Intermittent problem getting power to my ECU. Need some ideas.

[B Legit]

So since the beginning of November, I have been having an intermittent condition where I go to start my truck and it cranks strongly but fails to start. The first time that it happened, I popped the hood, fiddled with the fusible links, and pulled the EFI main relay to check the terminal connections. I put everything back and she started right up. I immediately attributed the problem to either the brittle old fusible link or the EFI Main Relay starting to go south, since those were the only two components that I messed with at that time and it immediately started up after my checking them. Installed the new parts and kept the old as spares and the condition seemed to be gone. Recently, the problem has resurfaced and has gotten to be more frequent, (has happened a few times this week.) Each time I have been able to just turn the key to the off position and retry and after a few attempts just like this it always catches and starts right up. I have been searching like crazy and noticed a few different instances where people have noted that when you turn the key to the on position, and the CEL icon is not displayed, it indicates a condition where your ECU is not receiving power, or does not see a complete power circuit (+12v or ground), and that a similar condition to what I have been experiencing is seen. After reading this, I decided to start watching to see if I had a CEL icon during a failure to start condition. This morning when I got in my truck to run some errands, I turned the key to the on position and sure enough, there was no CEL icon , only the seatbelt warning and ABS lights were illuminated. I went to start the truck and it cranked over strongly but did not start. I went through the same old routine of turning the key to the off position, and then back to on to check for the CEL icon. On my third or fourth try, the CEL icon came up along with the AT temp, Low Oil indicator, and the truck started right up with no hesitation at all.

I have done alot of work to this truck in the last 6 months:
In july I swapped in a lower mileage engine as well as a new radiator. Wiring harness was checked near the EGR and looked fine. I also added a digital coolant temp gauge powered off of the Cig lighter circuit.
In August, I replace a few of the low pressure steering lines as well as the reservoir due to leaks.
In September, I welded and installed a 4x4 Labs rear bumper, The Battery was Disconnected at the + and - side while all welding on the truck was done.
In October, I got the three ECU codes of death and replaced my old 1993 era ECU with the updated ECU from a 94 truck.

Since this condition started happening after the replacement of the ECU, I am thinking that I have an intermittent connection in the power supply circuit to the ECU. The thing that has me wondering is that this condition only happens when attempting to start the truck. It has never died on me while driving and has never ran rough or done anything outside of the ordinary while driving the truck and in my searching here on mud, all of the other times these problems have popped up while operating the vehicle. The truck suddenly dies, and when attempting to start it is noticed that there is no CEL icon with the key in the on position. It also seems likely that a loose connection or intermittent connection would be much more likely to rear it's head while in motion or subjected to the movement of the vehicle or engine. In my case it only pops up when trying to start the vehicle. I have not gone through the electrical wiring diagram yet as I wanted to see if anyone here would be able to chime in and help me out with some ideas. Hopefully my description was detailed enough.
Oh yeah, My truck is a 1993 with a 1fz-fe.

 

[CycloSteve]

My first guess based on your description would be to check that all of the engine harness ground wires are properly attached to their grounding points on the chassis/frame (the clusters of brown wires/eyelets). I would also check the DS kick-panel for the same, and be sure that all is kosher in there (ie no water intrusion). Perhaps one of these grounds is loose, or has a bit of corrosion. Worth checking, and should not take too long.



Steve

 

[jonheld]

In October, I got the three ECU codes of death and replaced my old 1993 era ECU with the updated ECU from a 94 truck.

What does this mean?

 

[Ohiofj80]

Had same issue with my truck. Was a few ground wires

 

[-Spike-]

Sounds like the fusible links, if you haven't already re-checked those I'd do that. I had this problem once, the links tested fine, but eventually I found the bad connection was the crimp connector from them to the battery.

 

[B Legit]

What does this mean?

On the 1993 era 1fz trucks, the ECU module is a known problem, so much so that Toyota updated it with a new part for the next year. If you get the codes 83,84, and 85 simultaneously, it means that your ECU is sending erroneous signal and having communication issues, the FSM as well as research and advice here, have pointed to replacing your 1993 era ECU with the updated and improved part number that was put in 94 trucks. I received these codes and attempted to reset multiple times only to have them return. I sourced a used updated ECU (new one is 1400.00 from Toyota) and the codes were gone. It also improved some various random conditions within my truck including off kilter shift points and things like that.

 

[B Legit]

Had same issue with my truck. Was a few ground wires

Which one's? I had the same issue this morning when first trying to start my truck. For trouble shooting purposes, the first thing I did was give the fuse panel right by my left knee a few little bumps and sure enough, the CEL indicator came back and the truck started right up. I feel like I am narrowing this down. I looked inside that panel and there are a few fuses that have to do with the ECU so I will try to dig into that on Friday when I have some time and daylight.

 

[B Legit]

Sounds like the fusible links, if you haven't already re-checked those I'd do that. I had this problem once, the links tested fine, but eventually I found the bad connection was the crimp connector from them to the battery.

I just replaced them at at the beginning of November, but will check all connections. I agree that this would make sense, but the fact that I saw the condition before I replaced the fusible links, and after, leads me to think that the problem lies elsewhere.

 

[jonheld]

On the 1993 era 1fz trucks, the ECU module is a known problem, so much so that Toyota updated it with a new part for the next year.

Interesting. In all the time I've been on MUD I've never heard that before. The ECU has always been known as one of the more robust items with very low failure rates.

In any case, it should be easy to localize the problem during the next "no CE light" event. The ECU fires the EFI relay once it's logic is satisfied. The CE light illuminates when the EFI relay is closed and the ECU is seeing "all systems go".
If your CE light is not on, you need to determine if the ECU is sending the proper logic to fire the EFI relay. That would be a +12 at pin 3 of the relay along with a good ground on pin 1.

While my experience is with the 3FE motor, all 80 Series use the same relay so the logic is identical. You should also be getting a constant +12 in the fusebox on the phillips head screw in the center of the box. That's the +12 feed from one of the fusible links.

If the ECU is not firing the EFI relay, then we need to get more involved with the individual pins on the ECU chassis.

 

[B Legit]

Interesting. In all the time I've been on MUD I've never heard that before. The ECU has always been known as one of the more robust items with very low failure rates.

I believe that the problem is unique to the 93 which seems likely as it was the first year of the 1fz in the US. I was fairly surprised myself when I started researching the three codes that suddenly popped up. Thanks for your input as well, I was hoping that you would chime in. I keep a meter in my truck and will check those two pins underneath the EFI Relay the next time the condition appears and report what I find.

 

[landtank]

Alternator issues can give you this problem. I'd replace the brush assembly and make sure all the connections on the Alternator are clean and tight.

 

[B Legit]

Alternator issues can give you this problem. I'd replace the brush assembly and make sure all the connections on the Alternator are clean and tight.

Hmm, I did the brushes when I did my HG a year ago, but I did have a nasty power steering leak and that could have easily made it's way onto the alternator since it is directly below the reservoir. I will check those connections as well.

 

[B Legit]

Thought I would update with what I did today and how it worked out. I feel fairly confident in what I found, and fixed, but only time will tell if My problem is resolved. First thing I did was go through the lower dash panel fuse block and remove fuses to see if I could duplicate the condition that I was seeing consistently on my truck. When I removed the 7.5 amp ignition fuse it was the exact condition that I have been seeing. Very Promising. I checked the fuse and it tested out well but on further inspection I noticed that one of the terminals was loose. I proceeded to tear the lower dash apart and check everything else and conduct some random electrical tests to make sure everything else was in order. I made some comparisons with my buddy's pristine 95 and everything checked out. I sured up both wires that hit the ignition fuse and re supported the wire trunk line to alleviate any pressure or tension that could be applied on that wire set and buttoned everything up with a new fuse for good measure. Since My battery was unplugged, the ECU needed a few run cycles and a warm up in order to re calibrate. I also adjusted the timing to 5 degrees btdc as it was sitting at 0. Factory says to set it at 3 but I have found that a few degrees past that works well. All in all, I went through about 15 or 20 starting cycles without the issue coming up again. I will update if anything changes. So far, so good.

 

[samfurniss]

what did it end up being i see this is a old post but i’m having the same issue

 

[clx16]

Well this is often related to bad grounds to ECU that get worse with heat etc or the tabs holding a fuse are loose or have green crusty boogers on them. Clean and tighten them as needed. You can check the ecu Pin-out and check the voltages for ground and positive to see if those are good while you are having the indicated problem.