EFI relay unplugged

[rcb280z]

Then I think we are good as far as charging volts go. I will measure volts before starting also. Thanks Blue. At least I have something else to look at now.

Bob

[240260280z]

Well this is very elusive and it only occurs for a short time and we seem to have checked all of the directly associated components so now to explore a bit more on the outside.

[FastWoman]

Blue, I could be wrong (wouldn't be the first time), but I suspect the ECU circuitry would be TTL and would therefore run off of a 5V internal voltage. If this is true, I suspect anything over 6 or 7 volts would safely run it.

RCB, you say you have 32 psi fuel pressure and 18.5 in Hg vacuum at idle. These measurements don't agree. Either that, or your fuel pressure is too high. I suspect your gauges aren't quite accurate. IIRC, fuel pressure w/o vacuum should be 36.3, and with a 19 in vacuum (approx 9 psi), that should drop to 27.3 psi. A 4.3 psi drop would correspond to roughly a 9 in Hg vacuum, which perhaps sounds more likely. Anyway, these numbers don't agree.

Have you tried adding resistance to the coolant temp sensor circuit yet?

[240260280z]

Hi S,

I think the EFI system has voltage references across known resistances to compensate for the battery fluctuations and alternator fluctuations on the bus. I know of one in the AFM on the circuit board. There are no 7805 78xx type regulators that I have seen... it appears to be all analogue pulse shaping.

Probably germanium and maybe ECL too..... but that usually requires -V and +GND..... at least there are no tubes.

[rcb280z]

Fastwomen, I have noticed my fuel pressure gauge doesn't give correct readings all the time. Right now it is at 28 psi. So go figure. To adding resistance to the CTS circuit the answer would be no. Not sure I understand it completely. I have read your thread about it but when it comes to electrical I am lost...embarrased to say. Don't get me wrong here, Iwant to try it. Guess I need to read it again. BTW thanks for the input. It's nice to know that everyone has hung in there with me so far.

Blue, I just ran the procedure you suggested. Couldn't wait til the weekend. Ran jumper cables from our altima and sad to say there was no difference. I was hoping it would be something simple. Nothing makes sense! All sensors test good! Dangit! What the heck!

Edited February 24, 2012 by rcb280z

[240260280z]

Well it was a shot.

Another bit of data that seems to be constant is:

- Fuel pressure seems to vary

- This thread started with a fuel pump problem

- Lean, Rich, Normal variations can be caused by intermittent Fuel pump or Fuel Pressure Regulator

Some more things to consider trying:

- replace the small rubber hose from the FPR to the manifold

- power the fuel pump directly with 12V from a 2nd battery at rear wheel, or from long wires run to the car's battery before cold- starting.

- swap out fuel pump

- swap out FPR

[rcb280z]

Blue, I changed out the FPR last weekend with a brand new one. The vacuum line is new as well. I think, not 100% sure, the fuel pressure is varying due to faulty in line fuel pressure gauge. I will purchase a new gauge and if that one shows varying pressure then I will replace the fuel pump. The one that is on the car now is an aftermarket one. I believe it is the Walbro one. Can't remember exactly, it's been about 10 years. Maybe I should find a stock one and replace it with that. I'm grasping at straws now. But that just means there is still hope. Maybe I should install new injectors? Thanks Blue. Have a great day.

[Zed Head]

The inexpensive liquid-filled fuel pressure gauges tend to read incorrectly when hot. I had one that did, mounted on the intake manifold, and it's also referred to on one of the aftermarket FPR suppliers sites -

http://aeromotiveinc.com/2010/01/advanced-tips-for-efi-tuning-with-fuel-pressure/

Where is your gauge mounted?

[FastWoman]

RCB, to wire the potentiometer (also called a variable resistor) in series, you would partially unwrap the EFI harness near the ECU, cut the #13 wire to the ECU plug, and connect in the potentiometer between the two wire ends. I would suggest soldering the connections and then insulating with heat shrink tubing. You can find "how to solder" videos on YouTube. It's easy. As an alternative, you can connect the potentiometer in series with your CTS under the hood (not my favorite installation place). Just connect a male and female bullet connector to the two contacts on the potentiometer (see below), and plug the assembly in series with the bullet connectors on EITHER SIDE of the CTS connector.

As to which two of the three connectors on the potentiometer to wire: You can determine this by trial and error before you ever connect the thing up. Simply adjust the potentiometer to anywhere in the middle of the adjustment range. Then measure the resistance across any pair of connectors on the potentiometer. If you measure 5 kOhm (on a 5 kOhm potentiometer), you have identified the only connector pair that won't work for what you're doing. Pick a different pair. Identify which direction of adjustment INCREASES the resistance across the connectors. This is the direction of adjustment that would make your fuel/air mixture richer. Now adjust the potentiometer's resistance all the way to zero (leanest possible adjustment). You may wire the potentiometer to the clipped wire ends in either direction -- as long as one wire goes to one connector, and one wire goes to the other.

Now insulate it all up, and start your engine. With the potentiometer adjusted to zero, it will run as it did. Now adjusting the potentiometer to higher and higher resistances, you will be richening your mixture. That's it! It's actually very easy.

[rcb280z]

Zed Head, my gauge is mounted after the fuel filter, and before the hard line. I thought about it getting hot and figured this was a good spot. Thanks for the link. Lots of good info there. Oh, I ordered the "dry" fuel pressure gauge. If this one shows inconsistant readings then I will replace fuel pump. FPR is new so it would have to be the pump then.

Fastwomen, when you explain it like that it makes sense for a car with a lean condition. I'm still confused, unless I'm missing something, how this will help an already rich condition. as post #129 explains, I'm already rich with 1.8-2.5% CO's. And high Hydro Carbons. I wish the potentiometer was my answer, unless like I said, Am I missing something? Maybe so. My brain is scrambled eggs right now.

Edited February 25, 2012 by rcb280z

[rcb280z]

Another question for Fastwomen. What's the difference between the potentiometer adjustment and the AFM adjustment. Wouldn't you get the same results for enrichment?

[rcb280z]

UPDATE: On the cold start aspect; when I started the car this morning I let it struggle with the unstable idle...didn't touch the throttle. Took about 3 minutes, seemed like it was searching, but the car actually made it's way to the cold idle range. About 1300 rpms and then slowly dropped to factory setting. OK this is good. I can accept this. On the rich running condition: Experience would tell you that popping through the exhaust means "rich" correct? And popping through the intake means "lean" correct? So what the heck does it mean when you have both? I thought you could only have one or the other. If I hit the throttle it will pop through the AFM occasionally. But it sits there popping through the exhaust like there is an intermittent miss during idle and part throttle. Don't know about full throttle. The plugs are clean as you can see in post #77. Could I have a combustion chamber issue here? I have a friend that had to replace his heads on his chevelle engine because he was having a similar issue. Thoughts?