Still runs rich!!

[mjr45]

Today driving it ran fine, but still rich (exhaust smells like fuel). The tach is not jumping around and reads steady, that's what is so puzzling about this car, one its fine and the next day it isn't. All I did today prior to driving was do the checks as above and make a minor adjustment to the TPS.

[Zed Head]

Well, so much for my approach then. Maybe you have a problem on top of a problem.

When it is "running fine" except for the rich mixture, it would tell you a lot if you could measure fuel pressure while driving. It should be high 20s to low 30s when cruising and jump to 36 when you give it throttle.

I had a really tough time diagnosing a similar problem with my 1976 engine because the FPR caused the pressure to rise out of spec. high only when the regulator got hot. I didn't like disconnecting the fuel lines to connect the regulator on a hot engine so I only measured pressure when things were cooled off. I'm not saying that's your problem, but measuring fuel pressure while the problem is happening will at least let you know if fuel pressure is right or not. If it's right then you can move on to looking at other things.

[mjr45]

Yep kinda came to same conclusion, I'm trying to figure a way to put a fuel pressure gauge in the cockpit. I may also put in a new FPR, which I have a gut feeling is part of the problem. Thanks for all the help.

[Wade Nelson]

Borrow someone else's vacuum gauge and see if yours and his match readings.

Then spend 10 minutes on this website, learning how to read it, and decide which of these 12 scenarios match

what you're seeing.

http://www.secondchancegarage.com/public/186.cfm

[mjr45]

Wade, if its true that for an increase in altitude 1000'=1" drop in pressure from sea level, then my vacuum reading would be 21" since I live at 9000' altitude. Does that make sense? Thanks for the link.

[Wade Nelson]

The 280ZX's sold in places like Denver had a special "altitude compensator" that tied into the ECM to lean that sucker out when it sensed it was above 5000'.

I don't know if the 280Z's did or not.

It was a little barometric switch that connected to two leads on the ECM. It's shown on the wiring diagram. Apparently it was mounted up under the dash.

You might do some research, find out if your model COULD have been equipped with this doo-dad, and if so, figure out whether shorting those two wires together, inserting a resistor, whatever, could be used to simulate that switch tripping and saying "Yes, I'm at high altitude, and need to lean things out"

With an oscilloscope attached to one of the injectors, you could simply watch and see if the injection pulse gets shortened when those leads are connected, etc. with the motor held at a fixed rpm.

I would probably start by shorting them through a 10K resistor, then 5k, 1k, 500, etc until I saw some effect. Or else FIND a car so equipped, pull the compensator out and measure it with a DVOM to see how to "fake it."

[mjr45]

I don't believe my Z has the "altitude compensator", but there are 2 wires that hanging loose next to the ECU, I have wondered what they are for since ther doesn't seem to be any connection for them. Unfortunately, I don't have access to an oscilloscope. Thanks for the help.

[darom]

My 76 has the same 2 wires (white) next to the ECU.

Do you have car junk yards around where you can get a used FPR just to run a quick test? The new ones are about $50. Or check the hybridz.org's 'Classifieds' section - I usually have good luck finding used parts there.

[mjr45]

I ordered a new FPR yesterday, so we'll see if that makes any difference. Z's are non existant in bone yards around here. Does anyone know for sure what those 2 white wires are for? I can't seem to locate them on the wiring diagrams, but maybe I'm not looking in the right place. Yesterday after driving up the mountain, I stopped for a few minutes and when started it ran rough was coughing acting like it wasn't getting fuel and spluttering for about 90 secs then ran OK.

Edited September 21, 2012 by mjr45

[Darrel]

Check to make sure the temp sensor and temp sending unit wires are not switched.

[mjr45]

Already did, the temp sensor has a 2 wire connector and the temp sender is a single wire, I even switched the thermotine and temp sensor wires to make sure I hadn't put them on the wrong sensors, I hadn't, it ran like crap with switched wires.-

[grantf]

I have only skimmed this thread so sorry in advance if it's already been looked at. Have you tried disconnecting and plugging the cold start injector?

Edited September 24, 2012 by grantf