[K11] Stalls when warm...

Lex_Michdemicra

Lex_Michdemicra

It's been quite a while that I connected my laptop to the K11 and I think I forgot about 90% of my knowledge of Datascan somewhere between my ears. For the record: I made this video



So in 2015 I have re-flowed the MAF. That doesn't mean it can't be bamboozled again, but the video above shows how I re-flowed it. I was cautious not to leave flux behind as you can see, so corrosion is unlikely...

When the car is warm it wants to stall (and does so) when idle. The first thing I thought about was the MAF and so I grabbed my laptop with Datascan and my Consult cable to see if my gut feeling was correct. "Unfortunately" the 'air flow sensor' stayed clean (no DTC's and no erratic behavior). But it came to my attention the O2 sensor was all over the place. To me it is a bit of a 'chicken or the egg' story (is something wrong in the engine and then the O2 sensor goes haywire or is the O2 sensor going crazy which makes the engine run bad...). Maybe one of you guys can help me out.

When driving I remember that during engine braking it showed me it was giving a RICH mix to the engine. If I recall correctly it should show LEAN mix. All the time the O2 sensor acted very nervous.

In the Datascan software you can select 'Base idle adjustment'. When I click this the engine drops drastically in revs (below 350) and eventually (after a few seconds) stops running. Should I tamper with the set screw to get the revs right now or should I try to fix my erratic O2 sensor first? I don't know what to do. What is the correct behavior of my O2 sensor? Could this cause my revs to drop when I select 'Base idle adjustment'?

Shoot!
 
If you select base idle adjustment with a warmed engine (fan came on and off) you need to adjust to 850 rpm. That is your starting point. For the rest, let me think if I can write something helpful.
 
I've found something. My car had an air filter being replace for a more strict one. By setting base idle adjustment to on, engine died. This was with warmed engine. I've noted that with no warmed engine, putting base idle adjustment to on made the engine running but a hundred rpm below 850. I've just adjusted that roughly and now I can use base idle adjustment with warmed engine. Some drivabillity issues of many I have, has dissapeared.
 
I am late with my reply, sorry for that. I just wanted to find out what was wrong with it before responding here. After my first symptoms I decided to turn the idle adjustment knob in the base idle adjustment setting really quick and set the RPM to 700-750 (can't remember exactly). The problems were less frequent and it ran acceptable. I changed the lambda, because I didn't trust him, but it didn't change the behaviour. Bosch says you should replace it every 100-150k KM (car has done 220k now), so I thought it would be a good thing to try. If it didn't help, I had at least performed proper maintenance.

This week the car really started to give up. I even lost a cylinder! That gave me a helpful clue though; ignition? Injection? Throttle body? I got a replacement throttle body just to see if the problem would be in there. Taking the intake filter box off, I decided to test the injectors (measure the resistance of all injectors, should be 11,5 ohms) and number 4 proved broken (resistance was infinite). So I guess the problem (could be) solved. In the coming week the new (used) injector rails will come in (they only sold a full rail, paid 35 euros so no problem) and I will replace it. I think the injector was giving up intermittently (those problems are the most difficult to solve), glad it gave up completely so I can finally fix it.

I'll follow this up when It has been replaced, thank you for playing.
 
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I see. So this throttle body came equiped with TPS, AAC and MAF?

I just replaced injectors and I replaced all four of them because that is better then replacing one for obvious reasons but of course all four need to be proper then.

For the fuel rail, if there is a FPR on it, you might want to test which one is best. When I put the other four injectors in my engine with a unknown status fpr, car took the injectors and run instantly quite rich. I heard ecu guessing, ecu's saw that instant. Then after driving (less then 5 miles is has been learned) I put back my original FPR, ecu saw it instant ran lean (but this you won't notice that easy) and still like car was hitting gas pedal several times. I decided to stick with the original but this doesn't mean I am correct about this. But it makes a difference, how ecu saw this I can only guess, maybe it noticed the air fuel ratio changed quite a lot instantly based on it's learned values and/ or base mapping.

Of course it is easier to test the FPR's with a fuel pressure meter but people usually don't have access to one. And the best way to get one is to find a competitive priced adjustable FPR with pressure gauge, I have one but I decided to not install it because of my clean engine bay and this big ugly meter that also turned out to be a Nismo replica. But that is another story, it might give you some good ideas.
 
I didn't replace the throttle body yet, I stumbled upon the broken injector first. So I will be replacing the injector later this week and if it runs like it should, then I am not touching the original throttle body.

I am getting a used rail in the mail, so I will first inspect how they look. If they're looking good I'll clean up the rail and replace the whole thing (do I need a kit with new O-rings or gaskets?). Is the FPR the vacuum thingie? I can reset the computer in my Datascan software, but it's good to know that the original rail is preferred. I guess the ECU has gotten pretty crazy info when the injector failed (my gf drove it for quite a while after it failed, she had to get home of course), so a reset will be a very good idea.

I don't plan on modifying it to do track days (it's my gf's car), so I don't think it needs anything adjustable. OR if it makes it use less fuel, then it might be something worth looking into, but not in the coming weeks.
 
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Original rail doesn’t matter they’re all the same. Fpr specs are all the same unless you have a broken one ofcourse. Or forget to connect the vacuumhose.

You don’t need new o rings but when the old ones are hard and old it might be handy to give them a bit of lube or oil.

I’d also replace the fuel filter while your swapping the rail. Easy to do and dont forget to pull the fuel pump fuse and try to start it to empty the rail.

And disconnect the battery before you start working on it. This will also clear the self learn.
 
For the o-rings, I did replace them once because it where cheap parts but after replacing another fuel rail I decided that some polishing on the rubber and maybe on the aluminium where the o-ring is seated to remove corrosion, put some wheel bearing grease on it and trust to this after this little inspection and reworking to just leave them there. My air leak is really somewhere else. And the fpr is that vacuuum thingie indeed. More vacuum means more pressure but how the ecu can control this is what I would like to learn.
 
ECU doesnt control fuel pressure. The FPR is in place to give it the right fuel pressure .The one the ecu is programmed for, 3bar without vacuum, somewhere around 2.3-2.5 with vacuum as the vacuum lowers it and not raised it as you said. The ecu controls the duty cycle of the injectors.
 
.Maarten said:
ECU doesnt control fuel pressure. The FPR is in place to give it the right fuel pressure .The one the ecu is programmed for, 3bar without vacuum, somewhere around 2.3-2.5 with vacuum as the vacuum lowers it and not raised it as you said. The ecu controls the duty cycle of the injectors.
Click to expand...

I see. Then I am mistaken. So an adjustable fuel pressure regulator will have a sweet spot somewhere and 150 k miles old original fpr's can go old and give unexpected pressure and the ecu guestimates this with it's lambda in the first place?
 
It has to be within specs. Old or new. Its not really a service part but like everything it can break. They can be tested by connecting a gauge between the injector rail and the fpr. No the ecu will not guess what the fuel pressure is. It will just think it is whatever is programmed. The ecu controls the duty cycle by calculating it with the values it gets from all the sensors like lambda and maf.
 
Okay. Is there really magic involved with the injector times and duty cycle length? Or is it just me? I tried to look this up on the internet but it seems generic knowledge I don't have about it? I always wondered where the duty cycle length comes from. I am aiming for best mileage, best mileage works as long you drive nicely. I ask this because I have no comparison material about a runs like new stock Nissan engine from the old days (1993).
 
Theoretically yes. Most likely no. Tuning an engine isnt as simple as just changing some numbers and youre done. You need to know what youre doing and how everything works together and what happens when you change something. A good tune will not make much difference in power. It will make the difference in lasting 500 miles or 500000 miles.
 
.Maarten said:
Theoretically yes. Most likely no. Tuning an engine isnt as simple as just changing some numbers and youre done. You need to know what youre doing and how everything works together and what happens when you change something. A good tune will not make much difference in power. It will make the difference in lasting 500 miles or 500000 miles.
Click to expand...

Thank you. I can't help myself, when I conquer my daily driving issues like mild throttle bucking because WOT feels good already (which tells me nothing though), I want an ecu that I can set (with the homework for understanding), find out my ideal 'I advanced my timing quite a lot but avoid engine damage spot' and then learn where my engine starts lacking breathing, fix that, then decide if I want wilder cams and somewhere in between a fiddle around ecu. Thank you for letting me hijack your topic Lex_Michdemicra ;)
 
I'm not sure where I left off from this project, but I finally got a chance to get back to fixing this. After replacing the injector the problems were gone, but not completely... I have no idea why, but the last month it got really annoying again (stallin when idle and even killing the engine, the typical solder problem) and I decided this afternoon I was going to take off the throttle body and take a look at the soldering...

Of course I forgot to take high resolution photos, but I think I saw cracks in those three prominent solder points outside of the pcb (you know the ones I mean). I have a desoldering gun, so I took off all the solder on the 6 points (one on each side) and used new solder on all of them.

I hope this will fix it finally... At 230000 kms it starts to get harder and harder to want to fix it. I don't have a proper workshop anymore and the rust is catching up on me. Even the strengthening structure on the bottom of the bonnet is rusting off! And the sunroof starts to grow without our permission...

-edit- Had a good test run today, problem solved. Let's see what will happen before we touch the 300000kms... Thanks for playing.
 
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