No Start! Engine is getting spark and fuel, fried ECU?

So I was poking around in my fuse box, put it back together. No Start. All i did that day was pull some wires through the firewall including a 4awg power cable, i also am putting two 16awg wires into the fuse box for future fused switches.

All relevant relays are working (EFI, starter, circuit opening/fuel pump), fuel pump is working, spark test shows coils are firing on crank, fuel is getting to rail, fuses look good.

I need to get a noid light to check injectors. A multimeter isnt showing anything.

I have a RS3000 alarm, but the wiring diagrams show this would disable the starter. Starter is cranking.

I cant connect to the ECU with an OBD scanner.

I dropped off the ECU at a module repair shop this morning for diagnostics. Well see what they say.

Im looking at the wiring diagrams, trying to trace ignition cables. Found this plug under the steering column, with a loose grey wire (i assume the grey wire is the alarm antenna).

 

Wow no one???

I went back to the repair shop. The guy found a micro capacitor on the back of the board that was blown off. He said it looked more from physical impact then overloading. All the fuses and diodes tested good. Other than that there were the main processors, that he couldn't test.

I got home, picked up a noid test kit. The injectors are pulsing, so the engine is getting fuel. The spark plugs are sparking. It just keeps cranking though.

Ive been using the following guides in testing the circuity. There is not a pin guide for 3RZ available online. The FSM found here and other places are only for the 5VZ engine.

I found the pin guide is accurate for the plugs themselves. But in referencing the engine control diagram for the 3RZ: E5=A, E6=B, E7=C, E8=D.

 

The area you pulled the new wires through the firewall, were there factory wires in the same hole? If so maybe check for pinched wires?

Is the new wiring connected to anything yet?

 

FWIW that loose connector under your steering column is the same one I have. Someone told me that it is for the ignition ring light (that some of our trucks came with) but mine tested hot all the time.

 

Ok, i can add that i can now connect to the ECU via my OBD scanner, though as its being reset constantly, there are no codes.


I am getting cranking RPM from the scanner, so crank position sensor is working. Throttle position shows around 11% at rest. Too high?

Vacuum gauge shows 10-15 psi fluctuating during cranking, none pre throttle.

The large cable is B+ for the amp under the seat. The other two are not connected to anything. This all started after i opened up the fuse box, though ive checked all the relevant circuits in the fuse box. Im dreading having to go through there again, but i will be tomorrow. I was concerned that the magnetic field from a 4AWG wire running parallel might have an effect, but i had it unplugged with no change.

Thanks, i figure it was for something relating to a column shifter version. Makes me nervous when i see lots of loose connectors.

 

That sucks, hope you find it. You have all the required ingredients to make combustion. Hopefully it's something simple.

I have lots of loose connectors, under dash, under hood, I only worry if there is another near by that fits it.

 

Your injectors were pulsing but do you have fuel pressure? My guess is no fuel. Spray some carb cleaner in the throttle body and see if it fires a time or two off the fumes.

 

There is fuel pressure. The pump is working and there is fuel getting to the rail. I don't have the attachment to hook my gauge up to the fuel line, but i disconnected it and routed it into a bucket while cranking, it was pumping.

 

OK, i was just fooling around with it, and I discovered i was able to get the truck to start by holding the throttle open during cranking.

The truck will not idle at all, as soon as i let go of the throttle, the car dies.

 

Sounds like Idle Air Control Valve? I had one go bad on a Ford Explorer - exact same symptoms. I pulled the one on the Ford, sprayed it good with carb cleaner and it was back in business. YMMV. Let us know what you come up with. Best wishes.

 

I agree with arifleman. The IAC is what keeps the engine running while you are idling.

 

Looks like the entire circuit is passed though the ECU. I won't have time to work on it for the next few days, but I pray the IAC is bad. If it passes testing then it's the ECU that needs replacement.

Im not one that automatically replaces parts, i.e. my car is getting bad mileage, lets replace a o2 sensor. In making love to my multimeter the last few days it was purely a fluke that i got the engine to start with a box leaning against the gas pedal.

Again i pray its the IAC that coincidentally blew out during my work, as in reading the diagnostic flow charts in the the FSM, i would have NEVER been directed to looking at the IAC. The FSM, for the 5VZ engine at least, would direct me to replace the ECU first.

This may be the case still, as like i said the IAC circuit is exclusive to the ECU.

 

I'll read from beginning in a few. just getting home from work.

 

Just noticed in reading the FSM, the IAC circuit passes through the main engine cowl wire loom, into junction IF2. Right next to where i pulled the big ass power cable.

I used a liberal amount of 3M strip caulk to seal this all nicely, i dont want to go pulling it all apart. Will see what i can do tomorrow if i have time.

How often do you read of these going out on our trucks? Seems very coincidental.

 

This was my thought too, that maybe a plug or wire was dislodged when you pulled the new wire thru the firewall.

 

So in looking at the various guides out there. The 1996 guide while having a 3RZ section, refers to both leads going to the ECU. This is also the case of the 5VZ guide. The 2003 guide best fits what you should follow, depicting the one lead to the ECU, and one grounding out.



Here are some test probes i made, some are just wire ends i soldered, some are fork connectors bent to form one pin. Also some with 6.3mm spade terminals that can fit multimeter leads, some have 2.8mm spade terminals that fit ECU pins. The longer ones are about 6 feet long so i can go from any plug in the engine compartment into the cab.



I want to make sure the circuit from the IAC plug to ECU is good first. The center plug should be B+ via the EFI and fuel pump relay, thats good with voltage as well as continuity back to battery.




Tested continuity from IAC plug back to ECU pin 6 on plug D (black/red wire), then tested that pin 15 on that plug has continuity to ground (white/black wire). I plugged the IAC back into the harness, and was able to get B+ voltage at pin 6.




So the circuits from the IAC to ECU are good.

 

I found conflicting designs on the IAC depending on which version of the FSM you look like. The 1996 manual for the 3RZ shows the IAC as having both opening and closing circuits. As does the 5VZ from 2000. One side opens, one side closes. The most accurate is the 2003 manual for the 3RZ, though this seems to cause the valve to close when grounded only.




I took off the IAC, and applied B+ to the center pin. The upper pin, RSD, when applying ground, causes the IAC to open then close rapidly.

The default looks to be in the open position, i can see light passing through with a flashlight.

Grounding the other pin has no effect. Grounding the bottom pin, and applying voltage to the top pin has the same effect, the valve opens and closes rapidly, but will not stay closed.



Checked continuity. The top pin (RSD) has 61000 ohms. There is no continuity on the lower pin. What do you all think?

 

BUMP for a thread that does not involve a lift kit or 35in tires.

 

Guess what!

 

Car is running beautifully now. It was the IAC. I was thinking the fucker was so caked with carbon buildups that it would not move until i removed it from the throttle body, but there may have been a different issue.

Note that when i tested the solenoid on the old valve. The control side showed 61k ohms, the ground side had no continuity.

I tested the new one... Control side showed 25k ohms, the ground side showed 9k ohms.





So it may have been the crap sealing the old IAC, or maybe some crap got in the solenoid and killed the ground. Either way its working.

I also seafoamed the shit out of the intake and throttle body, after a good scrubbing. the throttle body looks as good as new.