Renix Questions. Semi starts, dies after 1-3 seconds....

HELP! lol need some Renix advice! So I went and looked at an 89 Renix today, scratching my head over it pretty bad. At first is had no spark, replaced the ignition control module and coil. Now has spark, at the coil, at the plugs, then it back fired, found the distributor out of time. Reset timing on the distributor. now everything is in time. has good spark, removed the rail and watched the spray patterns and fuel come out of the injectors, has fuel coming out all 6 injectors. CPS is new, Checked the Cam sensor (its working), replaced the map sensor, has a new fuel pump, has good plugs, wires, cap, rotor. all grounds are good, fuses are good. Fuel pump ballast resistor is bypassed and pump is on toggle (is pumping). Crimped off fuel return line to boost pressure and eliminate fuel pressure regulator. No change still wont run. Fuel was put in about 1-2 months ago, smells normal. Checked for power/ground at injectors (even thought hey do spray in timed pattern when rail is backed off an inch or two) injectors have power/ground and do pulse when cranking.
have tried a different renix ecm. Still wont start....

It will Crank and start for 1-3 seconds then sputter out. If I spray carb cleaner in the intake it will continue to run as long as I spray it, then it dies.

Any ideas? I am leaning towards it dropping the injector signal 1-3 seconds after start, or ecm. and the ecm didn't make a difference because timing was off (180* out) hard to tell.

I am car savy, but not Renix inclined LOL any ideas?

You have diagnosed it to being a loss of fuel. Sounds like a fuel pump relay or ballast resistor.

old_man said:

You have diagnosed it to being a loss of fuel. Sounds like a fuel pump relay or ballast resistor.

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both are bypassed, the pump is hard wired to the battery with key on and a toggle for "off" which is why I am getting confused. I feel like I am walking in circles and staring at the obvious lol

Do a fuel pressure test, should be 31psi with vacuum hose connected and 39psi with no vacuum at the regulator.

What exactly does "hard wired to the battery with key on" mean?

Have you put a fuel pressure gauge on it and watch to verify fuel pressure?

Have you tested the CPS to verify it is giving a steady >0.50 AC volts while cranking?
Renix is notorious for a weak CPS signal, there is a fix where we mount it closer to the flex plate, and boost the signal, explained in old threads here. Also many have report defective CPSs right out of the box lately, me included. Mine worked sometimes, then finally went open circuit when I was looking and then back to working, LOL!!! Took me weeks to catch it in the act!!!! It had a loose internal wiring contact.

At first guess, check your MAP sensor vacuum line and make sure it is plugged into the right hole. One is a blind hole, the other vacuum. When the key hits run you get a baseline vacuum reading from the MAP before the motor is started. When/if it starts the MAP may be telling the computer you are getting no vacuum, which tends to scramble the brains.

Set the distributor back to stock, find TDC "1", drop the distributor back in there so the rotor is near the "1" pole on the cap- The cap often has a one mark on it. If it isn't marked for one, find a picture showing where one should be. In my experience any timing done to the distributor either doesn't help a lick and can actually cause grief. The ECU compensates for timing over a pretty broad range, it will often run with the distributor indexed one full cylinder off, fine adjustments are basically most often a waste of time.

Do a fuel pressure check and/or a flow test. I'd put everything back to as near a stock configuration as possible. You may be building more problems in than you are solving.

Now back to the MAP being plugged into the wrong hole, it may cause spark and timing issues. The usual results are clouds of smoke (unburned fuel) out the exhaust. The motor may run (barely), but refuses to build RPM's.

CPS, the CPS itself is only part of the problem, the CPS wires can get fried on the exhaust, the wiring and/or connectors between the CPS and the ECU may have resistance in them. The signal form the CPS to the ECU is tiny, any problems in the harness are going to cause grief-

my2monkeys said:

Do a fuel pressure test, should be 31psi with vacuum hose connected and 39psi with no vacuum at the regulator.

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Will do it again, I didn't personally do it as I didn't bring a gauge with me, but when it died on him he checked it, said it was bad/no pressure. replaced the pump and it was good (few weeks ago) I told him to recheck it.

Ecomike said:

What exactly does "hard wired to the battery with key on" mean?

Have you put a fuel pressure gauge on it and watch to verify fuel pressure?

Have you tested the CPS to verify it is giving a steady >0.50 AC volts while cranking?
Renix is notorious for a weak CPS signal, there is a fix where we mount it closer to the flex plate, and boost the signal, explained in old threads here. Also many have report defective CPSs right out of the box lately, me included. Mine worked sometimes, then finally went open circuit when I was looking and then back to working, LOL!!! Took me weeks to catch it in the act!!!! It had a loose internal wiring contact.

Click to expand...

The factory fuel pump wiring has been bypassed, the power/ground is ran to the battery with a switch on the ground side IIRC and wired to a ignition source to only run when the key is in "run" "start" or "Acc" Positions. I can't remember the explanation but it was done a year or so ago and was working fine.

The pump turns on and is pumping, as far as pressure not 100% on as I didn't have the gauge to see it myself. was told it was good, but told the owner to recheck it (its an hr drive from me, or I would my self)

I have not verified the CPS signal. interesting on a bunch of bad new ones... I'll check that after he checks fuel pressure and pulse signal with noide lights.

QUOTE=8Mud;245756747]At first guess, check your MAP sensor vacuum line and make sure it is plugged into the right hole. One is a blind hole, the other vacuum. When the key hits run you get a baseline vacuum reading from the MAP before the motor is started. When/if it starts the MAP may be telling the computer you are getting no vacuum, which tends to scramble the brains.

Set the distributor back to stock, find TDC "1", drop the distributor back in there so the rotor is near the "1" pole on the cap- The cap often has a one mark on it. If it isn't marked for one, find a picture showing where one should be. In my experience any timing done to the distributor either doesn't help a lick and can actually cause grief. The ECU compensates for timing over a pretty broad range, it will often run with the distributor indexed one full cylinder off, fine adjustments are basically most often a waste of time.

Do a fuel pressure check and/or a flow test. I'd put everything back to as near a stock configuration as possible. You may be building more problems in than you are solving.

Now back to the MAP being plugged into the wrong hole, it may cause spark and timing issues. The usual results are clouds of smoke (unburned fuel) out the exhaust. The motor may run (barely), but refuses to build RPM's.

CPS, the CPS itself is only part of the problem, the CPS wires can get fried on the exhaust, the wiring and/or connectors between the CPS and the ECU may have resistance in them. The signal form the CPS to the ECU is tiny, any problems in the harness are going to cause grief-[/QUOTE]

the vacuum line is in the correct hole from what I am told (lower one of the two) I though it was odd how there was 2 and only one being used, but I guess one is a plugged port? I'll look it up to verify its the right one.

I did reset the distributor to stock, its at cyl 1 on the cap while at TDC (compression stroke) all the wires are ran correctly as well.

the fuel pressure test and flow test is what I am wanting to do next, hopefully today or tomorrow. as well as pulse test. I wanted to put things back to stock but that part of the harness is not reusable at the moment. may have to though.

No smoke or noise when it does run other then it dies LOL does not miss-fire when I spray carb cleaner in the intake. or stumble, it runs really well.

I ran my hand across the CPS harness and looked at it for any cuts/noticeable problems. I didn't see any, but will ohm them out next time I can make it down there.


Thanks for all the ideas and help guys. I will report back once things have been checked further or fixed!

Do the volume test, volume and pressure are two different things. Pull the fuel filter and tap it gently with the input side down on a piece of wood and see what comes out. Even if it is fairly new, it can still be partially plugged with rust flakes or what not.

I'm with Mike, how did you wire it direct and have it work with the ignition switch? If you don't have a relay and it turns on with the ignition switch, you may be getting low amps. Low amps will often show up as low voltage at the pump, especially with the pump running. When it does start for the few seconds, check the voltage at the pump and see what happens. Best to skin back a little the wire and do it with the pump connected.

The volume test will also tell you if the pickup tube has come off or is rotten through. If you get low volume check the simple stuff first, like loosening the gas cap. Not a bad idea to disconnect fuel line at the rail while you have the filter off and blow some air through there, use a catch pan so you can see what comes out.

Make sure you are clamping the output line off, if you clamp anything off. The regulator is on the return line if I remember correctly, I may be wrong, it has been awhile, ask Mike to check for certain. Getting old sucks, I've likely forgotten more than I actually remember .

8Mud said:

Do the volume test, volume and pressure are two different things. Pull the fuel filter and tap it gently with the input side down on a piece of wood and see what comes out. Even if it is fairly new, it can still be partially plugged with rust flakes or what not.

I'm with Mike, how did you wire it direct and have it work with the ignition switch? If you don't have a relay and it turns on with the ignition switch, you may be getting low amps. Low amps will often show up as low voltage at the pump, especially with the pump running. When it does start for the few seconds, check the voltage at the pump and see what happens. Best to skin back a little the wire and do it with the pump connected.

The volume test will also tell you if the pickup tube has come off or is rotten through. If you get low volume check the simple stuff first, like loosening the gas cap. Not a bad idea to disconnect fuel line at the rail while you have the filter off and blow some air through there, use a catch pan so you can see what comes out.

Make sure you are clamping the output line off, if you clamp anything off. The regulator is on the return line if I remember correctly, I may be wrong, it has been awhile, ask Mike to check for certain. Getting old sucks, I've likely forgotten more than I actually remember .

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Will do. I was clamping the return (off the regulator on teh fuel rail) the line would get solid and could hear the pump start to stall out from pressure.

as far as the pump wiring I am not 100% sure on how its wires, I jsut now there is a wire I can take of the abttery to kill the pump thats NOT factory, I asked about it and was told "its wired hot to the battery and turns off with the key... maybe theyre is a seperate switch... I'll ask further details on it.

Ecomike said:

You said it would run if you sprayed fuel into the throttle body. Are you opening the throttle to spray it in? If yes, you are also opening up the air feed!!!!! In which case your problem may be a stuck IAC valve starving the engine for idle air at start up!!!​

If I am right, floor the gas peddle, crank and see if it will start and run at say 2000 rpm!!!! (do not let completely off the gas!!!!)​

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yes it will run with carb cleaner jsut fine, throttle closed it idles normaly. did not open the throttle. if I try to start it with the throttle open it wont. which makes me think its back to pressure/volume.

Thanks agian!

Unless you missed something, or something changed, it sounds like a lack of fuel!!!

Grab a noid light and watch the injector pulses and see if they go away.

removed the rail and watched the spray patterns and fuel come out of the injectors, has fuel coming out all 6 injectors

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How were you able to do this?

Sorta weird that it has fuel and spark and it still doesn't run.

double post

Ecomike said:

Unless you missed something, or something changed, it sounds like a lack of fuel!!!

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I agree!

old_man said:

Grab a noid light and watch the injector pulses and see if they go away.

Click to expand...

thats what I am trying to get him to do at the momment.

my2monkeys said:

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How were you able to do this?

Sorta weird that it has fuel and spark and it still doesn't run.

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I took out the 4 bolts. backed the rail out of the intake about 2-3 inches and watched them pulsate 1 by 1 and saw all 6 spray in a uniform pattern. then bolted it back up.

I agree.

Ok, Fuel pressure is still reading good at 40psi with key on, cranking and running drops to 37-38 ish psi. (Good)

With noid lights the lights light up for 1-2 seconds then stop, and it dies. lossing power (ground is good to all injectors) Does this mean its the ECM? or could a sensor be causing it to stop? My personal thoughts are thats its the ECM. case closed... or am I over looking somthing that is a special Renix thing LOL

Running, the fuel pressure should drop to 31 psi (Vacuum hose attached). It could be flooding???? Are you sure the Pressure reg is not leaking fuel into the vacuum line? I realize other data says this is not likely, but when confronting conflicting data, it is time start over on checking some things.

Have you checked to see if the ignition switch is going bad, the linkage is off on the switch, or the wiring at the switch is fried? ECU needs many good inputs, any of which could be causing it to shut down.

Something may be loose in the wiring harness, that loosens when the engine runs (moves, shakes....) and kills the operation. Did you test the CPS for .50 cranking Volts AC yet (Isolated from the harness)?

Have you gone through Crusiser54's ground refresh procedure? Their are about four hidden ECU sensor control items ground splices in the harness that have crimps that get loose with age!!!

Renix ECUs almost never go bad. But there have been a few reported ones (3 or 4 in the last 6 years here) that had bad parts on one of the injector firing circuits on the board, that caused a rough idle.

The question is what happened first, did it die for lack of CPS signal, flood, get too lean, loose spark, ...... and then the ECU turned off the injectors, or ?????? The diagnostic trick is determine which happened first in a millisecond or two!!!

Ecomike said:

Running, the fuel pressure should drop to 31 psi (Vacuum hose attached). It could be flooding???? Are you sure the Pressure reg is not leaking fuel into the vacuum line? I realize other data says this is not likely, but when confronting conflicting data, it is time start over on checking some things.

Have you checked to see if the ignition switch is going bad, the linkage is off on the switch, or the wiring at the switch is fried? ECU needs many good inputs, any of which could be causing it to shut down.

Something may be loose in the wiring harness, that loosens when the engine runs (moves, shakes....) and kills the operation. Did you test the CPS for .50 cranking Volts AC yet (Isolated from the harness)?

Have you gone through Crusiser54's ground refresh procedure? Their are about four hidden ECU sensor control items ground splices in the harness that have crimps that get loose with age!!!

Renix ECUs almost never go bad. But there have been a few reported ones (3 or 4 in the last 6 years here) that had bad parts on one of the injector firing circuits on the board, that caused a rough idle.

The question is what happened first, did it die for lack of CPS signal, flood, get too lean, loose spark, ...... and then the ECU turned off the injectors, or ?????? The diagnostic trick is determine which happened first in a millisecond or two!!!

Click to expand...

its not leaking intot he vacume port on the regulator as we ran it witht he hose off and nothing came out of the vacume side.

the ignition switch? woiuldn't it not crank? or not have power if the switch was bad/no connected?

I have not been able to make it down with my ohm meter to recheck the CPS. wouldn't a bad CPS cause a crank no start?

yes all grounds have been checked and cleaned (wire brush) as told to do so by cruiser54.

I am not sure as to what happens first, I jsut know that the noide light stops flashing and then it starts to die.

IIRC, you said it will run with carb cleaner feed into the throttle body.

So I doubt the ECU is deliberately turning off the fuel injector signal, as it would also deliberately turn off the spark, unless the ECU thinks the engine is way too rich? (That is where the high fuel pressure bothers me once it is running)

Are their any issues with the O2 sensor or wiring? Try disconnecting the O2 sensor and see if anything changes to be sure. RE-Check the FPR and vacuum line to it.

Ignition switch can get old, loose contacts, get flaky, corroded with age, and new ones may not be installed in the sweet spot, linkage wise, and can cause odd start, stop, run behavior.

But this one sounds like it is time to the pull the ECU, either swap in a known good one, or open the old one up and look at the firing circuits for burned hot spots, and search the old threads here for some info. One guy in Romania fixed his with a new diode and posted details her. Others just swapped out the ECU.

I would try disconnecting the O2 sensor first, and checking the wiring on it first, check for a wiring short that may be telling the ECU it is too rich! Then if that is OK go after the ECU.