connected to inside the tank. Out and in went the pipes and tank again! Glad to have found the problem, and thanks to everyone on here for their input.
 

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Great discussion here. I don’t want to throw anyone off track. It’s been a few years since I’ve dug into my ’91 Turbo MR2.

I dont recall whether MR2s have this feature, but I had a ‘70 something Chevy Monza with an engine cutoff switch if there was no oil pressure. Just a thought.
 

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Great discussion here. I don’t want to throw anyone off track. It’s been a few years since I’ve dug into my ’91 Turbo MR2.

I dont recall whether MR2s have this feature, but I had a ‘70 something Chevy Monza with an engine cutoff switch if there was no oil pressure. Just a thought.
It's not a feature on these cars. (y)
 
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