Volvo 940 Engine speed signal

I think you are looking in the wrong directly currently. The engine speed circuit obviously is working because the car is running.

The manuals were written for these cars before modern test equipment was widely available. The test procedures may be outdated.

ZVOLV said:

I think you are looking in the wrong directly currently. The engine speed circuit obviously is working because the car is running.

The manuals were written for these cars before modern test equipment was widely available. The test procedures may be outdated.

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I?m not following any manual, I was just looking at the documentation made by ipdown about the ecu and saw that the volt was lower than he specified, however now I?m not sure about it since my multimeter is a cheap one.
Ofcourse the car runs, however if the voltage really is lower then maybe the fuel ecu is seeing it as a lower rpm than it is? The ezk is still getting the corect signal, so ignition timing will be right, just that the amount of fuel calculated by fuel ecu is MAF table x rpm table, not exactly simple math like this, but you get what I mean and below 3000 rpm it uses the lambda control, so it caps at around 14.7 AFR, but after around 3200 rpm AFR goes up above 15 and then above 4000 it gows down to 11.

Basically my thought process is that since fuelpressure and injectors are good it can only be maf or engine speed signal and since the maf seemed to have corect value and the engine speed has too low votage, if my mutimeter is corect. Then I assumed engine speed signal is wrong. But I have ordered a maf now anyway so we will see next week if that solves the problem.

MAF's are one of the sensors that you can't really test without just trying another one. They can read "in spec" but still be skewed enough that the mixture will be off. Especially on these old EFI systems.

Today when I was driving my sister she asked me what’s making all that noise and I said it’s just my fuelpump and then it occured to me it is pretty loud. Maybe a little too loud and maybe it means I have an air leak in the fuel system. However this is a heavy duty fuelpump after all and it sits directly under the pedals, so it’s quite noisy.

Here is a video of the sound, what do you guys think?
https://streamable.com/qi2av4

Another thing that happened today was that the car didn’t want to start and I had to give it a little gas for it to start, like it didn’t wanna rev up. But then it ran normally.

Now I got the new MAF and for sure the old one was broken. The old one would increase alot slower on lower rpm. But now I’m running too rich instead... on 5th gear I get 10 AFR already at 2500 rpm and the gauge I’m using only show as low as 10, so god knows how rich I’m running. Faulty MAF again or any other ideas?

Noone got any ideas?
I really need my car to work because this is my only car running atm.
And with the old maf it get too little fuel and new one too much, could it really be the maf again or do I have some air leak that I can’t find or some other issue?
As of now I really don’t like to drive the car because I’m scared I will break something when it gets so much fuel.

Are you running standard fuel pressure again? Have you checked that the fuel pressure regulator is working correctly and that the vacuum line is dry (what's the pressure at the rail at idle and at 2500rpm)? I'd also check carefully for air leaks all the way from the MAF to the head.

bobxyz said:

Are you running standard fuel pressure again? Have you checked that the fuel pressure regulator is working correctly and that the vacuum line is dry (what's the pressure at the rail at idle and at 2500rpm)? I'd also check carefully for air leaks all the way from the MAF to the head.

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Yes the pressure is set to standard; and I have checked for air leaks. I also find it unlikly if it is air leak since on max boost I have good afr, it’s only when boost start to come it gets too much.. if I had air leak it should run even richer on max boost right?

The vacuum hose is dry and if I rev the engine it increase the fuelpressure for a little bit and then go back to normal, like it should.

The car went from using 9 liter per 100 km to 13 l. So right now I’m driving with lower fuel pressure, but even now it show 10 afr sometimes. It’s so weird.

I made a video showing the AFR.
The 11.02 mark was hit aroune 2500 rpm and then it started to run leaner, even thought I did not stop to accelerate and then @ around 4-5000 it start to run too lean because right now I have too low fuel pressure, but how come the car get this much fuel around 2500 rpm even with lower fuel pressure??

Also when I start the car it has 10 afr until car is warm, with old maf I had 12-13, which I think is more normal. I’m thinking if I have an air leak it should run too lean @ idle because of vacuum, or am I thinking wrong?

https://streamable.com/jpdkfx

I did some readings today. At idle it’s pending between 2 and 2.1 bar, when I rev the engine it increase to 2.5 and according to my boost gauge I have 0.5 vacuum, so it seems ok.
If I hold the rev up it goes down to 1.9 due to increased vacuum, so seems to follow vacuum/boost pretty good.

However this means I’m now running with 2.5 fuelpressure instead of the standard 3 and it’s still running rich when boost comes and ofcourse running lean at max boost. Can this really be an air leak?

Anyone got any more ideas?

Today I messured the maf voltage and it was only 4.7 @ 6000 rpm, so no wonder I’m running rich. So I installed the old maf and it also only show 4.7, I remember last time I checker it read 5. What could have happened?

Also I noticed at idle the new one show 2.5 and old 2.3, so that’s why I’m running super rich cold start with new maf.
Could this be wiring issue, even thought I get the 1.4 volt like I should when I turn the key?
Or is both my mafs faulty?
Or am I just really bad at finding air leaks, got any good tips how to check?