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So, I did some more testing today. Before I drop a few hundred on a new PCM, I wanted to be sure. The MAP sensor is the only one that goes directly to the PCM. So, I started by completely isolating the MAP sensor. I checked the resistance at the MAP sensor on the VRef line to the battery, and it was 325 ohms. The ICP, EBP and CAMP, all go through the 42 pin connector on the engine. I unplugged that, and the resistance at the MAP stayed the same. The AP and Baro sensor come through the firewall connector, so I unplugged that. The resistance stayed the same. At this point, the MAP was completely isolated.
I unplugged the PCM connector, and the resistance went to an open circuit. I repositioned my multimeter and checked the resistance through the 92 pin connector (just to double check my work from yesterday). Sure enough, it was on open circuit. I checked the PCM at pin 90 to any ground and today it was at 920 ohms. That's below the spec, but still way above the 325 ohms at the MAP. I assumed the resistance dropped due to the PCM being plugged in. The only way I had to test this was to cut the wire and test it. I cut the wire and tested it with the connector plugged into the PCM, and sure enough, just on the other side of the connector, the resistance was 325 ohms going through the connector and into the PCM.
Bottom line, I pretty much confirmed my suspicions from yesterday that the PCM is my problem. Somewhere inside, pin 90 is shorted to ground. I soldered the VRef line back together and added heat shrink (not ideal, but the best I could do with the tools I had).
I can either get a reman unit from O'Reilly's, or get one from a junkyard. They are about the same price. I'm leaning towards a junk yard unit simply because I can keep my current one without the "core charge".
My question is this. Do I have to do any programming to the junkyard PCM if I get one? I know the reman units need the VIN and mileage before they'll send them to you. Do I need to have the junkyard PCM flashed with this info?
I'm a bit confused......Your MAP sensor is showing 14.7 psi in one of the pics. This is pretty much spot on for sea Level. Do you think there is a problem with the MAP sensor reading?
Also, I've had no luck with the SCT scanner reading correct EBP for my 6.0L. The EBP sensors are the same on the 6.0L & 7.3L with the same 5V reference signal. I'll go out & take a quick pic of mine.......gimme 5 min, waiting to see if the Flyers can finally score a goal.....
Yeah, the SCT tuner doesn't read EBP correctly for me either. I can hook up Auto Enginuity and DashBoss and she reads just like the MAP & Baro. But for some reason the SCT does not read EBP correctly.
You might try using Torque Pro, its free and a lot of folks on here use it and are very happy with it. You just need to buy a $15-20 OBD-II wifi adapter.
You definitely did right by replacing the EBP tube & sensor, if the tube was that bad the sensor was probably worse and the original one........
I'm not new to the site, or wrenching for that matter, I just never post anything. However, I recently picked up a 1999 F350 with 135k miles on it, and I'm working through some problems - mostly sluggish throttle response and low boost pressures. The truck has a PHP Hydra chip and I'm reading the values with a SCT X4 scanner through the OBD2 port.
I've read on here that your MAP, Baro and Exhaust back pressure values should all match. Unfortunately, mine aren't anywhere close.
I decided to take off the EBP sensor and tube to clean them. The tube looks like this:
I'm pretty sure you're not supposed to be able to see right through it. I'll be replacing it this afternoon when the parts store gets it in. However, that doesn't fix the sensor issue. I tried cleaning the EBP sensor with some brake cleaner, but it didn't help.
So, I tried a new MAP sensor, and it still shows basically the same pressure ~30 inHg. I also installed a new EBP sensor, and it shows 108 inHg.
And in PSI if you'd rather:
So, what gives? Is this a scanner issue, or is this a PCM issue? I'm kinda stumped, so any help would be greatly appreciated.
Thanks!
Kyle
Edit: after a little more research, it appears that it's more likely that I have a bad baro sensor. What do you all think?
I think your on it with your Baro sensor needing to be replaced, but the other two look fine to me.
No, they don't base readings off of one another. They're all independent. There are times when a sensor goes bad that the PCM will report an inferred value, but monitoring the sensor voltage instead of the value can sort that out. As pressure increases, the voltage from the EBP sensor also increases. With the reading you're getting from the exhaust back pressure sensor, I'd have to guess there's a short somewhere. The reading equates to roughly 4.75 volts, so it's mighty close to the VREF voltage.
Originally Posted by ff lc freak
Ok. So, most likely a bad baro sensor and a short in the EBP sensor wiring? I just checked voltage. On the EBP sensor, I'm getting 5.07 volts on the reference wire, and .07 on the other two wires koeo. At idle, I'm getting .04 volts on the other two wires. What should I be getting?
Edit: I didn't have the sensor plugged in on the numbers above. With the sensor plugged in, koeo I get:
Like Pikachu posted, the EBP voltage goes up with the increase in pressure. The Baro is opposite. Here is what I see for my 7.3L's sensor voltages & pressures here at 1400 feet elevation. KOEO, cold engine.
Keep in mind that you will need to set the chip to stock (0 setting on the Hydra) when testing the MAP to compare to Baro & EBP. Some tunes will manipulate the MAP sensor readings thus throwing you off when trying to do the Baro, MAP & EBP comparison.
Thanks WB for all your assistance. You're correct that my MAP is reading correctly. However, I did replace the Baro, and it still reads ~8.5 psi. I ran the tests I found here - ECSD - Exhaust Back Pressure (EBP) Sensor - 1994-1997 Power Stroke FAQ - that show I need at least 1000 ohms resistance between the EBP and ground, and I have ~325. That's what lead me down the rabbit hole towards the PCM. The resistance at the PCM is 325 ohms. But after reading the instructions on the test again today, I feel like banging my head against a wall. I read it as testing the harness connector, not the sensor itself. Maybe the PCM is supposed to only have 325 ohms resistance. I've been so focused on finding a short to ground, I ignored other possibilities like the SCT scanner not reading correctly. It didn't help that I misread the instructions.
I think my next step is to get Torque Pro and hopefully start reading the correct values on my sensors. Hopefully, that is all that is going on.
Thanks WB for all your assistance. You're correct that my MAP is reading correctly. However, I did replace the Baro, and it still reads ~8.5 psi. I ran the tests I found here - ECSD - Exhaust Back Pressure (EBP) Sensor - 1994-1997 Power Stroke FAQ - that show I need at least 1000 ohms resistance between the EBP and ground, and I have ~325. That's what lead me down the rabbit hole towards the PCM. The resistance at the PCM is 325 ohms. But after reading the instructions on the test again today, I feel like banging my head against a wall. I read it as testing the harness connector, not the sensor itself. Maybe the PCM is supposed to only have 325 ohms resistance. I've been so focused on finding a short to ground, I ignored other possibilities like the SCT scanner not reading correctly. It didn't help that I misread the instructions.
I think my next step is to get Torque Pro and hopefully start reading the correct values on my sensors. Hopefully, that is all that is going on.
Here is a link to the more specifics on the Baro Sensor instead of using the EBP guidlines.
I believe your EBP sensor is fine, I have no hands-on experience using the SCT tuner on a 7.3L, but I ran into the same problems and readings you posted on my 6.0L with the same exact sensor (both models use the same sensor and 5V Ref voltage), while Auto Enginuity & DashBoss would show the correct readings.
Right now your truck PCM thinks it at about 10,000 foot elevation - if the Baro readings on the SCT are correct. But I don't trust using the SCT for diagnosing - just my experience from chasing that rabbit and banging my head previously.
1. What voltages are you reading from your Baro sensor?
2. Have you tried wiring up your old MAP sensor to the Baro wires since it will basically function the same? If the PCM see's Baro readings out of wack it will use the MAP.
the PCM will use the MAP sensor readings if the Baro signal failed. Then it will use a set value of 29.61 in hg (14.54 psi) if both the MAP and Baro readings failed. You could disconnect both the MAP and the Baro sensors and verify the 29.61 in hg reading from the SCT tuner, or disconnect the Baro and verify the same readings for the MAP & Baro. If not - then the SCT is not displaying the correct value.
Also, if the Baro sensor voltages are too low or too high a code should be set, and yes - the SCT tuner isn't the greatest code reader in my limited experience with it.
Diagnostic Trouble Code Descriptions
0108 = Signal voltage was greater than 4.9 volts for more than .2 seconds
0107 = Signal voltage was less than .04 volts for more than .2 seconds
You should see some codes after pulling the MAP & Baro sensors. If not, sit back and drink a beer until you get TorquePro, Auto Enginuity, NGS or something like that.
also, check out this thread - this guy also thought it was his PCM, got a new one and it didn't help. Just want to rule out the sensors & diagnostic tols before you go PCM hunting........
Does she seem way under powered? Not building much boost? The PCM will hold her back with those low Baro pressure readings.
Sorry to post so much, but just to make sure I didn't confuse you, myself or others. This is what I think you should try - the best part it takes about 5 min and it's free.....
hook up the SCT scanner and read Baro, MAP & EBP.
Disconnect the EBP sensor, the PCM should default to a reading of 43.5 PSI, 300 kPa or 88.6 in HG depending on what unit you choose. You should see a fault code - P0472. Note: if the PCM does not receive a signal from the EBP sensor it will not engage the EBP valve. So during cold starts after the 2 min (or when the glow plugs go off) the the high pitch exhaust sound will not be present like it is when the EBPV is activated.
Disconnect the Baro Sensor and it should read the same as the connected MAP sensor. You should get a fault code - P0107.
Disconnect the MAP sensor and you should set a P0237 code and go to a default of about 14.6
If the SCT doesn't show this then I would wait until you get a better scanner/code reader, or you'll just be running in circles.
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I read it as testing the harness connector, not the sensor itself. Maybe the PCM is supposed to only have 325 ohms resistance. I've been so focused on finding a short to ground, I ignored other possibilities like the SCT scanner not reading correctly. It didn't help that I misread the instructions.
