I have been having pinging that puts my car into safety boost for a while- I will tell you what has been dealt with.

 

I discovered the local Nissan dealer installed completely wrong plugs (PFR5G-11). Put in the right "cold" ones (PFR6B-11B) but that did not solve the detonation problems.

 

I knew I had some serious boost leaks, I got the boost leak tester (with the pressure gauge and the Schrader valve) and was unable to get it to pressurize. Literally the air leaks out as fast as I pump it in.

 

My mechanic smoke-tested, claims he could not find any leaks. I knew this was bs, so I took it to another shop. They found a leak from the vent hole on the LH recirc valve. A lot more smoke was coming from the area that could be explained by a 1.5 mm breather hole, but we could not see any other source.

 

I decided to go over my vacuum lines very carefully, found a leak in the hose to the LH recirc valve (so not just a leak in the valve, but a leak in the vacuum hose to it). Replaced the recirc valve and the signal hose.

 

I had been driving for a while with a faulty detonation sensor (code 34) and wondered if I had carbon buildup from running rich and with retarded timing over a long period (the sensor and both oxygen sensors were replaced August 2013) so I had the Motorvac treatment (top end and valve de-carboning) done recently.

 

After all the fixes I took it out Friday and while boosting it went into safety mode. I actually watched the needle on my Autometer gauge drop from 11ish to 6. Not happy...

 

I checked the timing after I got home. It was about 16-16.5 degrees. I reset it to 14.5-15 degrees. The timing was rock solid, no wiggling around (unlike my Pathfinder, which is all over the place).

 

Brand new fuel filter- installed it at the beginning of August. Checked my CTS at the same time, my wife has no idea I was using the kitchen to boil water for dipping a dirty car part! It was all to spec.

 

Today I hooked up my fuel pressure gauge and zip-tied it to the wiper, then went for a drive.

 

When ignition was off- 40 psi every time (and stayed there for at least 30 minutes while I had lunch).

 

Key on- jumped to 42 psi, then back to 40 when pump shut off.

 

On and idling-vacuum gauge showing -15 inches- 36 psi fuel pressure

Driving -10 inches- 37-38 psi

-5 inches- 40 psi

0- 44 psi

 

Boosting-

+5 psi- 49 psi fuel

+10 psi- 61 psi

 

Got to 11 psi and ecu promptly dropped into safety boost. But at 6 psi I was still getting over 50 psi on the fuel pressure. Basically it appears that under all engine conditions the pump is supplying fuel at 3 bars (43.5 psi) above manifold pressure. In perfect order, in other words.

 

After getting home and removing the FP gauge, I started thinking. I know I am getting fuel. I know I have spark. What if I am getting MORE air than the ecu is expecting, ie the MAF is sending bad intel?

 

I looked up the test procedure for the MAF and if you are not getting an ecu error (I'm not) then apparently you check for voltage between pin A on the MAF plug and ground. With engine off but key in on position it is supposed to be 0.8 V. Mine is 0.44 V. With engine idling, 0.8-1.5 V. Mine is 1.245 V. If out of spec the manual says remove and check the hot wire for breaks or dirt. Removed, inspected (looked good) but got out my MAF cleaner spray and gave it a thorough cleaning. Then let it dry, reinstalled and repeated the test. Same results.

 

Is my MAF sensor bad, and is it under-reporting air mass to the ECU? I am too tired to think, or Google right now, so I am really hoping someone smarter than me knows WTF I am talking about.

 

Thanks,

 

Mark

 

(cross posted to twinturbo.net)

my car was going in to safety boost last year a boost leak was the cause .so if you have leaks you need to sort them first

With a situation like this, if you happy that you've sorted the boost leaks, why not source a good 2nd hand MAF or borrow one and replace to eliminate this as a possibility which of course it certainly is.

This is why it's easier to have it monitored by someone good with Nissans whilst the issue is occurring, ie. A rolling road session. Saves a load of time & money and identifies any problems immediately. A MAF that is outputting a lower reading than the OEM-specified voltage for the corresponding airflow will result in detonation, particularly in the transitional areas of the map (when the car is coming onto boost).

Edited September 7, 201411 yr by Noz

Thanks guys, I believe the boost leaks have all been dealt with, the last thing was my carbon canister which has now been eliminated.

 

lonezedder and Noz- part of my problem is that I live in a smallish city (65,000 people) in a remote area. I know of one other TT in town, and am fairly confident a meeting of the Montana 300zx Owners Club could be comfortably accommodated in a corner booth at Pizza Hut. My mechanic, while very skilled and knowledgeable, does not know that much about the 300zx, and the local Nissan dealer has nobody that old (and they are so bad they installed the wrong spark plugs).

 

Point is I do not have some of the resources available to others. The nearest Z specialists are in Seattle- 500 miles (800 km) away.

 

I will put a request up on all the Z forums that I am a member of and see if someone is prepared to loan-by-mail a known working MAF sensor. Maybe I will get lucky.