Limp mode problems

[Demetre94]

What’s up everyone. I have a 05 s197 4.6L. A couple weeks ago the battery was grounded while trying to tighten the cable. From that moment, my car started going into limp mode. Wasn’t having the problem before. So I replaced the TB since I had a warranty through autozone, fixed nothing. Decided to replace the pedal too, just because it was cheap from the junkyard, same problems. It’s improved lately, I can drive the car for 40+ mins sometimes, then all of a sudden it goes into limp mode. I also did a live date while driving, and the MAF sensor is literally registering nothing.

 

[86GT351]

You probably popped the master fuse attached to the battery cable when you grounded it.

 

[Demetre94]

Is this main fuse connected to the negative line closer to the battery? I haven’t seen this fuse before. There was a lot done to my car before I go hold of it.

 

[DieHarder]

You probably popped the master fuse attached to the battery cable when you grounded it.

View attachment 116212

If he popped a 200A battery fuse the car shouldn't run at all. i.e. No B+. Shouldn't even be able to crank it.

Got a VOM (Volt/Ohm Meter)? What is your DC voltage (across the battery with engine running)? Any codes?

 

[Demetre94]

The battery is healthy when the car is off, and at idle. I replaced it after the spark event. It seems like things freak out under load. The codes I have are p0102 and p2110. But MAF is brand new, literally.

 

[Demetre94]

Also, just yesterday I was having problems starting. I’d turn the key and all the dash lights would flicker, or it the dash lights without be super dim as if there was barely power. Then I was at a stop light and the car died at idle out of nowhere

 

[Midlife Crises]

Some or all of the battery cables and or ground straps are probably corroded, loose, faulty or missing. That is the most common cause of voltage drop under load. These vehicles are very sensitive to low voltage.

 

[Demetre94]

Some or all of the battery cables and or ground straps are probably corroded, loose, faulty or missing. That is the most common cause of voltage drop under load. These vehicles are very sensitive to low voltage.

Do you think the spark I had from grounding the battery could’ve caused all of the wires/ground points to go bad? I wasn’t having any problems before that.

 

[Midlife Crises]

I would not say all the connections would go bad at once. They do fail over time. The connection that was carrying the most current when you had that short circuit making sparks certainly could have been damaged.
To me, what you describe sounds like voltage drop do to bad connections. I would disconnect, clean and reconnect all of the battery cables at both ends. Look for damage. Use a wire brush and sand paper to get clean metal to metal contact. Use Electric motor cleaner to get rid of oil and grease in the connections. If you see corrosion growing inside the cables, replace them.

 

[Demetre94]

Thank you, I changed the wire running from alternator to battery, a new battery and new connectors for the terminals. That seems to have solved my starting issue. What’s your opinion on my limp mode problem?

 

[Kev555]

You need to check as much of your wiring loom as possible for melted wires. That sounds like burnt/melted connection symptoms where it eventually looses connection while driving and throwing limp mode . Its possible you burnt a connection on the ECU board as I've seen this happen on other types of vehicles. The power surge also could have fried the MAF. You will find the fault I'm sure if you keep checking components out one by one. Also double check that fuse 86GT mentioned.

 

[Pentalab]

Get a DVM...and put it across the battery terminals. Should be aprx 12.4 vdc with eng off. With eng on....and idling, should be in the 14.7 vdc range. If it's still 12.XX, your alternator is dead.

Switch DVM to read ACV. should be a few Millivolts at most. If it's more than that, like several volts of AC, you have diodes shorted inside the alternator.

 

[Demetre94]

Get a DVM...and put it across the battery terminals. Should be aprx 12.4 vdc with eng off. With eng on....and idling, should be in the 14.7 vdc range. If it's still 12.XX, your alternator is dead.

Switch DVM to read ACV. should be a few Millivolts at most. If it's more than that, like several volts of AC, you have diodes shorted inside the alternator.

Could a bad alternator be giving me MAF codes? I replaced the MAF and even got a junkyard ecu, and it changed nothing. If it is a burnt wire, is it worth pulling the harness and stripping it to find the wire? Or get a different harness?

 

[Kev555]

Id say check your own harness first before changing it out as I think its a big job. Stick to the smaller straight forward stuff first. Sometimes if you cant find an electrical issue get an auto spark to diagnose it if you can afford that. How long did the short last in seconds? Check out any components mentioned by other members on here first. Midlife Crisis hit on an important one too about voltage drops, that can play havoc producing a lot of different codes at random. If it still only replicating the MAF code stick to diagnosing and exhausting all avenues in that particular circuit first. Great to see its not looking like the ECU. I might have missed your post but did u try a new MAF since the battery short?

 

[Laga]

Check the ground to the MAF. It is on passenger side next to top radiator support. Here is a photo of mine. Disregard wires on left. Those are for aftermarket add ons. They are black wires when stock. These are a different color because the corrosion was where the wire joins the eyelet connection. I replaced the connection with crimp and heat shrink and glue fittings. This is also the ground point for the ECM. After 21 years, can’t hurt to check all ground points.

 

[Demetre94]

Id say check your own harness first before changing it out as I think its a big job. Stick to the smaller straight forward stuff first. Sometimes if you cant find an electrical issue get an auto spark to diagnose it if you can afford that. How long did the short last in seconds? Check out any components mentioned by other members on here first. Midlife Crisis hit on an important one too about voltage drops, that can play havoc producing a lot of different codes at random. If it still only replicating the MAF code stick to diagnosing and exhausting all avenues in that particular circuit first. Great to see its not looking like the ECU. I might have missed your post but did u try a new MAF since the battery short?

Thanks for the advice! Yes I did replace the MAF after the spark. The spark was very short, but it was a pretty big spark. When I hooked up my scanner and looked at the live data, the MAF wasn’t registering anything at all. Do you think the suspect could be the sensor wire? I’m just trying to narrow down what wires I should follow.

 

[Demetre94]

Check the ground to the MAF. It is on passenger side next to top radiator support. Here is a photo of mine. Disregard wires on left. Those are for aftermarket add ons. They are black wires when stock. These are a different color because the corrosion was where the wire joins the eyelet connection. I replaced the connection with crimp and heat shrink and glue fittings. This is also the ground point for the ECM. After 21 years, can’t hurt to check all ground points.

View attachment 116277

Thank you! I’m going to check that today

 

[Kev555]

Thanks for the advice! Yes I did replace the MAF after the spark. The spark was very short, but it was a pretty big spark. When I hooked up my scanner and looked at the live data, the MAF wasn’t registering anything at all. Do you think the suspect could be the sensor wire? I’m just trying to narrow down what wires I should follow.

Just to make sure we haven't got crossed wires here(Parden the pun) when you fitted the new MAF after the shorting incident the new MAF still registered no data on your diagnostic? Is the diagnostic tool picking up data from other sensors?

 

[Juice]

Make sure you are monitoring the correct MAF parameter. You want 'MAF volts' change with rpm/throttle input, just to see if MAF working.

 

[Demetre94]

Just to make sure we haven't got crossed wires here(Parden the pun) when you fitted the new MAF after the shorting incident the new MAF still registered no data on your diagnostic? Is the diagnostic tool picking up data from other sensors?

lol nice. But i never tested the old MAF sensor, i seen the code and figured id just replace it. Then thats when I started jumping into the scanner. The scanner is picking up other sensors like pedal position, throttle position etc