Engine Ground Leads - How Many?

[fsuguy]

Does anyone have a clear idea of how many ground leads the '92 LS400 engine has, and where they all are? I would dearly like to know this information, if possible!

thx

[curiousB]

Didn't see a diagram for your model but my year '04 has two "Bond Cables" as they are called.

[fsuguy]

curiousB,

Thank you for posting this pic. I don't think it should be significantly different for the earlier models. You are wealth of information, and I, for one, and very, very glad you are a member of this forum and share your experience and knowledge with the rest of us!!

[landar]

I actually have a 92 that is fairly unmolested so maybe I could open the hood and take a look. In general, all cars have at least two or three ground straps. There is a fairly small cable, usually a wire weave attached to the back of the block and to the chassis firewall. Then there is a much larger cable (like #2 or greater gauge) bolted directly into the block. This ground cable supplies the much higher currents needed for the starter which has inrush requirements > 100 amp. This larger cable must go directly to the (-) battery post. Another important ground is to the alternator. This ground can come thru the mounting bolts or more directly thru the wire harness.

Out of curiosity, why do you ask? Are you having some problems?

[pj8708]

curiousB,

Thank you for posting this pic. I don't think it should be significantly different for the earlier models. You are wealth of information, and I, for one, and very, very glad you are a member of this forum and share your experience and knowledge with the rest of us!!

Ditto to CuriousB & Landar.

[924S]

Thanks for posting the image.

But...

I need to know what's involved in replacing the negative cable. In my (lurking) research every request for this information is met with "Why" and a seeming reluctance to answer.

Where is the other end of the negative cable? and what's involved with replacing it? [94 LS400]

I am new to Lexus, but not to cars. This is my wife's car; mine is a 1987 Porsche 924S that I am slowly bring back to better days (it is a very reliable daily driver).

[fsuguy]

landar (and curiousB, and Paul A),

Thanks for asking... in a previous posting, someone suggested that occasional hesitation may be due to a loose ground wire in the engine bay. I know from my own experience with a '86 Honda Prelude that this is very possible - a ground lead at the end of the fuel rail was loose on the Honda, which caused all sorts of diagnostic issues, since everything else worked perfectly. Finally, entire bolt came off and I could see sparks from the loose ground wire when it made contact with the fuel rail. Once I replaced the bolt, everything was smooth sailing again, but it was devil to diagnose until I knew where the problem lay.

With my '92 LS, I don't have any MIL/CEL lights, and do have what I can only describe as a sort of hesitation on occasion - sort of a dropping out of gear, or engine cut out, or fuel interruption (something like that, but not exactly sure, since RPMs don't drop to 0) - it is not a violent shudder - just as if the car is coasting to a stop, then it resumes as if nothing is wrong, unless I immediately step on the gas, then there is a slightly noticeable shock of engagement, as if something is forcing the engine or transmission to engage(?) This behavior only began after I had a Toyota dealership (Thomasville Toyouta in Georgia - the closest dealership with whom I have not had a lousy repair/maintenance experience) change my valve cover gaskets and fix a leak in the rear water bypass; they did a pretty bad job, since the insulation on the rear wiring harness under the heater control valve was not replaced, bolts were not replaced, and the hose to the water heater valve was tightened to the point where it was cut through and leaked water all over the harness (I had to get a new hose and clamps from Sewell and fixed it myself!)

For what it's worth, as part of my routine maintenance I have had the water pump, timing belt, rotors, caps, wires, and plugs changed. I also changed the fuel pump resistor, both coils (coils went bad at different times), TPS (it went bad as indicated by Cruise control failing to hold), water outlet and thermostat, serpentine belt; so none of these can be the culprit, at least I am hoping so. Also had the transmission rebuilt, and replaced solenoids #1 and #2 to fix shifting problems.

I have, after much searching, managed to find a M12 double banjo bolt and union (ntxtools.com) and plan on testing my fuel pressure and regulator to rule those out as a possible cause. If it is fuel related, I think I may also need to test my fuel pump relay. One additional helpful note - When the cruise control is engaged, the problem does not manifest itself(?) So if any of you think the ground may be a solution, or anything else, I would appreciate it very much.

...and 924S, just want to point out that often posters asking for help on this forum don't always explain the problem they are having, so asking why is intended to elicit more background information on the problem that usually helps those who may have very useful information relevant to the problem not provide incorrect solutions; at least that is my experience, so don't think of it as reluctance.

[curiousB]

Ground wires or intermittents could result in strange behavior that is difficult to diagnose. There is a known problem with the cable harness in the rear trunk hinge on some of these models. A broken wire inside its plastic jacket is not a visible defect yet can create havoc with intermittencies.

As a test you could try adding an extra wire from the negative post of the battery to a good ground point on the engine. Extra grounds won’t hurt anything. See if it makes the problems go away. If you don’t see any improvement just take it off. Just don’t leave it flopping around under the hood. Use some wire ties and secure every 4-6 inches or so it doesn’t move around or get caught in any moving parts.

I'd flush out the hingle harness theory first though because it is a well documented problem. Just search this forum and you'll get numerous hits on that.

[landar]

Thanks for the explanation, fsuguy. I think it does help. Gives us background context and perhaps we can provide better assistance. Seeing that none of us are being paid for our time or advice, I think it reasonable to ask 'why'.

You mention perhaps a most salient point, that is, the car seems to run fine with cruise control. Makes me almost think it is still TPS related. Apparently the TPS is a temperamental beast and requires some adjustment to get it working right. See this tutorial and ponder -> http://www.lexls.com/tutorials/EFI/tps.html

As concerns grounds or any electrical connection for that matter...yes, they can become intermittent and cause all kinds of hair pulling results. It does not even have to be a ground connection. Every electrical connection on the engine can become intermittent over time. The mechanic that worked on your vehicle may have inadvertently left a connection loose or not fully pushed back together. The TPS connector could even be suspect. You might want to re-examine the connectors in this area and take them apart, examine for dirt, corrosion, squirt some contact cleaner in there and put them back together.

I have seen all kinds of connector problems over time. Even connections that you would swear are fine and that look fine from the outside, may not be.

[fsuguy]

landar,

Thank you for the link and explanation... also, now that you mention it, the locking tabs on the TPS connector did break off and I have used electrical tape to hold it in place - that may be my problem!! I think I will get another new TPS, though, just to be certain. Any ideas on where I can get replacement harness connectors for the TPS?

curiousB, that is a good idea - to put in another ground - will do that and post any findings. I had gone through the trunk hinge harness and repaired a couple of broken wires that fixed a couple of other problems. It was a chore trying to find the broken wires inside the insulators, but I finally hit on the idea of using a simple continuity probe - the one with the sharp point on one end and an alligator clip on the other - worked like a charm! Did not find more than three broken wires (two yellow and one white).

[924S]

I managed to save myself the job of replacing the cable at least until we have warmer weather**. I bought a battery cable splice and used that after cuttting off the truly messed up 1st 6 inches, stripping off about 1/2" of the covering. The barrel slipped over the good cable, after dressing it up nice, and clamped it down. The band/loop battery clamp went on tightly.

The car started right up and my wife have gone to work with for two days without a hitch. I also have noticed that the what working lights we have are brighter, and the starter no longer sounds reluctent to go to work; it now comes awake and turns over with atacrity.

**I had 7 kids when we bought the house so the garage was sacrificed to bedrooms, office and homeschool. Now there's only our 14yo left home. I hope to reclain the garage next summer as part of a overall refresh of the house. Also, I am a bit slower working on anything after a stroke last summer - but I am back to working part time at home and living fairly well. [i don't recommend this just 'cuz you want to experience an 80 mile helicopter ride]

Edited December 17, 2011 by 924S

[924S]

NOW, I have a new thing. My wife mentioned that it started to "rumble" getting worse as she drove then suddenly sounded to her that it a plugged pipe had blown open (her description of the sound) and it ran fine.

Today, I took it out for some errands, all in town. When leaving the driveway, it seemed reticent to move, as if the brakes were hanging up. 3 stops, longest leg about 2 miles back to home. It's behaviour degraded to the poind that it felt like I had a flat tire complete with the tire flopping sound and the car was shuddering badtly. The last leg was about a mile on the hiway which I took slow, about 45, which was interesting.

I checked the wheels for heat - none, There was the smell of hot rubber...

No flat.

Where would you start?

[landar]

NOW, I have a new thing. My wife mentioned that it started to "rumble" getting worse as she drove then suddenly sounded to her that it a plugged pipe had blown open (her description of the sound) and it ran fine.

Today, I took it out for some errands, all in town. When leaving the driveway, it seemed reticent to move, as if the brakes were hanging up. 3 stops, longest leg about 2 miles back to home. It's behaviour degraded to the poind that it felt like I had a flat tire complete with the tire flopping sound and the car was shuddering badtly. The last leg was about a mile on the hiway which I took slow, about 45, which was interesting.

I checked the wheels for heat - none, There was the smell of hot rubber...

No flat.

Where would you start?

Where would I start? At the beginning, of course! B) If you can (sorry to hear about your stroke, btw), jack up the front of the car and try rotating each tire by hand. There should NOT be any significant resistance or grinding/grating noises other than perhaps the faint sound of the discs rubbing against the rotor, which is normal. Then jack up the back and try those tires/wheels. My thinking here is that you may have a dragging brake(s) or bad wheel bearing.

[curiousB]

You can evaluate front bears by driving at 15-20 MPH and make a waving back and forth drive down the road (open road with no one around that is). If one of the front bearings is bad it should make more noise when it is loaded. The more the car is leaning to that bearing. When you turn the other way that same bearing will be lightly loaded and shoud be more quiet.

[pj8708]

Just a question for my own learning curve. Would the bearings or brake drag account for the burnt rubber smell, or the "plugged pipe had blown open?"...(my wife talks that way too.)

Thanks

[924S]

Just a question for my own learning curve. Would the bearings or brake drag account for the burnt rubber smell, or the "plugged pipe had blown open?"...(my wife talks that way too.)

Thanks

Exactly my question. It takes me a while to do much of the car stuff, but the Dr. thinks it's a good physical therapy.

I've never encountered this group of symptoms.