Hello trouble shooters. I have an issue with my van that is driving me nuts. 96 was the transition year from OBDI to OBDII and my van was early on the line so it did not get the OBDII system. I am getting what I describe as a stumble when trying to accelerate in the higher gears. The transmission shop says it's not the tranny, it is not slipping, and are telling me it's an engine problem. The only code I am getting is a 172 HO2S lean. When this stumble happens I can also hear a knock in the engine like the timing is off.The timing was off because of a loose distributor, but I reset it. That did not clear the issue. Because it's OBDI the scan data is limited. One thing I am noticing is the Loop is going Open intermittently as I drive.
I would appreciate it if someone with the talent to interpret the data below could to tell me if there is anything so far out of whack that it might provide a clue about what might be causing my acceleration stumble.
Any direction is appreciated
Thanks

Also, I should mention that this van has no MAF, only a frequency based MAP / BARO.

Codes Report:
DTCs (Codes)
111 ECM
Sys Pass Code No Faults Detected During
KOEO Test

KOEO

------------------------------
111 ECM
Sys Pass Code No Faults Detected During
KOEO Test
MEMORY

==============================

DTCs (Codes)
172 ECM
HO2S System Lean Bank 1
KOER

Here is a frame where the van is in Closed Loop:
CANST PURGE On
ECT(V) 0.7
ECT(°F) 185
ENGINE SPD 1012
EVP(V) 0.2
EVR(%) 0
FUELPW1(mS) 2.0
IAC(%) 4
IAT(V) 1.3
IAT(°F) 142
LOOP STATUS Clsd
O2SEN 1(V) 0.75
SPARK(°) 12
ST FTRM1(%) 10
TOT(V) 1.3
TOT(°F) 145
TP MODE C/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 41

Here is a snapshot where it jumps to Open Loop:

CANST PURGE On
ECT(V) 0.7
ECT(°F) 185
ENGINE SPD 1016
EVP(V) 0.2
EVR(%) 0
FUELPW1(mS) 2.1
IAC(%) 4
IAT(V) 1.3
IAT(°F) 143
LOOP STATUS Open
O2SEN 1(V) 0.75
SPARK(°) 11
ST FTRM1(%) 10
TOT(V) 1.3
TOT(°F) 145
TP MODE C/T
TPS(V) 1.2
VPWR(V) 14.1
VREF(V) 5.0
VSS(MPH) 41

Here is another snapshot at a higher RPM, but I am not sure what was happening because it looks like I am accelerating pretty hard but VSS speed is zero. I do not recall racing my engine while standing still:

CANST PURGE On
ECT(V) 0.7
ECT(°F) 180
ENGINE SPD 2636
EVP(V) 0.2
EVR(%) 0
FUELPW1(mS) 2.5
IAC(%) 62
IAT(V) 0.9
IAT(°F) 167
LOOP STATUS Open
O2SEN 1(V) 0.00
SPARK(°) 35
ST FTRM1(%) 10
TOT(V) 1.1
TOT(°F) 157
TP MODE P/T
TPS(V) 1.5
VPWR(V) 13.9
VREF(V) 5.0
VSS(MPH) 0

Steps I have take that should be mentioned:
Round of Injector Cleaner
New fuel filter
Throttle body cleaner
Checked motion of EGR valve, it responds to vacuum testing
Check MAP / BARO (As this is a frequency output device and could not do spec test because I do not have a scope, but vac holds and supply voltage is good. Borrowed a new one from NAPA and it did not change issue so I assume MAP is OK)
Found distributor loose, pulled SPOUT and set base timing 10 degrees BTDC
Checked cleaned PCV valve

 

Hi,
I drive a '94, e350 .,5.8l club wagon .
I few weeks ago I was experiencing something similar.
I would recommend you to check your TPS. Your readings do not look right. At 2636. RPM your voltage should be higher than 1.5volts. TPS controls fuel injection, transmission shifts and other engine tasks. When this happened to me, I had no acceleration and I thought it was the transmission too but it was the TPS. A lean code also mean lack of fuel. Check your fuel pressure just to make sure it is where it should be.

I would go after fuel pressure first since it is easy to check with gauge. If that checks OK , go after the TPS. At any case, if you replace the TPS, use a Motorcraft one.

Good luck.

 

Thanks, that sounds like good advice. At the moment I am looking to see if I have any vacuum leaks. I found what I believe is a small leak in the vac to the A/C Heat control. When I pump it down it does go up but slowly, I don't think that is supposed to do that.I may just cap that off temporarily. If it will stop raining long enough I'll check the vac on the AIR B/D and the EGR sol. In the process of doing that I'll move the bracket blocking access to the fuel pressure test port and check that out.
I also have a question I have been trying to get answered. Could it be the PCM is messing up and misreading the engine RPM's? The VSS sensor in the rear axle sends the signal to the vehicle PCM which then translates that to vehicle speed, but where does the PCM get the engine RPM's? I don't think there is any engine speed sensor because I can't find one or any mention of one in the shop manuals. The only reason I suspect this is because of the high 2636 RPM's in that last frame while showing 0 MPH. I treat this van with kid gloves and I would never rev the engine like that which looks like a WOT. Got me scratching my head.

 

hi,
With regard to your question: Can the PCM be messing up ?
I guess anything is possible. Specially due to the fact that your van(my van,for that matter) is 20 plus years old. If you live in place where snows , corrosion gets into connections creating all kind of trouble. The only issue I have experienced with the PCM in my van was the leaky capacitor.

Pertaining to the VSS, a faulty VSS can also cause all kind of drivabilty issues. My personal experience with the VSS happened a few years ago during the winter months. My transmission did not want to shift and the check engine light would come on. When I replaced the VSS with Motorcraft one , my issue was solved.

How the the PCM gets the RPMs? From the distributor(crankshaft,hall affect,magnetic field). The VSS,TPS,RPMs signal and other sensors send the info. to the PCM and then the PCM interprets the inputs and tells engine and transmission what to do.

Good luck!.

 

I doubt it's the VSS because I am not seeing any issues with my speedometer or cruise control, both of which rely on that signal. Other reasons I suspect the PCM is that even though I have a set 170 code, my Check Engine Light is not on. The bulb is OK cause it comes on for the self test when I start the van, but otherwise it never comes on. Plus, the PCM was replaced about 6 years ago and I just discovered they didn't even use the correct model. I looked it up and this PCM was designed for a 97 F series pickup truck. It's a miracle it's worked at all for the last five and a half years.

 

No that isn't a miracle, your truck is SD and that system was used on many HD trucks up until the end of '97. The last scan you posted looks like the vehicle was stationary, 2600rpm is just a minor goose of the gas so no that isn't accelerating hard and everything else looks OK.
The lean code on back 1 could be a bunch of things, and exhaust leak, a leak in the air injection system, a leak in the EGR system, or a dirty injector. Have you looked at the plugs lately? If one of the plugs on the passenger side(bank 1) is white while the others are brown tan that injector is dirty, if they are all white you have a global lean problem which suggests a leak somewhere.

 

UPDATE:
Just wanted to say thanks for the suggestion and other input. After running down the list of items to check I got to the point of checking the cylinder compression. They all came in around 178 psi., which I guess is OK. While I was at it I replaced the plugs and wires. I immediately noticed the poor condition of the wires when one of the boots crumbled as I tried to remove it. After a test drive and much to my surprise, my issue had disappeared. The old plugs didn't look bad, but apparently the wires were bad enough to cause the stumble I had been experiencing.