So, I've thought I've had this problem licked a few times now, only to have it rear its head again a few days later. so, I've waited a week after my latest 'fix' and the problem has yet to come back - hopefully i'm in the clear.

the short version of the story is: I bought my CC with a known power-loss/bog-down problem (it was too good a deal to pass up). figured, worst case, i'd swap the engine in from my other truck, best case, I figure it out. the previous owner said it was throwing a bad boost/MAP sensor code, so he replace the MAP, but had no improvement. he was convinced it needed a new PCM, but with the mileage on the truck (354k) and other things needed, he decided just to cut his losses and sell. I tried a bunch of things (all of which, frustratingly seemed to work for a day or so, but they the problem would come back) and eventually swapped in the BARO sensor from my [now] parts truck and this beast roared to life like it had never done since I owned it. makes 15 psi of boost easy now and flies down the road.

OK - the long version of the story for whoever's interested/following a similar problem. for the first month I owned the truck, it didn't throw a single code, but would do this power-loss/bog-down thing about once or twice a week. when it was happening, boost would go to crap (like never exceed 2 psi), and ICP would top out at like ~2000 psi. with no codes thrown, I thought maybe it was leaking injector O-rings or a bad IPR. however, it also seemed like the IPR duty cycle was being capped at like 25%, whereas my other truck would easily get to 30-35% at wide open throttle. it was almost like the truck didn't know I was telling it to go fast. also, the engine was running and idling perfectly smooth, so it didn't seem like it would be bad fuel pressure or something mechanic causing the issues.

...so, I checked the Throttle Position Sensor on the go-pedal and found it slightly suspect. ...swapped in the pedal assembly from my other truck and it seemed to make a difference, then the problem came back.

then, I noticed that trans in the truck (auto) wasn't shifting according to the gear the scanguage was saying it should be in. I checked all the electrical connections on the trans and found quite a bit of fluid in the solenoid pack connector and that the connector wasn't quite seated right by the PO. cleaned it out real good and seated it right. the truck then ran great for about a week. ...then the problem came back. the, I started getting a P0107 code - which most online DTC lists show as "out of range low MAP signal" or something like that. I verified that the MAP line was clean, which it was (it was brand new along with the new MAP from the PO), and tried running with it unplugged - no improvement.

at this point, I was thinking maybe it was just leaky O-rings or low fuel pressure, but I still couldn't make sense of the low IPR Duty Cycle - maybe it was just the PCM itself...

so, I went ahead and did the e40d swap I was planning, hoping the PCM swap would fix things. while I had the PCM out, I checked the MAP sensor to PCM lines for continuity and short to ground. everything checked out OK.

...finish up the swap, take it for a drive and she runs great - for a day, then the problem comes back. so, I do some detailed interwebs searching on the recurring P0107 code and find that some places list it as: "low signal input MAP/BARO sensor" this was the first time I saw mention of the BARO sensor associated with this code. then, after some reading of the shop manual, I come across this line under the BARO heading in Electronic Control Systems: "0107 = Signal voltage was less than .04 volts for more than .2 seconds." Turns out it is a completely BARO-specific code. and it says this about engine impact: "The BARO signal if used to determine altitude to adjust timing and fuel quantity to optimize engine operation and control smoke throughout all altitude conditions." ...certainly worth pursuing.

so, I got out my wiring diagrams and checked all the wiring to the BARO as well as all location of Vref, thinking maybe Vref was low. interestingly, I found that the Vref line resistance to ground was ~700 ohms at the BARO sensor and ~500-600 ohms. I thought maybe this was my problem as the required spec in the manual is >1000 ohms (with engine off, key off). however, I checked the PCM pins themselves and they read 700 as well (not sure how the engine sensor locations would be lower than that, but oh well). so I then checked the other 2 PCMs of I have and they all read 700 ohms.

so figuring they're not all bad, I just swapped the BARO over from my parts truck and BOOM! she runs like a beast now and I've had no problems for a week+ . since then, I've noticed, that my IPR DC regularly goes up to ~30-35% and that I get much better low-end power that before even when I thought the issue was not happening.

so, it appears this BARO fault really was bogging down the engine electronically by limiting the IPR DC, or maybe ICP. and by doing that it completely kills boost, which coupled with the ambiguous DTC description had the PO and me thinking the MAP was bad all along, while it was really the BARO. also, with the new BARO, I've noticed my Injector Pulsewidth actually varies from 1.4 quite regularly and quite a lot. with the bad BARO sensor, it appeared to be pegged at 1.4 almost all the time (except maybe when coasting when it would sometimes, but not always go down to 0.4).

Moral - P0107 = BARO problems, and even without the code try a new BARO sensor with power-loss/bogging down issues on an otherwise smooth-running engine. not sure how much they cost, but probably not too expensive.

(and as usual, sorry for the book, but just wanted to get as much info out there for other's searching on a similar problem.

 

Wow, that's great info JP. I am going to recommend that this be added to the tech sticky for future reference. Mine has been doing something similar. I'll have to give this a shot.

 

Yeah, it really was like night and day after changing it out.

 

Can the Scangauge tell you BARO information, either voltage or calculated PSI? For some reason, my version of AE does NOT give me BARO.

 

no, it doesn't - but "boost" is the calculated value of the difference between and "Man Abs" (or whatever its called on the gauge) and BARO, so you can do the math (really fast) if you want. however, all the while that my BARO was bad (apparently), i wasn't getting any crazy boost numbers with the truck idling or off. in hindsight, though it may have read more negative at idle than it does now - like -0.5 - 1.0 consistently, whereas not its pretty much within a tenth of zero at idle.

the writeup on the BARO sensor in the manual does say that the PCM will use the MAP reading at idle for its "atmospheric" pressure reading if it detects a BARO fault. what it doesn't say is that it will also significantly de-fuel the engine as well!

from the manual explanation, the sensor is just a simple variable resistor that changes with pressure. i think it gives limit resistance values as well. i should check to see if its in range or just totally dead. ...and i should pull it apart to see if there is an obviously ruptured diaphragm or something in there...

 

Thanks for posting. Reps to ya

 

How long has your "fix" been working?

 

He said a week in his first paragraph.

 

Where under the dash is this? Who sells them?

Reps sent, good job JP!!

 

This information is amazing! Good God I feel like I have so much to learn about my truck, just when I feel like I have it somewhat figured out. So, here I am.....apparently I need to get a Scan gauge and a good electrical tester. My problem is not mechanical, but electrical. It gives me the heebie jeebies. Anytime a CEL went on in my truck related to the TPS/IVS stuff a few weeks ago, my knees would go weak. I just thought "how much is this going to cost and am I able to fix it myself?" JP, I may be asking you quite a bit here soon enough!

 

Actually it was in his 11th paragraph.


We will see if ANOTHER new one fixes the problem. I would bet there is something else wrong like wiring

 

well, this is a pretty terrible picture, but all I could find online: http://ww2.justanswer.com/uploads/wo...2_083213_1.jpg I think this is a top-view looking down through the dash. it is just above your knee though, pretty rearward (away from the firewall) under the dash though. it hangs pretty low too - you're knee's probably almost touching it while driving if you have long legs.

this is a picture of the actual sensor, though: Barometric Pressure Sensor Standard Motor Products As169. and looks like it costs $90 on that site I've never heard of. it has as 4-pin round connector going to it, but only uses 3 wires.

I am by no means an expert, but have learned a ton from everyone else on here, so i'm happy to give back or help point you to someone who knows more than I do.

when it comes to problems like this though, I am stubborn as heck and will keep plugging (and swearing) away until I figure it out though. not sure how I would have a snowball's chance in hell of figuring stuff out without the internet and forums like this, though.

Ha! yeah, I am pretty longwinded when it comes to posts. I always try to cut down on it, but also don't want to miss any info that may help someone along the way.


I did disconnect nearly every Vref signal location as well as the big-ole through-firewall connector and the PCM connector, for testing at the same time I replaced this sensor, so I suppose it could have been a bad connection somewhere that is now seated better, but considering the BARO-specific code I was getting, and the massive performance difference i saw after the swap, i'm pretty confident that was the issue.

if I find the problem comes back, i'll post that for sure. otherwise, i'll post again in another week if the problem has still not come back.

ALSO - if anyone else is doing PCM work or work on a sensor that uses Vref, i'd be curious of your resistance of Vref to ground (with key off). like I said, all three of my PCMs were in the 500-600 range, but my 97 shop manual says it should be 1000+ ohms. I get dead on 5V out of them with the key on, though, so that test passes, just not the Key Off resistance check...

 

I hope for your sake the BARO was the culprit. I had this type of problem on my white truck. I just decided to live with it since nothing seemed to fix it. Then an injector blew up. Once the new ones were in, the problem went away and never happened again. That was in May. I still don't understand why it was intermittent though.

If your problem comes back you may want to check your injector hold down bolts. Mine were loose and thats what caused the injector to fail. So my intermittent power loss problem was either directly or indirectly the result of loose hold down bolts.

 

Phil - how did yours run when the problem was present? did it idle OK? like I said, I was thinking of leaky injector O-rings or something mechanical, but it always ran so smooth, even when it had no power, that I'd have thought an injector problem or something would have some effect like a rough idle or rough running at high RPMs.

plus the intermittent-ness of the problem pointed to an electrical source for the issue - which I guess yours was as well, though driven by a mechanical problem...

anyway - time will tell, I guess.

 

It would run fine. I would smash the go pedal and it just didn't have any power. I don't have a boost gauge, but you could hear the lack of turbo whe nthis would happen. The next time you hit the pedal hard it would have lots of power. The problem drive me nuts for over a year. The idle on that truck has always been smooth but it goes up and down by about 50 rpm. It still does that. I have read that is normal for older engines. It has over 280,000 miles.