Topic: **Pics Added**-Engine died, can't get any trouble codes

[scott.475]

My truck up and died on me today, luckily only about a mile from home. It cranks but does not try to fire at all. I put a jumper wire on the terminal block to download codes, but nothing shows at all...I mean the engine light does not come on, period, when I do this. I will check the ECU fuse in the morning, but if that is good, if the ECU has gone completely bad, will this keep the engine light from coming on all together? I wasn't to worried about this initially, but since I can't get any codes I'm starting to get a little frustrated! If I remember right, this light comes on every you start the truck, or even turn the key to "ON", but it is not lighting at all now.

This is for a '91 V6 3Vze, by the way.

[reklund5]

EFI fuse blown?

[scott.475 [OP]]

I just finished checking all of the fuses, and they are all good. I pulled both the EFI and ECU fuses to reset the computer, keep them out for about 30 seconds, and still nothing. The ECU is making a very audible click, almost like the sound of a blinker going a single time, "click-clack", when I turn the key on. I don't know whether it has always done this and I am just noticing it now, or if it is new.  

The search for the cause starts in ernest tomorrow, I really suspect my computer has died though. I forgot to mention in my first post that, when I was driving it today, I did notice that the RPMs were somewhat erratic, not racing, but sure didn't seem normal.  

[Marlin]

Have you checked the larger 40+ amp fuses?
This sounds like a main power supply problem?

Marlin

[gferris5]

all the cars that I've had do that to me turned out just to have bad fuel pumps. Dead ecu's are kinda rare as far as I know. Take a rubber mallet and tap nicely on the fuel tank and see if you can get the fuel pump to stutter to life. Good luck

[gferris5]

oh yeah, I think this also jives with your no-code situation, a dead fuel pump doesn't have a code-correct me if I'm wrong

[scott.475 [OP]]

oh yeah, I think this also jives with your no-code situation, a dead fuel pump doesn't have a code-correct me if I'm wrong

Okay, but, the light isn't coming on at all...period, not even giving me a no code reading, which should be a flashing light every 1/2 second or so. My engine light just isn't coming on at all now, whether I am using a jumper to try and get codes, or just trying to start it. I would think with a dead pump I would still at least get a normal reading?

[scott.475 [OP]]

Okay guys, got it figured out. It was my mass air flow valve. Like someone else here said a few weeks ago, I am more surious than I am smart, which led to the problem.

A couple weeks ago I changed my air filter. I got curious about where my Mass Airflow Sensor was, and started probing around. As you look at the air flow valve from the top, the wiring harness plugs into a terminal that is held in place by two screws. Like an idiot, I tried pulling it out to see what it was. ***WARNING: DO NOT DO THIS!*** I immediately realized my error. Three of the leads had wires connected to them, all the others had nothing. Thinking that they just pushed into place, I replaced the terminal. Little did I know that I had broken the solder points on all the rest of the leads.

So, this morning, figuring the last thing I worked on is probably what is causing the trouble, I tested the valve. The ohm measurement was way below spec. I pulled the cover off (the black thing on top, squared on one side, round on the other) and saw the destruction I had caused. Anyway, I was able to get  everything soldered back in place and put it back into the truck. Turned the key to the on position and saw the engine light come one. It started with no trouble at all. I let it run for an hour, and it did fine, so I think the problem is solved.

[gferris5]

cheap and educational, nice work!

[scott.475 [OP]]

Okay guys, here are the pics

Here is the MAF valve from the top. The black D-shaped thing is the cover for all the internals.

You can see I have cut the silicone off from around it. The screwdriver is pointing to the male end of the plug that you DO NOT want to try to remove!

Taking the cover off.

Be very careful when you cut around the cover with a razor and when you us a tiny screwdriver to pry the cover off. There is a little step that stops you from going too deep, but you could easily push past it if you put too much force behind it.

The internal components

The picture is fuzzy, but the three lines point to the connections that I broke. I broke one off of the circuit board and three midline between the plug and the board. I was able to fix them all. The connection on the left is actually underneath the wire and plug that you see. Also, if you look around the inner wall of the housing you can see 6 vertical posts, which are what the  cover sits on when you replace it. Don't push too hard when you put it back!

[reklund5]

the reason that you didnt get any check engine light and  your engine didn't run is that power runs from the air flow meter to the circuit opening relay that fires up the fuel pump.  It also grounds the ECU.  ( I just did an EFI swap, so this stuff is fresh in my head...) Technically, if you had shorted the fp and b+ terminals, the circuit would have been completed and the truck would've run- even with the MAF unplugged/damaged.  As soon as you crank the truck and the MAF flapper valve opens, the arm on the circuit board swings over and supplys power to the circuit opening relay, that fires up the fuel pump.  The rest of the distance that the arm swings gives the computer a reading on how much air is going into the engine based on the resistance in the circuit.  

Anyway, glad to hear you got it fixed- good work!
Ryan