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D40/YD25 issues - a bit of a story.
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Old 07-01-2017, 11:17 PM
Aaron31 Aaron31 is online now
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Default D40/YD25 issues - a bit of a story.

Hi all - I thought I would share my recent experience with an engine issues in my D40. I have had it for about a year. It's a 2009 STX (auto) with about 195,000 on the clock.

It had been fine up until cup day weekend. It developed a power surging issue where under load (up a hill) at more than 2500 rpm, there was a noticeable fluctuation in the power with RPM. Basically 2 seconds on and then off. Not off completely, but just less power. Other than that, it was still drivable and smooth at low revs. You could see it on the tacho and feel it in the drive line.

Given there was a very recent creek crossing involved, I went straight to the sensors (MAF and MAP) and cleaned them out with carb cleaner. I also checked the air path for leaks (pipes/intercooler). It actually seemed to smooth out from that point - albeit briefly. Incidentally, there was no evidence of water in the intake.

A lot of reading about power fluctuations led me to the SCV which I swapped out with a new one. It didn't help. In addition I also took the opportunity to change the fuel filter which was overdue. The boost solenoid was in the back of my head but its behaviour led me to think it was a direct result of another signal it was getting (or not) and it was trying to compensate - because it was defiantly doing something. I also noticed that the turbo actuator at idle was going up, and down - curiously, the timing of which was in line with that 2 seconds on and then off.

In amongst all this, I got one of those BT OBD2 jiggers to assist. The first, obvious thing was the MAP pressure - it was all over the shop. Again, I had no solid basis to know what was normal (my first vehicle with a tubo). Knowing that the pressure was supposed to be anything up to 23psi, it was very apparent it was not getting anywhere near that level with any sort consistency - at least according to the ECU which was lucky to get/see more than 6psi. With it running I popped off the air hose before the intercooler and there was without doubt a strong breeze there. I manually actuated it such that the flow basically stopped. This gave me some level of confirmation that the turbo itself was OK. Incidentally, no ECU codes to report.

With all that, the boost control solenoid came into focus. I took it out and literally hosed it out with carb cleaner - and also checked all 3 vacuum hoses and gave them the same treatment with the carb cleaner. All good. Nothing noticeable at all in terms of muck etc. A quick drive yielded a noticeable improvement with a FAR more steady MAP number indicating giving me a glimpse of what I had been missing out on. It was short lived however - the next day say it unable to get more than 6psi going.

But I now had something solid to go on. A couple of calls and $145 Iater, I had a new solenoid and we are good - thankfully! Power is back, and boost is very stable.

I figure that the solenoid was working but it was operating in the 'all' or 'nothing' positions. No variability in between. Looking at the actuator with the new solenoid, its apparent there is a high level of control there. It moves, but it's with far more finesse or subtlety. Based on what I (now) know, my theory is that it was sticky. The ECU would try and adjust it but not get any change/movement and keep feeding more (electric) power/signal to the solenoid until it overcomes that stickiness and goes straight to the full position. Then, it goes to adjust it the other way where the opposite extreme happens.

I have to wonder why a creek crossing (apparently) triggered it. The solenoid itself is sealed - without question. From the connector to the moulded body. There is no way into it. My guess is that the sudden cooling action of the creek water (it was pretty deep) upset it.

The big lesson here: baseline! Spend some time getting to know those performance metrics/numbers so you know what your truck does normally. Get one of those cheapo eBay ODB2 adapters to assist. Things like MAP and MAF numbers, and how they correspond at certain RPM levels. Even how much that turbo actuator moves at idle and also how it sounds. If you can recall those with a high level of confidence you can probably get on track to fixing a glitch a lot quicker.

All this gives me new appreciation for what 'mechanics' have to deal with these days!
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Old 09-01-2017, 08:30 AM
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Boost Control Solenoid is a known "fault" area and as such Nissan always keeps them in stock.

Mine was easy to diangnose, it would suck all the way up, stop, then drop (with a very subtle click noise) and the cycle would repeat. It would go from "no boost" to "over boost" and cycle over and over.

I have found cleaning them with *ANY* cleaner effectively destroys them. Mine went from "suspect" to "seriously dead" after I cleaned it with Contact Cleaner.

The cure here is to remove the BCS all together and put in a DAWES valve setup. No electronics to screw up, just mechanical operation of your boost.

SCV usually show as an idle hunt at cold.
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