No spark after engine swap...

[Jared]

So, do I need to remove the ECU, and check for continuity between a known good ground and the two ground connectors to the ECU? Is a bad ground to the ECU our prime suspect now?

 

[langer1]

The relay does not shut it down. The pump has its own pressure switch. If it keeps running, it is either the pump, the hose from the pump to the mounting bracket in the tank, or the pressure regulator. A If the pump keeps running and there is pressure, the pump has a problem, but that should not keep it from starting.

Not true, The ECU runs the pump for 3 seconds when the switch is turned to the run position, pressure or no pressure.

 

[langer1]

So does the ECU have a "starting mode" and a "running mode"? If so, what tells it which to do?

In the crank position the pump is turned back on, when running the signal from the CPS says the engine is running.

 

[langer1]

So, do I need to remove the ECU, and check for continuity between a known good ground and the two ground connectors to the ECU? Is a bad ground to the ECU our prime suspect now?

Or a bad ECU, but if it was ok before the swap it should be OK now. Some of the ECU ground wires are on the Dipstick bolt.
Heres what we know.
1. The ECU it not sending a spark signal.
2. The UCU in not sending a injector signal.
3. The ECU in not turning the fuel pump off after 3 seconds.
Did you mash some relays dropping the engine back in?

 

[old_man]

OK smart one, how does the computer know when to turn the pump on and off? Where is the pressure sensor the computer uses to sense the pressure? The pump has an internal pressure switch and shuts itself off after a few seconds when you apply the voltage, because the pump pressurized the lines. Go measure the voltage on the pump, it is always there when the key is on.

The only thing the relay does is after the engine is running and stops, it disco's the pump until the engine is started again. This is for safety reasons in a crash. If the pressure regulator is stuck open the pump will just continue to run when you turn on the switch.

 

[badge714]

Just a thought try spraying throttlebody cleaner into throttle body if it starts you have a fuel problem but at least you know where to start badge714

 

[langer1]

OK smart one, how does the computer know when to turn the pump on and off? Where is the pressure sensor the computer uses to sense the pressure? The pump has an internal pressure switch and shuts itself off after a few seconds when you apply the voltage, because the pump pressurized the lines. Go measure the voltage on the pump, it is always there when the key is on.

The only thing the relay does is after the engine is running and stops, it disco's the pump until the engine is started again. This is for safety reasons in a crash. If the pressure regulator is stuck open the pump will just continue to run when you turn on the switch.

Just because you’re a moderator is no reason to start name calling, but that’s ok.

 

[8Mud]

I haven´t got the wiring diagrams memorized, but the fuel pump relay and the O2 heater relay are dual function. If the fuel relay is stuck closed, it could affect the ECU during start.
Ignition on, then start, then run are the normal sequence, during start the fuel pump relay is in the open position (or just the opposite of the run position). Fuel pump seems to be on a timer at ignition on, full voltage at start and resisted voltage (low voltage) at run.
48 PSI seems way to high.
You got a half dozen guys, running you around in circles. But if you get bored, jump the solenoid wire straight to the battery without turning the key to start (but in the run position) and check for spark. If spark or not, this can help with the troubleshoot. Try it again, with the coil wire disconnected from the cap and the throttle held all the way open.
CPS 200 ohms +/- 75. Been awhile but Pinned the CPS wires once and put my analogue meter on the lowest AC volt, the needle jumped, tried it again on DC voltage and still got some motion. Did the same on cam position sensor the blue wire and the grey wire, needle jumped while cranking (wires pinned, connector connected).
I've had mixed results checking the CPS for pulse, think it has much to do with how good your meter is and which position it wants to read the pulse (it is a wave form), mine reads best at low voltage AC. The cam position sensor pulse was easier to read.
You can cut to the chase checking grounds, by pinning (straight pin through the wire,connector connected) the TPS ground wire, key in run and checking for voltage between the ground wire and the battery ground. It should read less than a volt, hopefully less. This lets you know if the ground circuit is interrupted or poor, all the way from the TPS to the motor ground for the ECU. Make the same test at the MAP ground. If it reads close to 5 volts the ground isn't there. Check the MAP input voltage.
Most of the failures I've seen in the ECU, where the power supplies. Instead of a 5 volt index to the sensors, there was no voltage or 12 volts. Usually happens when somebody hooks up the battery backwords, or during a jump start. If your getting a 5 volt (or there abouts) index voltage to the sensors, chances are the ECU is OK. If there is no index voltage, the problem may be the fusible link or the wire from the ignition switch to the ECU.
Hope I´ve helped more than confused.

 

[Jared]

Did you mash some relays dropping the engine back in?

I doubt it, most relays are on or near the fenders. A mashed or stretched wire is a possibility, but I've triple checked everywhere I can think of for signs of that.

So, if the ECU is getting power at both it's power supply wires, and both grounds are good we should assume that the ECU is bad?

A disconnected ground wire is looking to be the most promising route, given the nature of removing/installing an engine. I'll get fondling the transmission from below and look for any loose wires that I'd somehow missed.

Jared

 

[langer1]

I doubt it, most relays are on or near the fenders. A mashed or stretched wire is a possibility, but I've triple checked everywhere I can think of for signs of that.

So, if the ECU is getting power at both it's power supply wires, and both grounds are good we should assume that the ECU is bad?

A disconnected ground wire is looking to be the most promising route, given the nature of removing/installing an engine. I'll get fondling the transmission from below and look for any loose wires that I'd somehow missed.

Jared

I think so, the fuel pump running all the time is a clue to follow, the ECU should turn it off, I'm sure. Oldman read page 49(50) of the renix manual.

 

[8Mud]

I´d be more liable to think the fuel pump relay is stuck closed, I´ll have a look at the wiring diagram and see if anything jumps out at me. The fuel pump relay is grounded through the ECU and always under power. It doesn´t need a signal from the ECU to close, all it needs is a ground, either through the ECU or a short someplace.
Renix ECU´s are fairly bullet proof, I´d first think it was the imputs or the wiring.

 

[langer1]

Is this no correct Oldman?

 

[badge714]

Does your battery ground terminal have a small wire that comes off and goes to the fender as a ground wire There's a ground connector below intake manifold for injectors BADGE714

 

[8Mud]

One thing about Old Men, they have probably forgotten more than most youngsters know. The old hard drive gets full to overflowing.

 

[langer1]

One thing about Old Men, they have probably forgotten more than most youngsters know. The old hard drive gets full to overflowing.

One thing for sure he's knows what he's talking 99.9% of the time. I wish I knew half as much about jeeps.

 

[badge714]

8MUD got a question what is the SYNC sensor it's on the same power line as crankshaft sensor and oxygen sensor also MAP sensor. trying to figure out diagram for grandson XJ [email protected] badge714

 

[langer1]

8MUD got a question what is the SYNC sensor it's on the same power line as crankshaft sensor and oxygen sensor also MAP sensor. trying to figure out diagram for grandson XJ [email protected] badge714

Thats the pickup coil in the distributor, also called CKP or Cam position sensor.

 

[8Mud]

If I understand it correctly it´s supposed to tell the ECU when number 1 and number 6 are close to TDC exhaust. Or near the optimum point to inject and also indexes the whole fuel spark cycle. In conjunction with the CPS.
If it doesn't pick up a signal in so many revolutions, it´s supposed to default and start firing the injectors anyway.
I've forgotten and left mine unplugged, didn't seem to affect much of anything. But thinking about it a little, it may be a factor in long cranks, before starting.
Read somewhere the ECU will fire anyway if the sync sensor is faulty, but not optimally.
Think I´ll test mine and play with it a bit and see what happens.
I´m also gonna try starting mine with the MAP plug pulled, I've pulled it while it was running and it shut right down ( idle closed loop). MAP sends an atmospheric reference, to index the ECU at key on, no power no index. It may default or just may cause the ECU to say no to start or open loop operation.

 

[Jared]

I would think that the sync sensor would tell the ECU which TDC position a specific cylinder is at (TDC exhaust stroke vs TDC compression stroke). Since the crankshaft turns twice for each compression/exhaust cycle, the CPS alone would not supply enough data to the ECU to determine when to fire injectors and spark. It couldn't tell the difference between exhaust vs compression strokes. The sync sensor, however turns at only half the speed of the crank, and therefore would supply the ECU with the needed information to determine when to fire the injectors/spark. Hence the name, "sync" sensor.

Jared

 

[Jared]

Just a thought try spraying throttlebody cleaner into throttle body if it starts you have a fuel problem but at least you know where to start badge714

I've done the starting fluid test a few times. I actually got it to diesel a few sputters once. But there's still definately no spark.

Jared