Has spark at the plugs but won't start (1 Viewer)

[alwaysmonday]

1996 Land Cruiser, 175k miles

Driving it this morning. 10 minutes from home while gently accelerating from a stop sign the engine died (it all happened smoothly and did not hiccup or backfire). I tried to start it again and it fired for less than 1 second only 1 time but died again instantly. I tied to start it many more times but it would not fire. No heavy smell of gasoline. Cranks freely but won't fire. Towed it home.

Checked the following items this evening.
Battery is at 12+ volts
I can hear the fuel pump re-prime after cranking the engine over
Fusible link has continuity on all 3 legs.
All fuses appear to be fine.
Confirmed spark at the plugs by removing plugs 1&2 grounding them against the throttle body while cranking the engine.
Plugs look dry
No heavy smell of gasoline from the engine compartment after cranking the engine for 15 seconds with plugs 1&2 pulled from the head
Engine turns over freely
Rotor spins in the distributor cap when cranked over (I believe this confirms the timing chain is intact)
It will not start (or even fire) while spraying starting fluid into the throttle body (this makes me think it may be a weak spark. How would I diagnose a weak spark?)
Scan Gauge shows throttle positioning sensor reading around 8 at zero throttle and around 70 at full throttle.

I'd love some guidance from the Fourm on what to diagnose next and the process of doing said diagnostics.

 

[BILT4ME]

1996 Land Cruiser, 175k miles

Driving it this morning. 10 minutes from home while gently accelerating from a stop sign the engine died (it all happened smoothly and did not hiccup or backfire). I tried to start it again and it fired for less than 1 second only 1 time but died again instantly. I tied to start it many more times but it would not fire. No heavy smell of gasoline. Cranks freely but won't fire. Towed it home.

Checked the following items this evening.
Battery is at 12+ volts
I can hear the fuel pump re-prime after cranking the engine over
Fusible link has continuity on all 3 legs.
All fuses appear to be fine.
Confirmed spark at the plugs by removing plugs 1&2 grounding them against the throttle body while cranking the engine.
Plugs look dry
No heavy smell of gasoline from the engine compartment after cranking the engine for 15 seconds with plugs 1&2 pulled from the head
Engine turns over freely
Rotor spins in the distributor cap when cranked over (I believe this confirms the timing chain is intact)
It will not start (or even fire) while spraying starting fluid into the throttle body (this makes me think it may be a weak spark. How would I diagnose a weak spark?)
Scan Gauge shows throttle positioning sensor reading around 8 at zero throttle and around 70 at full throttle.

I'd love some guidance from the Fourm on what to diagnose next and the process of doing said diagnostics.

If you disconnect the tube to the throttle body then the MAF won't see airflow and won't let it run.

Hook the hose back up and spray it into the filter lid bottom.

Do you have a CEL with the key in the RUN position?

 

[alwaysmonday]

If you disconnect the tube to the throttle body then the MAF won't see airflow and won't let it run.

Hook the hose back up and spray it into the filter lid bottom.

Do you have a CEL with the key in the RUN position?

Good point on the MAF. I did try spraying it into the rubber air inlet tube immediately downstream of the air filter and still no fire.

Yes the CEL is on when the ignition is in the RUN position.

 

[alwaysmonday]

1996 Land Cruiser, 175k miles

Driving it this morning. 10 minutes from home while gently accelerating from a stop sign the engine died (it all happened smoothly and did not hiccup or backfire). I tried to start it again and it fired for less than 1 second only 1 time but died again instantly. I tied to start it many more times but it would not fire. No heavy smell of gasoline. Cranks freely but won't fire. Towed it home.

Checked the following items this evening.
Battery is at 12+ volts
I can hear the fuel pump re-prime after cranking the engine over
Fusible link has continuity on all 3 legs.
All fuses appear to be fine.
Confirmed spark at the plugs by removing plugs 1&2 grounding them against the throttle body while cranking the engine.
Plugs look dry
No heavy smell of gasoline from the engine compartment after cranking the engine for 15 seconds with plugs 1&2 pulled from the head
Engine turns over freely
Rotor spins in the distributor cap when cranked over (I believe this confirms the timing chain is intact)
It will not start (or even fire) while spraying starting fluid into the throttle body (this makes me think it may be a weak spark. How would I diagnose a weak spark?)
Scan Gauge shows throttle positioning sensor reading around 8 at zero throttle and around 70 at full throttle.

I'd love some guidance from the Fourm on what to diagnose next and the process of doing said diagnostics.

Forgot to mention this in the original post.

EGR has been deleted. It had been deleated before I purchased the vehicle. I have put 7,000 miles on it since purchase with no issue. I don't think rhat this is EGR related but figured it cannot hurt to mention it.

 

[Rusty Marlin]

When cranking over, listen for the fuel injectors to click with a stethascope probe (long screwdriver pressed to ear works too).

 

[alwaysmonday]

When cranking over, listen for the fuel injectors to click with a stethascope probe (long screwdriver pressed to ear works too).

I'm willing to try this. Can you tell me if the engine should run on starting fluid even if the injectors are not firing?

 

[Malleus]

No, it won't. I know, not really helpful.

Try this: the engine problem matrix says two things to check -
1) ECM power source circuit (attached)

2) the fuel pressure control circuit (attached) (ignore the Toyota tester stuff - you don't have one anyway). And then check the fuel pressure regulator.

The FSM has the full engine troubleshooting guide. If you don't have it, get it. It's in the Resources section. (say thank you to Marshall)

You can verify the current at the injectors by connecting the harness, at the connector, to your multimeter while cranking.

 

[alwaysmonday]

No, it won't. I know, not really helpful.

Try this: the engine problem matrix says two things to check -
1) ECM power source circuit (attached)

2) the fuel pressure control circuit (attached) (ignore the Toyota tester stuff - you don't have one anyway). And then check the fuel pressure regulator.

The FSM has the full engine troubleshooting guide. If you don't have it, get it. It's in the Resources section. (say thank you to Marshall)

You can verify the current at the injectors by connecting the harness, at the connector, to your multimeter while cranking.

Update: Momentary hope but no progress on finding the issue yet.

The truck started on Friday night after messing around with the EFI relay in the fuse box on the LF inner fender. It started right up and ran smooth for 10 minutes. I turned it around carefully in the driveway and prepared to drive up an incline in the driveway leading from my shop to the main house and it died. I could not get it to start again. I switched out the relay again but it would not start. I have tested all the available relays as defined in EG-331 Step 8 and all passed so I do not think it was the relay after all but rather a coincidence that it started after messing with the relay. On Saturday morning I cleaned all the grounds on the LF fender and left side of the motor hoping it was a ground issue but this did not solve the problem.

I have confirmed voltage for ECM EG-328 Step 1 and EG-329 Step 2, confirmed fuse continuity EG-329 Step 4, confirmed voltage EG-330 Step 6, confirmed fuse continuity EG-331 Step 7, confirmed relay(s) behave correctly EG-330 Step 8 (see above).

I have confirmed fuel returning to the tank by removing the return line from the pressure regulator.

I thought it may be the fuel relay located in the front fender because the engine died both times while acclerating from idle and beleived it may not be switching from low pressure to high pressure. I removed the relay from the front fender and tested it per the FSM and it passed the test.

Can the fusible links have continuity from end to end yet still be bad?

Can the ignition switch EG-330 Step 5 be faulty yet still crank but not even fire or run?

I'm a bit baffled at the moment so more insight and thoughts from the forum is much appreciated.

 

[Malleus]

The fusible link is just a wire. If it has continuity, it's good.

The ignition switch could be faulty; it just sends power to the starter when it's turned to that position (one side is isolated then) and returns to complete a power circuit when you release it (have a look at the power source circuit diagram).

The AM1 side switches from ACC to IG1 (that's the released but on position) to the ST1 position (to power the starter), while AM2 is the IG2 side of the switch. So, you could conceivably have power to the starter but only half of the ignition circuit powered, if your ignition switch is bad.

IG1 powers the ECU-IG circuit, which the fuel pump needs. This "could" be a problem, but...

From your observations, it sounds more likely that you have a bad connection at the bottom of the engine compartment fuse block. I'd start there; much easier to confirm or deny that problem.

 

[artech]

Somebody here before was having a similar problem and it turned out to be a faulty immobilizer circuit in the alarm system. You might try searching for that here, the box is going to be either under the driver's seat or in the driver's kick panel. His problem was due to corrosion in the alarm box IIRC.

 

[alwaysmonday]

Somebody here before was having a similar problem and it turned out to be a faulty immobilizer circuit in the alarm system. You might try searching for that here, the box is going to be either under the driver's seat or in the driver's kick panel. His problem was due to corrosion in the alarm box IIRC.

Can the alarm box be removed completely without any repercussions?

 

[artech]

I yanked mine years ago and it hasn't caused any issues, but apparently there are several different types? I don't even remember what type mine was. I don't miss it.

 

[Rusty Marlin]

Can the fusible links have continuity from end to end yet still be bad?

Yes, I had this. I finally found it was truley bad by manipilating the FL while checking continuity. It would show/not show continutity while wiggling the link.

I didn't try and translate,

"I have confirmed voltage for ECM EG-328 Step 1 and EG-329 Step 2, confirmed fuse continuity EG-329 Step 4, confirmed voltage EG-330 Step 6, confirmed fuse continuity EG-331 Step 7, confirmed relay(s) behave correctly EG-330 Step 8 (see above)."

Have you confirmed the fuel injectors are firing? Not that they have voltage, but are actually cycling.

The truck started on Friday night after messing around with the EFI relay in the fuse box on the LF inner fender.

This makes me think you have a corrosion issue in or under the fuse box.

 

[alwaysmonday]

GOT IT RUNNING! I believe it was a poor ground on the bracket that the ignitor is mounted on. I didn't know that the bracket was bolted to the shock tower. It appeared from the engine bay that the bracket was welded to the shock mount. I was looking through the inner fender well and saw a bolt that had a wire grounded to it (I had previously cleaned all the griunds on the inner fender and the intake manifold but couldn'tsee this one from up above). I took off the bolt and sanded the shock tower, the bracket and the bolt. Put it back on and had my daughter crank it over and it started and ran rough on 4 cylinders (plug 1 was full removed from the head and plug 2 was in the head but the plug wire was disconnected). She shut it down and we put plug 1 in and hooked up the plug wires on plug 1 and 2. The it started right up. I drove it around the block and turned in on and off several times and it works perfectly. I think that it starts quicker, runs smoother and seems to have a bit more power. All this would make since because it had weak spark before due to the poor ground.

This bracket mounting bolt and ground placed next to the front tire makes it susceptible to corrosion due to all the dirt, grime and water splashed on it by the tire.

Thanks for everyones help trying to guide me through this and diagnose it. The Forum and the resources here are fantastic!