Chasing detonation- have I found the answer?

[madkiwi]

I have been having pinging that puts my 300zx TT into safety boost for a while- I will tell you what has been dealt with (car has JWT Popcharger, JWT ECU with 13.5 psi jets, Stillen catback exhaust, Z1 SMICs)

Up until August 2013 I had been driving for a while with a bad detonation sensor (code 34). Also codes indicated both oxygen sensors were screwed. All replaced. Up until then the engine had been in safety boost all the time, but I just thought my stock boost gauge was inaccurate. Immediately after getting the detonation sensor fixed it would randomly go into safety boost. No codes, and obviously gets reset when the ignition cycles.

So I started looking for causes.

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.

Had the intake smoke-tested. 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 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.

Wondered if I had carbon buildup from running rich and with retarded timing over a long period so I had the Motorvac treatment (top end and valve de-carboning) done August 20th.

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 11+ to 6 psi.

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.

Saturday 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 (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. 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?

Also, and this may be key- whereas before the car would go into safety boost with no discernible pattern, since the boost leaks have all been fixed I know as soon as the engine starts producing maximum boost (over 10 psi) it will go into safety mode. My current theory is the engine is receiving more air than the ecu was expecting, which obviously causes a lean condition. Before the leaks were fixed, perhaps enough pressurized air was bleeding off to make the lean condition a little more random.

Make sense?

I looked up the test procedure for the MAF. I'm not getting an ecu error so the service manual says check for voltage between pin A (or B, depending on which diagram you are looking at, it is the first wire in the connector) on the MAF plug and ground. With engine off but key ON 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? Googling comes up with all sorts of contradictory symptoms.

Thanks,

Mark

[nissanfreak12]

What type of O2 sensors did you replace it with? How is the engine temp? Does it run hot or cold? How are your injectors? Are they the old or new style?

[madkiwi]

Nissan oem oxygen sensors.
Engine runs very well, was having idling issues over the past couple years so pretty much all the hoses have now been replaced. I installed a new air regulator, cleaned the throttle bodies etc etc, finally solved it by replacing the fuel pressure dampener. It was leaking through the diaphragm, smelled the gas when changing the vacuum tube. Also replaced the pressure regulator at the same time.
When I got home yesterday (after all the boosting) temp was 192 degrees.
Injectors were all replaced in 2007 before I purchased the car, by the dealership. The connectors were all replaced last year, along with all the coilpack connectors.
They are the early style.

[nissanfreak12]

Recheck the ohm readings on the injectors. They should read between 10-14 ohm, no more no less. Its possible one could be clogged, not spraying right, spraying too much. Ethanol kills old style injectors fast, usually in a couple of years. Doesn't matter how many miles.

Another thing to check is the CAS. The Pin could be stripped or not setting correctly causing the timing to be all over the place. Especially when driving it.

https://conceptzperformance.com/Cart/de ... hp?II=4589

[madkiwi]

I will check the injectors tomorrow. However, since 2010 when I purchased the car, I have only used ethanol free gas. It is still available in some places (like Montana).

[ThisIsSparTTa]

For $30 off eBay you can grab a Consult to USB adapter. You can use a ECUTalk, a free program, to read all of the sensors, including the MAF (and also pull codes). I think it would be good to know what the ECU actually thinks its reading from the MAF under various conditions.