MAF Problems after big tuneup

**Mattskii** · 14th March 2011, 01:41 PM

Well, I still have not taken her to the experts. Work is looking hazy again and I don't want to spend too much untill I have some certainty in what work I will have over the next few months.

History: 96 D1 V8i not starting properly. Checked overr all the usuals, with much help from this board.

I was reading this :Fuel injection

So I went to make some changes to the setup.

Set the CO trim back to an output of 1.8volts as per factory settings - we changed it to 1.3 as had read online somehwere it was a good option. Will see if having it at 1.8 is any different. It did seem to make a change to to the idle engine speed.

Then I decided to set this too. Blocked up the pipe from the throttle assembly to the plenum as per instructions and connected the multimeter to the coil to get an accurate measure of the RPM (Apparently the tacho is showing about 500RPM under what the engine is actually doing, according to the multimeter) With pipes blocked and engine running set the RPM to 620 steady turnover. Then reassembled and restarted, the engine idles at about 760 to 830, but is hunting quite badly.

Checked the MAF next. According to the page above page:

Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts after the initial "warm up" spike. Most defective airflow meters will overshoot to 0.8 Volts or higher, and take at least 2 seconds to come down to the correct voltage.

Mine does exactly that - jumps to about .88 V then drops to .34 over 6 to 8 secconds.

At normal tick over it should be 1.7 and that is about what I am getting. Odd. I can see the figure increasing as I rev, so output is varying with airflow as it should.

So my new starting proceedure will be to wait 6 or 7 secconds for this reading to get back down to normal before I try to start - I won;t know if this works untill tomorrow morning when I start it from cold again.

Still wondering if I should replace the MAF though? Thoughts? And what about it hunting a lot at tickover? Do yo uthink it set idle too low? It suggests 600 with pipes blocked, but I only went down to 620 as I was worried about this. Now it idles (hunts) at between 760 and 830 rpm.....

Well, we will see if this helps it start at all..... it has been really bad this last week, not wanting to start without much help from the throttle.

Any other ideas still very much welcome!!

**Mattskii** · 14th March 2011, 02:18 PM

Quick update - still not starting well from hot. Pah!!!!

**PhilipA** · 14th March 2011, 02:32 PM

1.8 volts is for the US/UK market with O2 sensors. I cannot see any compelling reason for this although it may be easier for the ECU to take fuel out rather than add in when the o2 sensors are controlling idle mixture.
In australia it should be about 1.2volts depending on HC reading from tailpipe sniffer. At 1.8 volts it will be very rich on idle and subsequently across the board.
Fluctuating revs is most probably the IAC.
Regard sPhilip A

**Mattskii** · 14th March 2011, 04:28 PM

Originally Posted by PhilipA

1.8 volts is for the US/UK market with O2 sensors. I cannot see any compelling reason for this although it may be easier for the ECU to take fuel out rather than add in when the o2 sensors are controlling idle mixture.
In australia it should be about 1.2volts depending on HC reading from tailpipe sniffer. At 1.8 volts it will be very rich on idle and subsequently across the board.
Fluctuating revs is most probably the IAC.
Regard sPhilip A

Oohh, thanks for that! It is running too rich already, I guess I just made it worse? LOL - OK - going to pop out and drop that down again now.

Cheers

**justinc** · 14th March 2011, 05:29 PM

Fuel rail temp sensor aids in hot start, ALSO, Dirty and dribbling injectors can cause all of the above. Have you had a fuel pressure gauge on at the rail?? What does it do before start, during idle, with the vac hose to the pressure reg crimped, after engine switched off?

JC

**Mattskii** · 14th March 2011, 06:22 PM

Originally Posted by justinc

Fuel rail temp sensor aids in hot start, ALSO, Dirty and dribbling injectors can cause all of the above. Have you had a fuel pressure gauge on at the rail?? What does it do before start, during idle, with the vac hose to the pressure reg crimped, after engine switched off?

JC

Yeah - I checked the fuel temp sender - seems to be working OK.

I don't have a fuel pressure guage, but if anyone in Melbourne would be willing to lend be one I think it would help me out big time. I have a strong susspicion that the injectors are a problem because A) The plugs are blackened, and B ) 2 of the plugs are damp.

**justinc** · 14th March 2011, 06:28 PM

Originally Posted by Mattskii

Yeah - I checked the fuel temp sender - seems to be working OK.

I don't have a fuel pressure guage, but if anyone in Melbourne would be willing to lend be one I think it would help me out big time. I have a strong susspicion that the injectors are a problem because A) The plugs are blackened, and B ) 2 of the plugs are damp.

When looking for overfuelling or poor starting faults with an old 14CUX system, a pressure gauge should one of the most important diagnostic tools.

JC

**Mattskii** · 14th March 2011, 06:54 PM

Originally Posted by justinc

When looking for overfuelling or poor starting faults with an old 14CUX system, a pressure gauge should one of the most important diagnostic tools.

JC

That may well be, but I don't have one.

**shaunp** · 19th March 2011, 07:00 PM

I've the water temp sensors go open cct when hot which richens the mixture, causing them to flood and not restart, hard to find as it only happened when the engine was really hot.

Thread: MAF Problems after big tuneup

Thread Tools

MAF Problems after big tuneup

Bookmarks

Bookmarks

Posting Permissions