LS1 ECU Issues

[dcrosby]

I'm having some strange issues, for one, the car was running, and has been for over 4 Years now, on the same tune, same ECU, same Everything.

I'm on the on ramp, and mid on-ramp the car falls flat on it's face .... I put it in gear, and no power, can't start it again, and I coast to the right of the freeway/interstate.

I get a tow, back home, and nothing I can see is wrong with the car. So I start checking fuses, all are ok, and not burnt out. So I look at the coil voltage, as by my gauges I can see I'm getting Fuel, Fuel Pressure reads 40-50 PSI. So I look at my plugs, and they seem fine, nice color, nothing wrong, maybe the gap is a bit bigger than when I put them in 4 Years ago, but fine. So I look at the Pink Wires going to the coils. 8v Drivers Side and 9-10v Passenger.

And I'm thinking, that's not right it's supposed to be 12v. 

The Battery Optima Red Top is Less than a Year old, and charges to 100% and roughly 13.4v.

So I check the fuses again, and I notice the fuse that goes to the switched 12V on the ECU when removed, has 12v, but when plugged in and has power it drops to 9-10v.... so I'm thinking "AHA!" And start tracing the wire, and find little to remark about, some stereo stuff that I had disconnected over a year ago, and now removed all together "Just in case", and I've been working a couple of hours a weekend on this bloody thing, and I now ordered a new ECU, just to see if it'll fire... Since it turns over just fine... just doesn't fire... most likely because of the 8V on the coils...

Oh and I also removed one of the plugs and grounded it, to see if I could see spark when I cranked it... no nothing.... and I do smell some fuel coming from that spark plug hole...
Speaking of grounding, the harness was grounded to the firewall, and secure, and I had good grounds from the fuse box...

Any Ideas, suggestions, or stories of "Oh Yeah that happened to me" are welcome, also this may be useful for someone in the future searching, and finding what I when through, and what was the ultimate solution, as I intend to update this...

And Here are some images since pictures make things seem saner than they are...

Ground Straps


Spark Plug Removed, and Grounded, as well as location of pink wires I am checking


Charger reading when battery was fully charged

[dcrosby]

Well the ECU Failed me, or didn't as the case may be, the replacement ECU did the same thing 8.5 v on the pink wire at the coils, on one side, and 9-10v on the other... Same Issues It Doesn't Fire...

I'm running out of ideas, other than re-wiring power to the ECU from scratch... :O

This Really Sucks, I don't understand what could have worn out / changed during driving... A Bad Rectifier or something would make sense... but this is NUTS.... I could change the battery, but unless everything is lying to me the Optima Red top with Less than 12 Mo. on it is fine...

Something could have melted together (Wires), but again, the car ran fine for nearly 4 Years... what could have suddenly changed ? With the old FD Harnesses it's a heat issue, and brittle wires, all the wires I have checked have very pliable insulation....

[dcrosby]

I have gone through all the advice I've gotten:
Check Pins 1 & 40 on both the Blue and Red Connector on the ECU, both (Plugs) have .01 ohms resistance and show continuity to the frame...

Check the Brown and Black Wires on the Coil Pack Plug (Pictured) and see if you get solid grounds...
Well neither side Brown Wire did show a continuity signal, the Passenger side black signal did, and I have the Picture of the Multimeter Of what it showed... (27 Ohms)


The Black Wire on the Drivers side did not show continuity but had a massive amount of resistance... (almost 1 Mega Ohm)


I'm gonna say that may not be normal....

[dcrosby]

This is how far I got on the RX-7 Club Forum, I used to be part of V8RX7Club.com or some such, so sorry for not posting here first, I didn't know what it had been renamed to, the car ran so well for 4 Years I had little need for the insane amount of support the original rotary builds needed... but the FD rears its ugly head once more with a flabbergasting problem...

Any and all help is of course very appreciated, and needed for further searches and others with similar issues. And Yes I searched extensively before posting this... I couldn't even find anything remotely similar on LS1Tech so it's safe to say this may be some strange manifestation...

Regardless I want to keep people apprised of my search for an answer in case this is not an isolated case and may befall a lot of Hinson Kit People... as they are the ones who modified my harness, but not to blame, as of yet, and I'm not looking for a witch hunt, just to find a solution and to inform others....

[RX7V8Builder]

The pink wires with +12 run directly from ignition to the coils.  they dont go thru the ECM.  Check for 12V to the battery negative as reference, not the shock mount.  Could be the ignition switch.
Where is your battery ground connected to?  should go to the engine block and chassis.
Those harness grounds would be better on the block, on the back of the dr. side head.
Do you have a ground strap between the engine block and the chassis too?
 

[digitalsolo]

That harness ground location sucks.   Did you clean the paint off behind it?

Explain your chassis grounds, locations, etc, as well as your engine grounds.

[dead2me]

That harness ground location sucks.   Did you clean the paint off behind it?

Explain your chassis grounds, locations, etc, as well as your engine grounds.

what he said.  I bought someone else's unfinished project which had a painless harness on an LT1.  Everything looked good, the harness was connected to all things necessary, and the bastard would not start.  It showed 12 volts to the PCM etc when the key was on.  It would turn over, but never fire.  I finally checked the 12v feed to the PCM  while cranking and it dropped substantially below 12v.  I connected it directly to battery, with a fuse of course, and it fired right up.  I added a good ground strap and had to find a better 12v feed when the key was on.  One thing I have noticed in a lot of similar threads is a ground issue.   When I remote-mounted my battery in the FD, I ran both positve and negative from the bin all the way to the engine bay, and then a ground strap connecting it to the engine from the same point you have yours connected, basically using body ground as a backup or common plenum, as I just don't trust body ground, preferring to always run a dedicated cable.  It always works better, and another guy on the forum was working on the car with me and said that mine doesn't struggle to turn the engine over the way his does, which uses the body for ground instead of a separate cable.  Cable is a lot cheaper than gray hair 

Just a thought or 2...   Sometimes it's the painfully simple things...  Here's to hoping yours is solved shortly. 

[dcrosby]

Well I wish the cable thing was the issue, as I spent another $50 to find out my grounds are solid...

4AWG Wire to the left of the negative multimeter probe, runs straight to negative terminal... I have a feeling something else on that 12V circuit has either malfunctioned, and has a short but not one with 0ohms, so it functions like a large resistor, but if that were the case it should smoke, and eventually burn and fail... but nothing have had the key on run for sometimes an hour and no smoke no fuses fail... very bizarre...

Oh and I have replaced the old plug I had in teh previous pictures with a brand new platinum plug, and nothing... no spark...

[Pez]

Why haven't you checked the coil wire power source?

[Jordan Innovations]

That harness ground location sucks.   Did you clean the paint off behind it?

Explain your chassis grounds, locations, etc, as well as your engine grounds.

Those engine grounds should be to the heads, not the firewall.  Then ensure that your engine to chassis ground is good.

I know it sounds a little harsh, but I'm almost certain you have a grounding problem, as evidenced by the fact that you think the coil bracket is a grounding location for your measurements.

[dcrosby]

Why haven't you checked the coil wire power source?

Sorry Can you elaborate ? Where... I thought the Pink Wire was the coil wire power source... it's switched 12V... and I can't get more than 9v out of it...

[dcrosby]

That harness ground location sucks.   Did you clean the paint off behind it?

Explain your chassis grounds, locations, etc, as well as your engine grounds.

Those engine grounds should be to the heads, not the firewall.  Then ensure that your engine to chassis ground is good.

I know it sounds a little harsh, but I'm almost certain you have a grounding problem, as evidenced by the fact that you think the coil bracket is a grounding location for your measurements.

Well I do appreciate the input harsh or not, but the fact that the car ran for 4 Years with those grounds, and they're tight, leads me to believe either A they're adequate, or B they were adequate before something else fell of / burned through / melted, so they no longer are.
So either I'm chasing something that changed, or I'm chasing my own tail, since the car died while running, with those grounds.

And it's not that I'm not following people's advice, but part of the cable I added was getting/making a ground kit, and attaching a loop from that location on the firewall (current grounds), to the cylinder head, my first try was to go from the battery to the cylinder head, which the coil bracket was the easiest to attach to, and since it is bolted to the cylinder head should not matter. The reason for that was because I can't see where the battery ground goes to on the frame, and weather that's solid it's under the rear bench, so running another ground was a way to troubleshoot.

I'm trouble shooting still, once I figure out what the culprit is I can go back and see what I can strengthen / make redundant... but first it has to fire...

[dcrosby]

Something that came to me as a "Wait a minute moment" part of the 12v (pink Wire system) that gets powered is a PLX Wideband O2 sensor, and it(gauge) reads normal, for what normal is when the car is not running, very lean... but is it possible that that thing wore out, and is now causing a significant voltage drain on the 12V side of things, because if I run a separate lead in parallel of 12V, I still have a voltage drop, so it's not an issue of the 12v wire being wimpy, or inadequate, and if the wideband swallowed all that voltage to try (in veign) to heat the O2 it would suck a lot of juice. It would also explain why the car ran, and died. The Wideband o2 is about 4 years old, and no wideband I've owned lasted past 2-3 years, primarily because no motor lasted that long, and I typically swapped widebands on rotary rebuilds.... and yes the car has 3 O2 Sensors, 2 Stock and 1 wideband... with heater... Maybe tomorrow I'll take that guy out of the equation....  This is really making me wish I'd made a plot of things modular plug-able instead of soldering everything, but I don't trust crimps...

A Question to people who have experience with PLX's or other Wideband O2's what happens when they go ? Or get too old besides odd readings ???

[smackhead999]

Why haven't you checked the coil wire power source?

Sorry Can you elaborate ? Where... I thought the Pink Wire was the coil wire power source... it's switched 12V... and I can't get more than 9v out of it...

Trace the source of 12V switched.  This is likely your problem.. If you arent getting enough voltage from your coils.. and it falls on its face when you demand high performance, its probably because your plugs arent firing strong enough.  Trace from the coils back to the battery.  Coils>pink wires>whatever source you got 12v switched from(probably ignition switch)>battery... its a fairly simple chain of connections.  As stated before, if your ignition switch is the source of your 12v switched, it could be faulty.  They do go bad.  Connections get loose.  If it cant deliver good current, your voltage will likely suffer... like a big resistor.

You have already done most of the work.  You found 13.4V at the battery, good.  Between 8 and 10V at the coils.  Between those two are a fuse, a few pink wires, an ignition switch, and whatever connects the the powersource from ignition switch to the battery.

[Copper280z]

Check the resistance of the pink wire from the coils to the battery post.

Also, 27 ohms is a huge amount of resistance for the ground path, fix that first.