Chasing an electrical ghost in the wiring! - MR2 Owners Club Message Board
 
LinkBack Thread Tools
post #1 of 13 (permalink) Old August 21st, 2019, 09:07 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Chasing an electrical ghost in the wiring!

I started a different thread on testing the TPS, not realizing I was chasing a ghost (intermittent electrical issue). I had one of these ghosts in the distant past, but not to this extent. I build other cars for a living, so I see my fair share of odd issues, but I thought I would share this story because it is one of the more challenging problems I've encountered to date, and it represents the extremity of what can happen with old cars (nearly 30 years old now) and how valuable having spare parts for diagnostics can be. This is six straight days of diagnostics.

==
I had the car sitting in the garage at my home for about a year. I probably only started it three times in that time period. Last month I decided to register it and put it on the road. I noticed the idle was high. I looked at all the usual suspects...loose connectors in the engine bay, vacuum leaks, etc. Last year I was testing an ECU Masters DET3 piggyback computer (since disconnected, but present) so I have a custom wiring harness installed that I built. I wiggled the wires a little bit. Nothing helped.

I drove it down to my shop (about 10 miles). It drove just fine.

I found a leak in the EGR valve, so I removed it and blocked it off.

After reassembling everything, I noticed the engine was running really badly. Almost like it was running on three cylinders or when the distributor cap gets water in it (like after washing the engine bay and having some "wet" running issues).

I started into checking things more thoroughly...
I checked to make sure all four cylinders had spark and fuel. All four spark plug wires were arcing if I removed the boot from the plug. All four injector connectors had 12V with the key on.

I checked for codes...
I had a code 51 present, but only while the the engine was running with the check connector jumped, and I was revving the engine. After I let off the throttle, the code would go away (normal as per the BGB). The BGB says says code 51 can be an issue with the IDL signal from the TPS, so I spent a lot of time chasing down issues with TPS adjustments. Nothing changed.

I started changing out components with spare parts I have laying around...
1. Spark Plug Wires
2. Dist Cap
3. Rotor
4. Distributor (3 of them)
5. Coil
6. Igniter
7. Coil Wire
8. Injector Resistor Pack
9. BOV
10. ECU
11. AFM
12. Cruise Control ECU (it's connected to the IDL signal too).
13. TPS (3 of them)

I looked for more vacuum leaks.

I compression tested the engine.

I looked for flat cam lobes (rare)

I looked for missing shims in the head.

I continuity checked all the wiring.

I tested the injectors for resistance. All had 3.1 ohms.

Everything and everything checked out.

FINALLY (and I should have done this right away, instead of 5 days later)...
I took it for a spirited drive, and did some low boosting, instead of just letting it run (crappy) at idle and revving it up in the garage.
I pulled the spark plugs again and found number 2 to be covered in black soot; though it was completely dry. Weird.
Then, I pulled each of the injectors while the engine was running and after pulling cylinder #2, there was no difference in how the engine was running! Holy moly! I repeated this with the spark plug wire on cylinder #2. Same thing! (I hadn't noticed this behavior before when I was checking for spark).

Turns out cylinder #2 is not firing. Why?! The wiring to the injector checks out. I tested the spark plug - I pulled it out and grounded it to something metal on the engine. It's sparking. I swapped it with the spark plug in cylinder #1. Cylinder #1 still runs fine and cylinder #2 still doesn't fire.

It must be the 2nd cylinder injector. I pulled the connector and put voltage to the 2nd injector (with a spare battery)...it clicks fine. WTF?

I tried listening to each injector with a long screw driver as described in the BGB, but I found it was difficult to discern whether or not the clicking I heard was from the injector I was closest to, or simply the sounds from the nearby injectors transmitting through the fuel rail.

I decided to swap the #2 injector, thinking it could be "locking up" in the open position. No change after swapping the injector.

Then, I decided to disconnect injector #2, and connect a spare loose injector and start the engine. I was holding the injector in my hand and it was not clicking! WTF!?

So, I figured the injector was likely stuck on. So, I tried a couple more injectors. Same thing! So, the problem could possibly be the injector is staying grounded all the time, rather than only grounded when it's supposed to fire (it always has 12V power to the injector and the ECU connects the ground to fire it when it's supposed to). This is why it seems to run fine when I first start it up, but after a few minutes, cylinder #2 drops out. I think this is because the #2 injector is firing all the time and over-fueling the cylinder to the point it won't actually combust.

I checked the wiring for a shorting ground (to the body) to the injector wire in the harness. I can't find one.
Then, after talking with a friend last night, he suggested I could actually be having an intermittent high side (12V) wiring issue, not the ground. I'm not sure that makes sense, given the behavior, but I'll check the hot side wires going from the injectors into the injector resistor pack (that's where the other injector wire goes). So, I'll be chasing the wiring yet again today. Hopefully finding the intermittent wiring issue.

After all was said and done yesterday, I ended up NOT having the problem anymore after I manipulated all the wiring again. There is a ghost in there somewhere!!!

This is all pretty interesting because it shows what can happen with old wiring baking in a hot garage for a summer; not to mention I have tapped into several of the wires in the engine harness (at the ECU) over the 20 years I've owned this car. I probably need a new wiring harness.

Something to keep in mind...the "intermittent" nature of issues. Sometimes these can be tough to find.

Last edited by SpdDm0n; August 22nd, 2019 at 07:02.
SpdDm0n is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old August 22nd, 2019, 07:16 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
UPDATE: I found the short yesterday! I was putting everything back together so I could get the car out of the shop (I needed the space for other cars), and as soon as I had it all together, I started the engine. It ran great, but the idle was high again. I realized I left the TPS connector disconnected (this will advance timing and raise the idle), so I reconnected it. It immediately started to run badly again! WTF?! I looked at the connector and found another broken wire. They are breaking right at the connector, so it's not a simple solder job.

I pulled the pin from the connector, trimmed it, and began to solder the wire to the pin (this is only a work-around - you really need a new pin, new weather pack around the pin, and a proper crimp tool to repair these). I had a hard time getting the pin back into the connector with the additional girth to the pin, so I had hoped it would work long enough to get the car back to my house for storage.

I reconnected it and started it up and it still ran like crap. I began to try and push the pin further into the connector, when I realized i would break a third wire, so I simply removed that wire and repaired it also. I fixed three wires and let the 4th, as it seemed it would last until I could properly repair the whole harness.

I connected the connector and it still ran crappy! Then it dawned on me!!!!!! The first wire that had broken in the connector days ago is BROWN. The brown wires in the connectors at the ECU are the ground wires! I was looking for a ground wire that was likely grounding the injector prematurely. I would also likely be grounding to the body somewhere if my theory was correct. I checked the injector wire for continuity to the body. BOOM!!!! I had continuity from the injector wire to the body! Holy moly!

So, without physically seeing the short yet, I know it is in the part of the harness that joins the TPS and the injectors. That's nicely buried in the black plastic sheath that encases all the wires that travel along the internal curve of the intake manifold next to the fuel rail. That will not be as easy place to get to to repair, but at least I know where the short is. Ya!!!!

Holy cow. That was a whirlwind of a process finding a ghost!!
SpdDm0n is offline  
post #3 of 13 (permalink) Old August 22nd, 2019, 08:29
Registered User
 
Join Date: Apr 2008
Location: Thornton, Co
Posts: 573
OldTrader Rating: (6)
Hey, I am here in Thornton. I think I have a TPS sensor with four inches of wires laying around you can have for free. Shoot me a PM. My original TPS sensor wires broke and I had to cut and splice it together. It works really good and the car has been running fine.
duckfamily is offline  
Sponsored Links
Advertisement
 
post #4 of 13 (permalink) Old August 22nd, 2019, 09:27 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Quote:
Originally Posted by duckfamily View Post
Hey, I am here in Thornton. I think I have a TPS sensor with four inches of wires laying around you can have for free. Shoot me a PM. My original TPS sensor wires broke and I had to cut and splice it together. It works really good and the car has been running fine.
Wow! That would be great! Thank you! Of all the extra parts I have laying around...I don't have another engine wiring harness. It would be great to have your pigtail. That would be really nice. Thank you!

I'll PM you from my other account. This one has a full inbox and I have a lot of information in my messages and I don't have time to delete them.

Thanks again!!
SpdDm0n is offline  
post #5 of 13 (permalink) Old August 22nd, 2019, 16:19
Registered User
 
Join Date: Jan 2006
Location: Alexandra, New Zealand
Age: 59
Posts: 7,422
OldTrader Rating: (3)
There are several examples of failed harness faults on the UK forum. Seems the OEM harness has several joins that can corrode and break due to sub standard protection from moisture entering. One such thread I am following had the owner pull whole harness to locate and repair all the factory joins. He has examples of the joins and location within harness that could be of some use.

Factory joins could be your problem or even the wire taps used. I'm not a fan of wire taps as they cut into the core material and eventually cause issues (loose tension or limit current capacity of parent wire). They are a nice convenient splice to use but hardly ever last the distance. I'd recommend finding and replacing with a correct splice or soldering.

If you can get into this thread it may be worth reading through.

https://www.mr2oc.co.uk/forum/41/167671.html
benckj is online now  
post #6 of 13 (permalink) Old August 23rd, 2019, 19:35
Registered User
 
Join Date: Jun 2005
Location: Everett Washington
Age: 59
Posts: 1,992
OldTrader Rating: (20)
FWIW: I think you did a fabulous job of troubleshooting. Way cool!
sarnodude is offline  
post #7 of 13 (permalink) Old August 24th, 2019, 13:16 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Quote:
Originally Posted by sarnodude View Post
FWIW: I think you did a fabulous job of troubleshooting. Way cool!
Thanks! This one is tough. Just when I think I have it solved, I don't. I may have more than one issue that are not related. I'm still at it. Hopefully find the problem(s) soon!
SpdDm0n is offline  
post #8 of 13 (permalink) Old August 25th, 2019, 12:45
Registered User
 
Join Date: May 2013
Age: 32
Posts: 58
OldTrader Rating: (0)
Wow that's a tricky one. Nice job finding it. It might be worth your time to pull the wiring out and refresh the loom with new wires and splice points so you won't have this issue ever again.
Kremling is offline  
post #9 of 13 (permalink) Old August 26th, 2019, 08:09 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Quote:
Originally Posted by benckj View Post
There are several examples of failed harness faults on the UK forum. Seems the OEM harness has several joins that can corrode and break due to sub standard protection from moisture entering. One such thread I am following had the owner pull whole harness to locate and repair all the factory joins. He has examples of the joins and location within harness that could be of some use.

Factory joins could be your problem or even the wire taps used. I'm not a fan of wire taps as they cut into the core material and eventually cause issues (loose tension or limit current capacity of parent wire). They are a nice convenient splice to use but hardly ever last the distance. I'd recommend finding and replacing with a correct splice or soldering.

If you can get into this thread it may be worth reading through.

https://www.mr2oc.co.uk/forum/41/167671.html
Thanks for the link. Ugh. Yeah, chasing these issues have been a real challenge, especially when they are intermittent or have multiple sets of related behaviors, given different operating conditions. I went back and retested many things I already tested in the past, when I determined a different operating condition that is relevant. Some tests are not showing the same results after I go back and repeat the tests. I've adjusted the TPS multiple times again, even using an old analog ohmmeter to watch for that slight "deflection".

I used a noid light to try and see the difference on the injector wires, but the lights are so dimly lit, you can barely see them. They get brighter as the engine is revved up, and cylinder #2 appears to behave the same as cylinder #1, so now I'm not sure if there is an issue with the injector firing after all. I did replace the ground wire to the ECU from the injector (ran a separate wire), but that didn't change the behavior either. I misdiagnosed the ground wire continuity to the body ground. Turns out this new multi-meter fooled me again. It responds audibly with a continuity "beep" with any resistance under about 50 ohms. I didn't realize I still had the injector wiring connected to the injector, so the test was invalid, since the positive side of the circuit continues through the injector, injector resistor pack, and so on.

I still couldn't determine, consistently, if there is there is an over fueling issue. The injector seems to be firing as expected, visually, when compared to the other cylinders with the noid light, at least when revved up. I probably need a o-scope to better determine if there is an issue with the operation of the pintle in the injector. I suppose I could have replaced the injector with another bad injector and the pintle is sticking on both injectors, but it runs well at times.

Also, either by allowing some running *time* the engine, or *heat* generated in the engine over the warm up period is causing the engine to behave differently, intermittently. I checked the water temp sensor. It seems to be operating in range. I also know I had the cold start injector disconnected for one test (and I forgot I did that), so that confused the results of the next test.

The only repeatable behavior I seem to have is bad engine running condition when the TPS is connected. I know the ECU is advancing timing and raising the idle (idle increase either directly, or as a result of the increased timing) when the connector is disconnected, but I had a hard time determining if there was a third engine running condition (bad) when the TPS is disconnected, but only when warm. ?? But, I may have confused that test with the cold start injector being disconnected (forgot). Ugh.

I am able to see the Air Fuel ratio is lean when the injector is disconnected, and a little too rich when the injector is connected. Fueling seems to be ok. Hmmm..why did I identify cylinder #2 having an issue? Maybe I had multiple issues and I didn't know it. Maybe I'm solving them one at a time. ??
SpdDm0n is offline  
post #10 of 13 (permalink) Old August 26th, 2019, 18:35
Lifetime Gold
 
Join Date: Jan 2007
Location: Ithaca, NY
Age: 67
Posts: 11,678
OldTrader Rating: (3)
Quote:
Originally Posted by SpdDm0n View Post
... I misdiagnosed the ground wire continuity to the body ground. Turns out this new multi-meter fooled me again. It responds audibly with a continuity "beep" with any resistance under about 50 ohms...
Good point. A continuity test tells you less than nothing unless you know what you are expecting to measure and what your meter is telling you. Generally, continuity testing is only useful on an isolated component. Testing in circuit is usually pointless for two reasons: There are almost always multiple paths that one doesn't think of, and for a power circuit, a multimeter has nowhere near the sensitivity to give a meaningful measurement. The best way to test a power circuit is to power it up and measure voltages across connections or relative to chassis.
rmeller is offline  
post #11 of 13 (permalink) Old August 27th, 2019, 03:53
Registered User
 
Join Date: Jan 2006
Location: Alexandra, New Zealand
Age: 59
Posts: 7,422
OldTrader Rating: (3)
Electrical circuits can be very tricky to diagnose until you can break them into seperate circuits and understand each component. Having a unreliable multimeter only adds to the confusion. Just try and be methodical with your approach and donít jump to conclusions.
benckj is online now  
post #12 of 13 (permalink) Old August 27th, 2019, 08:20 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Quote:
Originally Posted by Kremling View Post
Wow that's a tricky one. Nice job finding it. It might be worth your time to pull the wiring out and refresh the loom with new wires and splice points so you won't have this issue ever again.
Thanks. As is turns out...I no longer have an electrical issue at all. Wow. WTF?! This is the most confusing issue I've ever encountered on this car. After I could no longer consistently repeat each running condition with specific tests, except disconnecting the TPS and the engine running condition appearing to *improve* (this is likely just the ECU advancing timing and idle speed, nothing more - which is normal), I found something really weird on accident!!!

I found that the bad running condition was *improved* to normal running condition, when I simply pulled the EFI fuse and reset the ECU! Then, whether the engine was cold or warm, and the TPS is connected or not...if I open the throttle all the way (full-open throttle), just once, even just quickly from an idle (no engine load), immediately, I have a bad engine running condition! This is repeatable every time! Wow!

Now, to make matters even more confusing....
I decided to take the car for a drive (most of this testing has been in the shop at idle), drive it easy with hardly any throttle...
I can rev it up to 6K RPM, with barely any throttle open, and the engine continues to run fine.
I then decided to give it some throttle and boost. The ignition felt like it was breaking up a bit. Hesitating, sputtering...then, boom! A big blast of smoke came out of the back, and the car was running great! WTF?!

Now, the engine runs good ALL THE TIME! I can't repeat the bad running condition...even with full throttle!

Now, I'm back to the original reason I removed the throttle body (looking at the ISC valve) in the first place (high idle).

Last edited by SpdDm0n; August 27th, 2019 at 08:25.
SpdDm0n is offline  
post #13 of 13 (permalink) Old August 27th, 2019, 08:25 Thread Starter
Registered User
 
Join Date: Mar 2004
Location: Loveland, CO
Posts: 654
OldTrader Rating: (1)
Quote:
Originally Posted by benckj View Post
Electrical circuits can be very tricky to diagnose until you can break them into seperate circuits and understand each component. Having a unreliable multimeter only adds to the confusion. Just try and be methodical with your approach and donít jump to conclusions.
Very good advice. I think I got caught in the weeds on this one and lost some of my own basic login in my testing. I'm also getting a new meter. I don't like this auto-ranging crap.
SpdDm0n is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MR2 Owners Club Message Board forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: (0 members)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome