s14 sr20det engine stability

Discussions concerning the M7790 cpu

Moderator: Matt

Posts: 26
Joined: Tue Apr 28, 2009 11:28 am
Location: St Louis, Missouri

s14 sr20det engine stability

Postby sr20truck » Sun Mar 26, 2017 5:47 am

I've dealt with the s13 sr20det variant with great success in the past and feel I have it down pat. This is my first experience with the variable cam variant and we're simply trying to get it stable in factory form. This is a 69F01 ecu. The wiring harness is a WSP and it is in great shape besides the error code 34 I couldn't resolve until I discovered the pigtail was pinned backwards. All set with that now. The car will idle on its factory and freshly cleaned and flowed 370cc injectors rich, displaying -24% rich side on short term fuel trim. We had them flowed to 4 bar just for fun to discover 440cc reported back yet we still run them at 3 bar standard. The long term will achieve -10%, we'll see 12 afr and then it will stall at idle. Giving it gas will result in evening out the trims and once it calms down, it will begin the rich fuel trim again.

Everything here is new, fresh build and a 13091 bosch o2 sensor from a 300zx tt I've used on every sr I've worked on. There are no boost leaks. Idle produces 20 mercury. The real gremlin here is the idle flag flashes at idle and wont stabilize. even the tps voltage hunts between 0.38 and 0.52, no spikes in voltage as it is actuated throughout its range.

We have replaced the ecu with no success, we have replaced the tps sensor with no success. we drove it and it is strong as it should be but idle isn't stable as it should be. that idle flag flashing worries me. any thoughts? I may be overthinking the issue as I'm prone to doing. Slow me down here with some good advice.

o2 doesn't flash back and forth too often, it likes to live at 0.88
idle pulse width is between 2.75 and 3.26
afm voltage 1.410
vtc is new to me, I notice it giving a flag while driving time to time.
engine load doesn't drop below 19 so the first column is not accessed. its always the second.
sometimes it idles at 812rpm, then other times we cant get it to drop below 1150.
iacv cleaned before install

Posts: 79
Joined: Sat Aug 06, 2011 6:59 am

Re: s14 sr20det engine stability

Postby unex » Sun Mar 26, 2017 6:28 am

faulty maf? i have seen faulty maf, which looked working, but it gave wrong voltage

Site Admin
Posts: 8085
Joined: Sun Jan 29, 2006 1:45 am
Location: Adelaide, Australia

Re: s14 sr20det engine stability

Postby Matt » Wed Mar 29, 2017 10:17 am

I've copied Pete to this thread for his input

When seeing engines in transplanted vehicles, the main cause of issues is usually do with with the wiring of the vehicle. The majority of wiring issues are grounding related. Ensure that you have grounding from battery to engine, chassis to engine and ECU grounding to plenum of engine. The engine is the main grounding point in the vehicle (grounding base)

TPS fluctuating in an issue. First place to check is at the TPS itself. You have replaced the TPS sensor, so sounds like it is not the sensor. check the TPS supply voltage is stable 5V (this comes from the ECU) and also check the TPS signal voltage is stable - using a multimeter or even better a scope which will show fluctuations in voltage. If you have a shifting voltage here, then is it the source voltage from the ECU (5V) or the signal. Where does the fluctation start (from the ECU or from the TPS). Are all your signal wires shielded (like in factory configuration)

Also MAF and CAS lines should have shielded signals in the wiring harness you are using. Check this too

O2 feedback (STFT/LTFT) mainly look at this when vehicle is in cruise (not at idle, since some Nissan ECUs do not report correct trims at idle via Nissan consult - this is a Nissan consult implementation issue from what I can see)

Idle light is from the ECU self learning. It should be steady once TPS input voltage is steady. Normally idle position is learnt during cranking and used from after this point. Fluctating TPS input will not help this

If you take a log (stream mode) then check what else if moving after fixing TPS. If the MAF voltage is stable then TP should be stable (coming from MAF voltage after VQ map lookup) and if RPM is stable then injection time should be stable. AFM voltage seems high but if idle is around 1150 then that is a result of high idle.... possibly high due to TPS idle being off

Return to “Type 3/4/5”

Who is online

Users browsing this forum: No registered users and 5 guests