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Have a question from the Renix Gurus

old_man

old_man

NAXJA Forum User
Location
Loveland, Colorado
Well even us old timers that have been at the a long time sometimes need to confirm something. I have lost my injector pulses. It fires if I spray ether in the intake.

It has always been my position that if the camshaft position sensor in the distributor goes out, you would still get injector pulses. Can anybody absolutely confirm that for me?

I have a SnapOn 2500 scanner and for some reason it can't seem to talk to the ECU. I know an ECU failure is rare, but that is what it is looking like.

The story behind the story......I took it to get emission, it was running great when I drove it in and when I drove it out, it ran like crap. I pulled the plugs and they were covered with a fresh coating of soot. I pulled the O2 sensor to swap it out with my spare, but I found out my spare was for my old 2.5L, so I put it back in. It ran find for a short distance then started running like crap. When I pulled into my driveway and shut it off, it wouldn't start again.
 
jap813 said:
sounds to me like they fried your ecu for you
Click to expand...

They don't tie into the computer on the test. It is a simple dyno run with a tail pipe sniffer.
 
If the sensor in the distributor fails, your injectors will "batch fire" rather than fire sequentially with the firing order. Probably wouldn't notice it.

MAP sensor vac line or harness failure will cause extremely rich conditions.
 
I'm getting zero injector firing.
 
That is bizzare. If I spray carb cleaner or ether in the intake, it will fire and run for a second. I simply am getting no fuel out the injectors. The fuel pressure is fine. The injectors are fired from the drivers in the ECU, so if the injectors are not firing, it has to do with either the wiring or ECU or a signal feeding the ECU. The odds of all the injector wires failing at the same time is remote.

My question is....what can cause no injector pulses but not keep the spark plugs from firing? The cam position sensor syncronizes the injectors and ultimately sets whether the spark occurs on the right cycle. In other words, my question is....will a bad cam position sensor shut down the injectors but not the spark?

I will backprobe the sensor tomorrow and maybe try to swap in my spare ECU even though it is for a manual tranny.
 
Blown injector drivers will keep the injectors from firing, but will still allow spark. RENIX runs just fine without the CMP (I've checked this myself by experimentation,) and it will even start without the CMP, it just needs to "guess" until it hits the right firing order.

Find a thread by Mr_W on replacing injector drivers - I know he put it up here, and came up with a repair using COTS parts. Methinks that's what's happened to you. It's the only real "failure" of the RENIX ECU I've heard of...
 
5-90 said:
Blown injector drivers will keep the injectors from firing, but will still allow spark. RENIX runs just fine without the CMP (I've checked this myself by experimentation,) and it will even start without the CMP, it just needs to "guess" until it hits the right firing order.

Find a thread by Mr_W on replacing injector drivers - I know he put it up here, and came up with a repair using COTS parts. Methinks that's what's happened to you. It's the only real "failure" of the RENIX ECU I've heard of...
Click to expand...
I'm an electrical engineer. Odds of having all the injector drivers go bad at once is pretty much nill. Sounds like the ECU may have gone south.
 
Note from DJ
If they do the fuel system pressure checks in Colorado which they do hear in California now. Make sure the tester didn’t leave there clamping device on the fuel return line at the back of the fuel rail. Which I think might cause an extremely rich running condition caused by the very high fuel pressure that the ECU could not compensate fore.
But you’re spray carb cleaner or ether in the intake may have diluted the mixture enough to have allowed momentary combustion.
 
Note from DJ
Hear is some more info I saved
What is the voltage to fuel injectors?
http://www.naxja.org/forum/showthread.php?t=40941
OP by BSD: 12-2-2004
I just replaced my fuel injectors. One of the cylinders was not running. All was fine before. I am getting spark but doubt I am getting fuel to it. I have voltage on the plug that goes to the injector. However, I do not know if it is the right amount. It also seems to vary when I checked at another plug.
------------------
Post # 2 By 5-90:
What reading did you get?

I believe it's +12VDC, but A) I'd have to check and B) it's a pulsed voltage, so you'll have trouble getting a good reading with a voltmeter - you're better off trying to read injector pulses with an O-scope.

If you get a steady voltage (a quick check can be done with an analog voltmeter - watch for needle "tics",) then there is a problem somewhere that merits investigation. No voltage - no signal from the driver, and find out where it's getting lost.

Since the injector signal is supposed to run a duty cycle of 30-80%, you really should use a 'scope to read it
---------------------
Post # 6 by Matthew Currie:
You don't say what year, but if it's a 91-up, the ECU switches the negative side of the injector. Each injector should have +12 volts at all times when the ignition is on, relative to ground. If the voltage is not +12 at each injector, there is a fault in the harness or the positive supply, which comes from the ignition (exactly where I forget, could look up, but it's fed as I recall from one of the coil supply wires).

If it's a pre-91, and if I'm reading the fuzzy little schematic I have correctly, the ECU switches the positive side, but presumably the impulse should be pretty close to +12 volts at each injector. I say "presumably" because past experience with a bad wiring harness on a 93 suggests that the injectors won't fire reliably if the voltage drops more than a couple of volts. If the impulses are very short, it might be pretty difficult to measure because many meters will not respond quickly enough. If there really is a question on the voltage you might need to find someone with an oscilloscope to get a definitive answer, as 5-90 suggests.
------------------------------
Post # 7 by gptherezonlyone:
If it's a pre-91: The ASD relay supplies 12+ to the coil, O2 sensor heaters and the positive side of the coil within the injector. The PCM sends a ground signal to the heaters to turn them on and through the monitoring of the crank and cam (distributor) pickup it will pulse a ground to the coil and to each injector through the other wire. You can tell the difference on the wire. All the injectors will have one wire the same color, this one is the 12v+ from the ASD relay. The other wire is the ground from the PCM. It is only grounded when the PCM want the injector on. With the engine running voltage changes but the PCM monitors this and adjusts injector pulse width accordingly. One wire on each injector should be equal to battery voltage and the other will be 12v+ until the PCM grounds it and it fires (very short interval). Use a node light not a test light. A digital multi-meter might not be fast enough to sense it.
-------------------------
Post # 8 by Matthew Currie:
I must add here, however, that the dedicated injector and harness tester I used did not catch a low voltage at a connector caused by resistance in the harness. There was voltage enough to light the tester, but not enough to fire the injector once it heated up. So if a harness problem is suspected, I'd check the wires themselves with an ohmmeter.
 
Note from DJ
This is another possible solution;
Anti flooding feature controlled by the TPS
There is an anti flooding feature that is controlled by the TPS. Depress the foot feed to its maximum and try starting, when you do this it interrupts the signal to the injectors as long as throttle is completely depressed.
 
The injectors share a common ground that goes through number of splices. Maybe check the ground at the number one injector to battery negative.
The TPS full short will shut down the injectors.
I'm not exactly sure what an open crank signal to the ECU will do during starting (I never tried it). The book says it is one of the necessary inputs during start mode.
 
Posted # 19 by Curtis_H: http://www.naxja.org/forum/showthread.php?t=1053601&page=2
I had this in the Waggy for a long time. I changed every damn sensor on the engine literally. Also put in new ford injectors. When that didn’t work I started looking at the wiring. Check the input voltage on the map sensor and the TPS, both should be at or very near 5v. Check the resistance to the negative post on the battery from both sensor grounds. There should be very little to none. I ended up cleaning all my grounds, adding a 4/0 ground from battery to body, cleaning every connector on every sensor, replacing a few bad ones, fixing a couple of corroded wires here and there and now it is running much better. I still can't say it is perfect, but it is much better. Renix are extremely finicky when it comes to grounds so check every one you can find and then find the ones you cant see and check those and then add a couple and check those too and then re check them all and add 37 more and you should be good to go!!
Or Joe Peters quote “You have got to have good grounds. Without good grounds your coffee will taste like crap and your electrical components will behave erratically”.
 
Is this what you are referring to 8Mud
From the post The RenX Files: High idle problems
Sensor circuit shared ground splice P7
Post # 93 by 8Mud
http://www.naxja.org/forum/showthread.php?t=905849&highlight=renix+files&page=7
The major problem was the sensor circuit shared ground splice under the harness plastic sheath, maybe 8 inches on the sensor side of the C101 Connector. Three sensor wires, TPS, Engine temp. to the ECU ground and another I haven't identified. Go to one ground wire through the C101 and then to the ECU. Long story short, somebody did a poor job of crimping the squeeze connector. I had between 4.5 and 61 ohms of resistance depending on how I twisted the harness.
 
djgrayxj said:
Is this what you are referring to 8Mud
From the post The RenX Files: High idle problems
Sensor circuit shared ground splice P7
Post # 93 by 8Mud
http://www.naxja.org/forum/showthread.php?t=905849&highlight=renix+files&page=7
The major problem was the sensor circuit shared ground splice under the harness plastic sheath, maybe 8 inches on the sensor side of the C101 Connector. Three sensor wires, TPS, Engine temp. to the ECU ground and another I haven't identified. Go to one ground wire through the C101 and then to the ECU. Long story short, somebody did a poor job of crimping the squeeze connector. I had between 4.5 and 61 ohms of resistance depending on how I twisted the harness.
Click to expand...

Each of the injectors spices into a common ground, some double spliced and some single, in effect it is largely in series. I'm not exactly sure how or where it all joins up, I just know it all ends as a common ground at the dipstick holder (I've never striped back the entire harness and exposed all the wires and splices). The wires in the injector harness are prone to fatigue under the insulation near the bend at the firewall. One of the first of many electric problems I found in my 87 around twenty years ago was a fatigued injector wire under the insulation, which could just as easily have been a fatigued ground wire. I've found numerous splice problems in different places, some harder to pin down that others.

Worth looking at before ECU replacement, may or may not be *the* problem but a trouble spot worth looking at.
 
djgrayxj said:
Is this what you are referring to 8Mud
From the post The RenX Files: High idle problems
Sensor circuit shared ground splice P7
Post # 93 by 8Mud
http://www.naxja.org/forum/showthread.php?t=905849&highlight=renix+files&page=7
The major problem was the sensor circuit shared ground splice under the harness plastic sheath, maybe 8 inches on the sensor side of the C101 Connector. Three sensor wires, TPS, Engine temp. to the ECU ground and another I haven't identified. Go to one ground wire through the C101 and then to the ECU. Long story short, somebody did a poor job of crimping the squeeze connector. I had between 4.5 and 61 ohms of resistance depending on how I twisted the harness.
Click to expand...

Just did this repair on my wife's XJ. Three sensor grounds are connected to one wire about 8 inches on the engine side of the harness. They are for TPS, CTS, and IAT. All brown with white wires BTW. Then, the single wire goes into and exits from the C101. About a foot down the chassis side of the harness the single wire is spliced again to three wires. One goes to ECU ground, one to MAP, and one to the diagnostic connecter on the passenger side fenderwell. The splice/crimps were very poor. By wiggling either side of the harness, I could vary the resistance from 38 to 74 ohms. The solution is to locate both of the splices and solder both sets of three wires together bypassing the C101. Very easy.

The C101 is always highly suspect as are the grounds on the block.
I have the pin-out of the diagnostic connectors if you need them.
 
cruiser54 said:
Just did this repair on my wife's XJ. Three sensor grounds are connected to one wire about 8 inches on the engine side of the harness. They are for TPS, CTS, and IAT. All brown with white wires BTW. Then, the single wire goes into and exits from the C101. About a foot down the chassis side of the harness the single wire is spliced again to three wires. One goes to ECU ground, one to MAP, and one to the diagnostic connecter on the passenger side fenderwell. The splice/crimps were very poor. By wiggling either side of the harness, I could vary the resistance from 38 to 74 ohms. The solution is to locate both of the splices and solder both sets of three wires together bypassing the C101. Very easy.

The C101 is always highly suspect as are the grounds on the block.
I have the pin-out of the diagnostic connectors if you need them.
Click to expand...
When I went from the 2.5L over to the stroker, I removed the C101 connector.
 
djgrayxj said:
Note from DJ
This is another possible solution;
Anti flooding feature controlled by the TPS
There is an anti flooding feature that is controlled by the TPS. Depress the foot feed to its maximum and try starting, when you do this it interrupts the signal to the injectors as long as throttle is completely depressed.
Click to expand...

Thanks. I didn't think of that. I will check it. It could cause the problem as well.
 
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