Join Date: Feb 2017
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Good Truck gone Bad?!? Substantial Drivability Issues
Bear with me while I get all this out of me head and written down so maybe someone here can steer me in the right direction.
Built 5/97 Cali Truck CCSB 4x4 (As far as I have been able to tell it was bought and kept in Utah till I bought it in 2012)
PCM - MME0 (Pretty sure this is what I saw when I had the kick panel off)
Cal - 7-90P (That's the sticker in the door, pretty sure it's never been updated)
PO installed Guages, ATS Intercooler, 4" exhaust, Superchip programmer. Everything else appeared stock. It seems the PO used the Truck to pull a 5er for vacations only as it took 15yrs to rack up 88,000 miles (I know about the 5er from the rails in the bed and google earth images of his house =).
I brought it to Texas and starting driving it cause it just makes me smile. Near 120k the torque converter started to fail and wasted the front pump. I rebuilt and upgraded everything necessary inside according to BTS (I wanted him to build it but I didn't have time for the back log) and put a PI Converter in front with the lower stall option. 40k later zero troubles there so I must have done something right for a change. I did have BTS tune the valve body when I was passing through a year later and those guys are truly helpful, I wish I had had more time to hang out.
When the trans was out, I replaced the up-pipes & doughnuts and found a missing gasket on the turbo output that helped the truck make a bit more boost.
Slight regression, the problem I've been trying to solve since I bought the truck is that the truck will go extra sluggish on occasion for me, never enough to get too excited about but I've chased the problem on and off to no avail b/c I've not found anyone else on here or the other common sites with similar enough issues that were ever solved and I’ve never found sensor data that was way out of line using my AE diag scanner. I've always thought that boost was a bit low but everyone I talked to chalked it up to the intercooler doing its job. It's never performed like other powerstrokes I've driven or ridden in but it’s been manageable and like I said it makes me smile to drive it around. I've never been able to get boost over ~18psi on the gauge in the truck but I've never really had a trailer on it that weighs more than 6-8k. I've always run the Max Performance program until yesterday when I put it back to stock to make a record of drive-ability in stock now that my problem has become so much worse.
The problem history goes something like this; other than the less than stellar performance on occasion, it also 2-3 times a year would throw P1393 and or P1391 Glow Plug Low Input. Usually this would happen when it's cold (texas cold, like maybe freezing) but it’s happened several times in the middle of summer too, always at a cold start for the day. I never thought too much of it b/c I never had trouble getting the truck to kick off and I knew that when I bought it, the dealer had just replaced 3 of the GPs and it usually went away after a few key cycles. I did visibly check the harness connections outside the valve covers and re-seated the connectors. I've not seen any evidence of overheating of the plugs or harnesses but I'm not ruling that out, I just haven't explored it further.
This year I decided that since it was giving the code more frequently I would go ahead and replace all 8 GPs and gaskets and under cover harnesses. Hasn't been done yet but all the parts are on the bench.
Then the other day (2/10) a fuel puddle shows up under the truck. I check it out (2/14) and find a leak from the fuel pump or accumulator saucer under the turbo mount so I've got parts on the way for that. While I'm poking around I decided to dig out my computer and do a little more investigating with AE since I'm going to have the valve covers off soon maybe I'll find something helpful and at least be able to log a few miles before and after to see if there are any noticeable differences. So, I've got my laptop hooked up and I run some of the diag tests, notably I run the buzz test twice. First time I didn't really know what to expect, second time it sounds pretty much the same. All definitely buzzed and from where I was standing there was slight pitch change from inj to inj but none seemed to exhibit a major difference (However this is the first time I've run this on my truck and other than the general idea of what it is supposed to do I can't claim expert knowledge) I'm not sure if the buzz test is supposed to return any values but it said that it passed.
Real Problems start when I fire the truck up after the buzz test. Now it sounds more aggressive at idle like a 49 state truck, and a bit lopey. Then I try to drive it and it can barely move. RPMs don't want to go over 1500 with the pedal on the floor at first and LOTs of whitish/bluish smoke. I finally make it down the street a bit and RPMs start to pick up and power is better but it’s still very low on power. Further down the street, I can get the truck up to 40mph and it seems to smooth out a bit but when it goes back to idle, definitely sounds like it’s missing a cylinder or two. I should note that the truck had been driven earlier in the day so it wasn’t stone cold but it wasn’t warm either. As it warms up, power gets better but timing is different for sure as the truck sounds more aggressive throughout the range, and shifts are more abrupt. Eventually the truck seems to run almost stronger than it used to but there is still a noticeable miss or lope at idle and it’s slow out of the gate but otherwise drives normal or slightly quicker.
Back home, I hook up AE and run a cylinder contribution test and it sounds at several points like it might not make it through. Really rough some times and tons of smoke (smoke may be normal for this test?) Only codes were P1393 and P1391. I went to drive it again and record some data and it drove almost better than normal above 1200 rpm but there and below it was grumpy.
Truck kicked off fine at first this morning but after it idled for a few minutes it was getting progressively weaker and rougher sounding. Again, it barely made it down the street with almost zero power and more smoke. Once it was out on the road and I opened it up a bit, it drove like before, rough idle and low speed but seemingly as much or more top end than I’m used to. Smoke stopped after getting out on the main road. When I came back home I plugged AE in again and went for another data log drive. It felt about the same as previous night. I had a friend suggest swapping back to the factory programming to see if that recalibrated anything, so I did. Other than losing more power and resetting how the trans shifts it didn’t seem to make much difference. I did make a data run in the stock configuration while warm for records. Then I put my fans on it for a few hours to try to make it cold again to see how it would act so I could record that as well. After 4-5 hrs, the oil in the pan was at ambient and so was the valley so it was as cold as I could get it. Started AE and cranked up the truck to make a record. Took it for a drive to get it warm and performance was unchanged.
In reviewing the data I can only find a few anomalies that don’t really point to anything I understand about how these trucks are supposed to function. The biggest weird thing I found is that the Engine Coolant Temp Sensor seems to act bananas but the gauge acts fine and it’s my understanding that this value isn’t used in control so I don’t know if I should let this distract me or not. Engine Oil Temp seems to be acting normal. Injector Control Pressure stays around 500 at idle and goes up to 2500 or more when accelerating. Map sensor seems to be showing appropriate changes in pressure with accel. Throttle position is slightly goofy, I cannot get it to go over ~75% squished to the floor. I have floor mats but I haven’t pulled them out, maybe they are interfering but only at the top end. Vreff stays at 5.01.
Any ideas to go from here that don’t immediately involve pulling injectors? I’d be grateful for any suggestions as what to look for next. Again the only codes it will throw are P1391 and P1393. I did run the CCT again and it acted about the same as before and only posted P1391 and P1393. I guess really I need to solve those first with my new plugs, harnesses, and gaskets and see if that’s the magic bullet but if anyone has some special insight, I’d love to hear it.
I attached the AE Datalogs if someone feels inclined to poke around and look for all the obvious stuff I missed.
Last edited by aggiediesel01; 02-15-2017 at 11:07 PM.
Reason: found a typo