Anything else to try before replacing ECM? Help in northern New Mexico?

[MountainBum]

I've got a 94 FJZ that died last weekend. Just shut down like someone turned the key off, no start up and no CEL light. After reading up the FSM and on MUD I went through all the EFI components and they all check out fine, relays, fuses, resistors, etc. Fuel pump runs when hot wired at the diag. port. There's power to the all the fuses, relays, etc. The ECM has power at all the right places from ignition switches and the ECM ground works too. Also, the cel light comes on when hot wired as per FSM. So anything else that could cause the cel light not to come on besides the ECM being bad? I'm totally stuck. Anyone up here around the Santa Fe area that might be willing to let me try their the ECM on my truck? Any help would be greatly appreciated, thanks.

 

[informationjunky]

did you meter all 3 fusible links? Does it turn over or nothing? Do you have spark when you try and crank?

 

[MountainBum]

did you meter all 3 fusible links? Does it turn over or nothing? Do you have spark when you try and crank?

links all putting bat power to main fuse box

it cranks, but no spark, no CEL light at all

FSM says check light, it works, then check ground on ECM, it works, then says try another computer
All EFI/IGN fuses good, all ohm checks on relays check out fine, and the ECM has power at bat, b+, ig, which all come through the relays or fuses. I'm stumped....

 

[informationjunky]

From https://forum.ih8mud.com/80-series-...es-faq-item-recommend-keeping-copy-truck.html

Fusible Links and Relays
Below is a list of fuses and fusible links and relays critical for engine run, this is taken from a 96 LX EWD, should work for 95-97 I would imagine 93/94 would be similar.
There are three fusible links near the positive post of the battery, all three are needed for the engine to start and run, they look just like wires as that is basically what they are, they are intentionality weak wiring that melts with too much current, a blown one may melt in half insulation and all and smoke a lot, or the insulation may just look bubbly and melted on the surface but still look attached, or may look just fine from the outside but be severed inside
The three come from Toyota as a set, all three are replaced at the same time, they are cheap, everyone should have a set in their glove box, and everyone should also carry an assortment of regular blade fuses also,

"Main" Fusible link, critical as it is upstream of the 15A EFI fuse under the hood, you can test this one from the drivers seat by turning on the radio, headlights, ac/heat fan, defrost, stop light, tail lights and telephone, if any of the above work then this fusible link is good,

"AM1" Fusible link, critical as it is upstream of the ignition switch and provides the power for to the starter solenoid, you can check this one from the drivers seat by checking the horn/hazards, dome light, diff locks, rear heat, turn signals, cigarette lighter, or wipers,
If you have the hazard & horn but none of the others check the big 50A AM1 fuse in the under hood fuse box (50A AM1 fuse not to be confused with the AM1 fusible link) Might not be a bad idea to stock a 50A fuse incase the big AM1 fuse blows

"AM2" is probably the most engine centric, it provides power to the ignition switch, the injectors, the igniter, the ignition coil, the distributor, and the alternator control system, if you get the yellow light on the volt meter with “key on engine off” this fusible link is good,

 

[SeanAndHis80]

Hey - This is just an outside chance. I just fixed a P0305 thanks to another member in the forum. The issue was that next to the connector for the ECM the wire loom passed through an opening in the frame of the dash. In my case it was the #5 injector wire which rubbed through the insulation and grounded but there were a bunch more wires that were rubbing. I repaired the insulation and added some conduit to the loom of wires as it comes through the dash frame to fix. HTH

 

[jonheld]

The ECM has power at all the right places from ignition switches and the ECM ground works too. Also, the cel light comes on when hot wired as per FSM.

Please be more descriptive when you say hot wired. Are you simply grounding a pin on the ecu to illuminate the CEL?

Have you tested the EFI relay logic? Is the EFI relay closing?

 

[MountainBum]

Thanks. All the links are fine, all putting power to the fuse box, fuse box putting power to the inside fuse box and ignition switch, ignition switch putting power to the ECM.

I guess I'll start pulling the wiring harness even though it seems fine. All the points on the ECM are getting power where they are supposed to and the ground is working fine. I can't find anywhere that power or ground should be that they are not there. I can't pull any codes as the CEL light isn't working through the ECM, although it does work when hot wired. I'm pretty sure my ECM went. I'm going to start a full FSM ECM wiring check, although the truck won't start, so I'm pretty screwed on those checks. This is driving me f'n nuts, I hate electrical gremlins....

 

[MountainBum]

Please be more descriptive when you say hot wired. Are you simply grounding a pin on the ecu to illuminate the CEL?

Have you tested the EFI relay logic? Is the EFI relay closing?

FSM says ground pin "W" on the ECM to manually light up the CEL to check the blub. It lights up when "W" in grounded so it's not the blub.

The EFI relay puts positive power to pins "B1", "B", and "M-REL" on the ECM when charged according to the FSM. When the key is in the "on" positon, all the efi relays click and B1, B, and M-REL all have positive power. So I can assume the relay is working properly. Also, the relay ohm checks come out fine. I'm ready to just push this f'n truck off the end of my driveway and claim it on the insurance

 

[jonheld]

MREL energizes the coil in the EFI relay.
B+ and B1+ are simply tallies to the ECU to say that the EFI relay is closed as well as supply power.
The EFI relay supplies power to the ISC valve, VSV valves and a host of other items that all talk to the ECU.

Certainly swapping the ECU for a known good one is a good and quick diagnostic, but I would still explore other options if one is not available.

 

[Pin_Head]

The EFI relay is a known weak point and looking at voltages on an open circuit (like the EFI relay when it is not running) can fool you if the resistance across the relay contacts is too high for it to run the EFI solenoids. The pick and pull is full of toyota EFI relays, so having an extra one to check won't set you back much and you can always use a spare.

 

[MountainBum]

The EFI relay is a known weak point and looking at voltages on an open circuit (like the EFI relay when it is not running) can fool you if the resistance across the relay contacts is too high for it to run the EFI solenoids. The pick and pull is full of toyota EFI relays, so having an extra one to check won't set you back much and you can always use a spare.

I picked up a brand new EFI relay and tried it. NO change. I did however check the coil, and its primary resistance is reading 1.1 ohms, higher than it should be, so I'm going to try a new coil, but I doubt that is the problem. We'll see.

 

[krenzzfj80]

Reach a verdict? Same problem right now.

 

[MountainBum]

Nothing yet, haven't started the more odd ball tests. I did read up a thread about one guy having pulled his MAF plug and it fried his ECM and MAF when it didn't get put back in right. So that will be my next check. Also will be checking the tps, vsv, egr valve and a few other things from the SFI trouble shooting section of the FSM. PM me if you don't have that and I can email to you. It's 20 pages of component/ECM voltage checks and it seems like any of them could cause the CEL light not come up, but the ECM still could be good. Almost seems like it would be much easier if it was a simple ECM replacement as they are only 150-200 on ebay for a used unit.

 

[MountainBum]

After inspecting and testing a bunch of other components, I found my wiring harness brunt through at the egr pipe. I will be pulling it and checking the wires but it looks like I probably have a torched wire or 2. This seems to go along with a lot of other threads about no cel light.

 

[landtank]

check the alternator connections and pull the brush pack to check their length. No alt output no start but it will crank all day.

 

[MountainBum]

ECM is toast

check the alternator connections and pull the brush pack to check their length. No alt output no start but it will crank all day.

Thanks, check'd it.

My ECM is blown, or at least the 12V to 5V transformer part of it. It isn't putting the 5V power to the VAF and TP sensors so the ECM isn't getting any feedback on them. No voltage back to the ECM = no start. Well at least I know my way around the ECM wiring now.

I think this is pretty rare. But for anyone else having no start issues, check the VCC pin on the ECM for 5V + power with ignition in on position. If you don't have it, ECM is toast.

 

[landtank]

when you checked that 5V did you remove all those outputs from the ECM to be sure you weren't seeing a short to ground on that line?

 

[MountainBum]

when you checked that 5V did you remove all those outputs from the ECM to be sure you weren't seeing a short to ground on that line?

No, but I guess I will to check. The VAF and TP sensors checked out when I did a resistance test on them and all my wires checked out fine under the burnt crap covering the wires. I was also going to unplug the ECM and sensors and run straight power through the all the lines from the TP and VAF just to make sure they aren't grounding out. Everything I've checked still points to a blown ECM.

 

[busmup808]

You got mail!

 

[landtank]

No, but I guess I will to check. The VAF and TP sensors checked out when I did a resistance test on them and all my wires checked out fine under the burnt crap covering the wires. I was also going to unplug the ECM and sensors and run straight power through the all the lines from the TP and VAF just to make sure they aren't grounding out. Everything I've checked still points to a blown ECM.

it's a technique that I use when in these situations. A short in the wiring will pull down 5vdc pretty easy and likely do no damage to any components.

If you unplug the 5vdc lines from the ecm and the 5 volts is back you simple plug one line in at a time until it's gone again and that is you bad line.