pezfallout

Okay gents, let me run this one by you:

1993 GXE

Drove car to work, had an injector that was going bad, but would kick on occassionally if car was shut off and cranked up again. Cranked it a few times, injector wasn't coming back on, and left it sitting while I went to work. Came back out to leave, car just turns over but won't fire. Cannot hear the fuel pump spin up.

Here is what I've tested/replaced:

1) Replaced the fuel pump relay, no change.
2) Hotwired the pump (attached the negative terminal lead of the pump to the chassis ground of the pump retainer), it spins up and puts pressure in the system and fills the fuel rails. Motor turns over but won't fire.
3) Removed the safety relay while the pump was hotwired, pump won't turn on, so that relay is good.
4) Pulled a couple of spark plugs, bone dry. There is no fuel going into the cylinders.
5) Went to go check the ECU codes, turn the key into the ON position, nothing. No lights, no nothing.
6) Haynes says the CHECK ENGINE light should light up and remain on if the ECU is receiving power, it's not coming on at all.
7) Something peculiar, but if I turn the ignition switch from off to on the speedo bounces up to like 5-10mph and then falls back down and stays still. Don't know if I've just never noticed it or if it's a sympton of something.

Through all of this it looks like my ECU is dead, though. The negative ground circuit of the pump isn't being completed, therefore it won't turn on and this is controlled by the ECU. As well, the injectors aren't firing.

Can anyone give some insight as to what I can check with the ECU itself to see if it is truly defective or can speak from experience that I'm heading down the right troubleshooting path? I'm going to have to take time off of work to get the Max fixed but I would like to take as little as possible.

If I have to buy a new ECU I would like to get on ebay asap to get one shipped out tomorrow. If anyone can give some insight I would really appreciate it!

Clayton

sleepyvg30e

iTrader: (1)

i doubt the actual ecu itself is somehow damaged ive never heard or read about that happening before....it might be that the ecu just isnt receiving power for some reason

BenStoked

iTrader: (7)

check your fuses?

sonicii

Agreed.. check the ecu is receiving power and has a good ground.. a dead ecu is possible, but it is more likely to be something else.

Niccos89

iTrader: (2)

Will the engine even turn if the ECU has no power?

I'm gonna put my money on inconsistent power to/from ECU.
Are you getting ANY lights on your dash at all? or just no CEL light?

93SCMax

iTrader: (3)

Just a couple of hints:
1) One bad injector will not keep an engine from starting. I've been running with two bad injectors for a while and she starts religiously every time.
2) Have you double checked your battery or alternator. Seems like a lack of voltage to multiple components.
3) Double check ground wires (assuming you have already taken earlier advice and checked all fuses.
Good luck.

pezfallout

Okay, have an update:

The ECU was indeed not being powered up. I proved this by placing a 16ga solid core wire in the ECCS relay pins 1 & 2 to run power directly to the ECU. Fired right up without issue.

However, my idle is constant at between 1000-1200 rpm (it's either one or the other, doesn't really hover between). If I read this picture right...



I swapped out the relay with another one I had but received the same problem of the ECU not powering up, but I replaced the jump and it fired.

The jumper is feeding pins 49 and 59 ("Battery source" and "power supply") of the ECU which is powering it on, but the lack of the relay is not giving voltage to pin 16 (ECM power source).

It's obviously working, but can anyone explain what pin 16 actually does since they all basically say the same thing?

Greeny

iTrader: (43)

Look at the fusible links in the black box under the hood(on the d-side inner fender), they have a small window on the top so you can see if the link is burnt.

pezfallout

Yeah, the fusible links are all good. Nothing was burned up or snapped that was visible through the window, but I will throw a multimeter on them when I go back out to pick it up, today. Having to use one vehicle to go and do troubleshooting then go across town to pick up the wife, just to go all the way back to pick up the car with her is a royal pain. I could have no car at all, though.

jonmandude

iTrader: (1)

I had this same problem about two years ago and went thru the same dilemma trying to find it too. It was the ENG CONT (Ecu Cont. in pic above) relay near the battery. Try that.

pezfallout

Okay, here's what I've done today:

1) Checked the fusible links, all are good.
2) Purchased a new relay, same result. No starting. Just turns over.

Here is how it is currently set up and running:

Red is the copper wire I have in the relay slot with the relay removed.


This leads me to believe that the voltage that is supposed to trip the relay and pass power on to the ECU isn't there, therefore when I hotwire it it is as good as gold.

Anyone have any ideas where to go from here?

internetautomar

iTrader: (30)

have you checked for power and ground at the other 2 pins of the relay?

pezfallout

I have, there's no voltage going across it, which either means the ground is bad or there's no power source. Since the ground is going to pin 16 of the ECU (and the ECU has a common ground, as far as I know) and the ECU itself is power on, I have to assume it is good. This means it isn't receiving power.

I had the electronic manual before I had to wipe and reload, but the site is down now. Does anyone know where the voltage lead for the engine management relay comes from?

BenStoked

iTrader: (7)

fuses? under the dash?

pezfallout

Under dash fuses are good, fusible links are good, relays are good.

I can't find where the "on" voltage for the engine management relay originates because I don't have the service manual anymore and phatg20 is down.

I figure it may come from the ignition switch but I would be playing with fire without a print out to go by. Anyone familiar with this electrical link?

internetautomar

iTrader: (30)

PDFtown ...

are you checking for voltage across or to the relay?

BenStoked

iTrader: (7)

http://www.boredmder.com/FSM/Nissan/Maxima/1994/

Pos. voltage comes almost directly from the battery (short stop thru a fusible link), and then to the ECU.

internetautomar

iTrader: (30)

If I am reading the wiring diagram correctly. Pin 58 on the ECU should have an always on positive, Pin 16 is the ground signal to trigger the ECU relay.

Since I am looking at the wiring diagram, a thought pops into my head. The car uses 2 wires to start. 1 of those wires feeds the ECU, it is only used when starting. I would check that both are triggering. the trigger goes to pin 43 on the ECU, it does have a fuse between the ignition switch and the ECU.

pezfallout

Alright, so I did a little more troubleshooting between rain showers (it hasn't really stopped raining for a few days) and have narrowed it down a bit further, I think.

The fuse that you were referring to was the starter fuse (I found an old phatg20 manual I had backed up) and it is good.

Here is what I have now:



I know that the power coming from the fusible link is good, because when I have the ECU jumpered and I pulled the 25amp fusible link it dies. I don't know what/where the "J/C-3" junction is to test continuity between it and the relay terminal and I think it may be where my break is. Any clues what that is?

Amillyon

What's up pezfallout, I'm going through the same exact thing. I just did an engine swap (JDM) I suspect that my injector harness for 2,4,6 grounded out on something and maybe fried my ECU. I did replace the engine control relay under the hood (The green one) but still no spark. I now have power to the ECU and fuel pump though. I'm getting a code 21 ignition circuit failure from the ECU.

pezfallout

Bad thing is, I'm getting a code 55. I haven't had time to get out and trace everything back because of work and the holidays but I want to get this figured out, soon. Using a jump wire in the relay slot is ghetto and if you forget to take it out the battery will die -- just ask me how I know.

Does anyone know what that J/C-3 junction is (picture in post 19)?

pmohr

iTrader: (26)

Per the FSM:

glenmoormax

iTrader: (13)

I am working on someones 99 and I found the same problem. Someone messed up the emanage tune so after i thought I sorted out the tune, and pulled the plugs to clean them off (black from the bad tune), I put the plugs back in and got no fuel. Threw some starter fluid in 1 cylinder and that cylinder fired.

Fuel pump is priming. Zero fuel. The temporary owner of this car added a crapload of aftermarket grounds and I the car has a parasitic draw on the battery (woot). The car was starting but then after firing up for a few seconds it died and isn't getting fuel anymore.

I will try out some of the things suggested here.

BTW, while its a ghetto fix, cant you just hotwire in "switched" power from the ignition from somewhere else to replace the copper jumper until you find the break (or just stop looking and live with the ghetto fix)?
BTW, good use of tech manuals here! I love my dodge FSM's. I have a hard time with the Nissan digital versions cause PDF's are.....

pmohr

iTrader: (26)

The first thing to check on a 99+ not getting fuel is the NATS system (Especially '99s, they love to fail).

If the security light is on while the engine is cranking, or while the key is in the on position, time to go to the dealer.

pezfallout

Okay, had a chance to get back out there to troubleshoot and this is what I've concluded:



Power is being supplied to all points of the relay as needed, however the relay trip circuit is not being completed. The wire dead-ends into ECU pin 16 but it's not finding a ground.

Does anyone know if pin 16 has it's own ground or uses a common ECU ground? If it doesn't have its own ground then that pin has burned up and there's no way for me to correct it without replacement.

Anyone know?

pmohr

iTrader: (26)

I don't know if it's got it's own specific ground, but have you tried checking all of the ECU grounds yet?

From what I can tell they're pins 10, 20, 50, 60, 107, 108, and 116.

pezfallout

So it's been a few weeks since I last worked on it and decided I was fed up with having to jump/unjump the relay at the beginning and end of each day.

After retracing and ohm-ing the lines, I've determined that the actual wire leading from the relay junction to the ECU is bad. I've been working with network infrastructure for years and one of the things you learn is that cable just doesn't "go bad," but there's a caveat -- human and environmental factors. Either a person broke it or the environment degraded it beyond usefulness. It seems like my multiple restarts in a short period of time may have put too much stress on the 16 year-old wire (years of heating and cooling make things very brittle) and melted it in-line somewhere beyond my view.

So later this week I am going to run a brand new lead directly from the junction box to the ECU and bypass the old wire. I guess the lesson here is not to get tunnel vision and not to immediately disregard a possibility even if it doesn't happen that often. When I get it run I'll make sure to post its success or failure. (Shooting for success!)

pezfallout

Just finished up the new wire patch (all by flashlight, lol) and it was a total success. She is back to running beautifully and I couldn't be happier. Thanks to everyone who posted help and experiences!