EFI relay unplugged

[xubuntu]

I just wanted to jump in because I recently had a very similar experience, where I was having a severe lean condition and rough idle on cold start and stall/sputter/intake backfire on acceleration during cold cycle. Although there were a number of contributing factors the main issues for me was the cold start air valve was sticking. I spent many a frustrating day adjusting the AFM, checking it with a multi-meter, comparing to another I had, swapping it out, without any substantive success. Additionally I continuity tested every sensor, and everything tested within spec. I was pulling my hair out in a troubleshooting session that seemed to go in circles. In the quick read of this thread you and I almost identically followed the same troubleshooting steps.

Then I stumbled upon a very comprehensive “real world” L-tronic troubleshooting site, I found very helpful in truing up all the maladjustments from PO’s, and eventually revealing my root cause.

http://www.hiperformancestore.com/Ljetronic.htm

The entire doc is a good read, but the section “Step 4 The cold start and warm up system” maybe the most relevant to your present problem.

I didn’t take the air valve that serious until I realized how much of a vacuum leak this is intended to create to support cold start, and how slow or sticking operation prolongs a lean condition. When I temporarily capped the line between the AFM boot and the Air Valve there was an immediate improvement. A remarkable difference was made for me when I cleaned and adjusted it (per the link provided). My Z went from un-drivable to drivable immediately. I still have a minor (very short) transition window near warm operation when the valve is still open a little too much, but it resolves in a very short time. I need to adjust it close a little more to get it perfect.

A side note to the value of this guide, I realized how sensitive any air leak is for L-tronic, and as a consequence of following the guide I sealed up previously undetected leaks in the AFM->(Throttle plate boot), and a leak in my new PCV hose I ordered.

I hope this helps

[rcb280z]

xubuntu, I did a very thorough AAR evaluation including the pinching of the air supply hose running to it and there was no change in the way the car idled, unfortunately. Because if that was it I would be happy that I found it.The test results are outlined in post #45. Thanks for the website...will be looking at it next. When I'm done with this issue I want to talk to you about your cs-130 alt. upgrade.

[Captain Obvious]

I recently had a very similar experience, where I was having a severe lean condition and rough idle on cold start and stall/sputter/intake backfire on acceleration during cold cycle. Although there were a number of contributing factors the main issues for me was the cold start air valve was sticking.

xubuntu, It sounds like you (and the guy who wrote that page) are overestimating the power of the AAR. The AAR can not make you run lean. It does not affect mixture.

Ever.

All it does is boost the cold idle RPM's by providing a temporary air path around the throttle body butterfly plate while the engine is warming up so you don't have to sit there with your foot on the gas to keep it running.

There is no difference in operation between pushing down on the gas pedal a tiny bit with your foot and having an open AAR. Unless you push your foot down far enough to open the idle switch on the TPS, then the ECU does not know the difference between your foot and the AAR.

If you are running lean on cold idle, it's not the AAR's fault. It simply cannot do that to you.

[xubuntu]

@rcb280z,

I will admit I didn't read the entire thread (and post 45 was quite a way back), really my post was an affirmation of a point made by FastWoman in post 87. Like I said I underestimated the impact of the AAR, until it was obvious it was the problem. Good to hear it's not related to your current state, I guess I felt a kindship at post 84-85 because I was there. I love my car, but it was not loving me.

You may have already checked this in a previous post (maybe 45 which I will go read)...did you confirm with a multi-meter that closed throttle does close the idle contacts in the TPS? Meaning the TPS could be good, but the throttle plate is not returning to full close. Either the decel dashpot (assuming yours is manual) or the throttle plate set screw (not the idle air screw) being out of adjustment will prevent a full close.

I'm guessing you already checked it.

The CS130 upgrade on the 78 was very easy mostly because the stock alternator was also internally regulated, however I wouldn't expect it to be difficult in most cases since it's only needs 2 wires, and modified bracket. I anticipated needing more current because I'm field testing some driver performance electronics for my company.

@Captian Obvious,

Before resolution, I did think very much the same way you do, and considered the AAR negligible. Than a realization that hit me like a brick, and I changed my opinion. My AAR was stuck wide open, and to your point the AFM would open more due to the increased ingestion of AIR, and raise the fuel mixure....thus "in theory" making it no different that if your foot was on the pedal with throttle plate open. The part I was missing was that the TPS at this point is on the idle contact. Once I open the throttle any amount off the idle switch, the ECM generalizes (not like modern TPS with variable voltage) how much fuel is needed based on which contacts are made in the TPS. The ECM is expecting a margin of air flow based of the known airflow between idle and WOT switches across the throttle plate. The situation in my case was the volume of air was (expected position of throttle plate) + (1/2" dia full open AAR) = significantly more air volume than expected. Since the ECM doesn't have an o2 sensor, it wouldn't know it's getting more air than normal.

Then with more air ingestion, the PO untighted the MAF spring to make the ECM enrichen the mix. This compounded the problem because they were both off spec, the MAF off by a ratio, and the ingestion off by (1/2 dia volume of air).

Wouldn't the MAF compensate since it's measuring the amount of air flow? I would think so....but the reality is, the ECM attempts to reconcile the input of pedal position, and input readings from the MAF in precalculated "expected operating conditions" (meaning air filter clean, no vacuum leaks, AAR open the expected amount, injectors clean, fuel pressure good, etc) and the ECM get's decent precision data from the MAF, but only 3 states from the TPS (idle, non-idle, WOT). Given the disparity in precision between two components that need to be in operational agreement, there is little margin for the unexpeced. Unlike moderm FI systems that have variable TPS, o2 sensors, manifold pressure sensor to calulate and compensate for out of spec devices, leaks, and un-usual environmental conditions.

So after all this I conluded that there is a signifianct difference between the AAR, and simply pressing the pedal. Pressing the pedal takes the ECM out of idle mode (which is intended to be a richer mix compared to non-idle). (page 13, 280z Electronic Fuel Injection, Theory & Troubleshooting)

In my case, once the AAR was corrected every thing else could be adjusted as expected.

For me the proof was in the results, everything worked, and my o2 sensor was reading a balanced mix after.

**warning this is humor and not reccomended**

To give you an idea how out of wack a wide open AAR will make your engine, try bypassing it....and plug the MAF Boot Hose directly to manifold port.

The idle will shoot way up 3K+, and you will most likely not be able to accelerate with out stalling.

**again do not do this**

Despite my initial opinion that I was wasting my time cleaning and adjusting the AAR.........I'm now a believer the AAR can be very significant.

The reason I'm glad I found the site (and shared it), because it is a "real world" guide that takes into account the realites of aging systems (In contrast to the Datsun FSM, which appropriatly was not intended to cover.

[rcb280z]

Ok, before I post everything I did today I need to run something by you all that I think will help solve my issue.

I had hooked up my vacuum gauge, and tach/dwell meter so I could observe rpms and vacuum will running my tests. I just happened to look up at my fuel pressure gauge and noticed the needle dropped suddenly from 28 psi to about 23 psi and then back to 28 psi. This was all while the car is running. I'm now staring at the gauge, things running through my head, and it slowly climbed to 30psi. I thought maybe FPR. I had a new one in my arsenal so I replaced it. It was holding at about 26 psi now, car running. I went over to the fuel return line and pinched it until I got a reading of 32psi and the car idled better. So my question is; if I'm able to increase the fuel pressure and the engine runs better I could have a fuel pump issue correct? Fuel flow through the injectors only changes if the ECU says to right? not because there is an increase in pressure.

Edited February 19, 2012 by rcb280z

[240260280z]

The ECU controls how long an injector is open (time only). The fuel pressure affects how much fuel will flow during that "open time".

You can adjust the AFM or temp sensor to increase the "on time" that an injector is open but if your FPR is not working, then your system may be out of the sweet spot where it is optimized to work. I am not sure how this will affect your cold start problem.

The fact your car ran better with higher fuel pressure seems to indicate it needs more fuel.

[240260280z]

To check your FPR,disconnect the vac. line to it then run the fuel pump. It should read ~36psi with the engine off.

[xubuntu]

Blue is correct to unplug the vacuum line from the FPR to see it it goes up to 36. If you can reach it but are having trouble maintaining 36 psi with return line un-crimped then you have either air in the lines or a flow rate problem. Even a slow flow will eventually get to right pressure if the engine is off or idling but once you are drive down the road that pressure will be difficult to maintain because the supply cannot keep up with the consumption.

I replaced my pump thinking it was bad, only to find out shortly later my pump supply line had pin holes inside the tank. I would purge the air from the fuel line with a tank more than half full, and once the fuel level dropped below half tank the lines were not submerged in gas and started sucking air/fumes then the car would die. It was easy to see the air accumulate because I installed clear G3 filters on the supply side to catch all the sediment still in the tank.

I'm not suggesting you have pin holes like I do, but a plugged filter, debris filled lines, air in the lines, or a weak pump would make it difficult to maintain pressure resulting in a lean condition.

[rcb280z]

Unless there is something wrong with my gauge I only get 30 psi with Blue's test

[rcb280z]

My buddy has a friend with a dyno and he let us use it today. We were able to tune the AFM using the dyno today. Boy was this thing off! We actually dialed it in to CA requirements. It was a little lean for our taste so we richend it slightly and it was running ok after that. We will have to see how it affects the cold start in the morning. Now on to the fuel pressure issue.....

[240260280z]

You may have to go back to the dyno. If you up the FPR 6psi you will go a lil' richer.

Tune the AFM to ~ 16 @ 3000 rpm with a light load if you want to save fuel on the highway. Then check what happens at WOT... Hopefully it will dip to 12-13 range with the TVS kicking in.

[rcb280z]

Ok Blue, will have to try that next weekend. I checked fuel pressure with engine on and as I rev'd the engine it would read 36 to 40 psi. This is good IIRC.