Two guys were here yesterday picking up some parts, and one of them has an OBS PSD ('97 manual trans I think) that has a sluggish running issue. He said it will do it hot or cold, doesn't matter, but it's intermittent. He said sometimes he gets in the truck, starts it up and takes off, but the truck has no power, and the turbo won't spool up. He said if he switches the ignition off, then immediately right back on, it straightens up and runs fine. Other than telling me that the CPS was new, that's all the info I got. What could it be causing this, that switching the key off and back on would clear up? Anybody have any ideas?

 

Could be the ebpv closing and the shutting it off resets it.

 

I think I've got the same thing going on in my truck. Its hard to judge though because I don't really have a baseline. I know it likes to be warmed up a bit before it likes to be driven.

 

That's my thought Gabe. Worth checking out.

 

He did also tell me that the ebpv was unhooked, I forgot about that.

 

I unhooked mine also. I wonder if they get forced shut. I reckon I should take a reading of backpressure and see what happens.

 

Generally, if the EBPV is working and connected then what he describes is normal, on a cold morning. Of course after the EOT get up to about 135*, then restarting, it should never cycle on start-up. Also when restarting if the oil temp is above ~32 then the valve will cycle once for the PCM to see it's working (via back pressure sensor) then not activate during the rest of driving cycle. Ambient air temp also is a factor so sometimes the ~32* point is not valid. If it see's really cold then for whatever reason it has an override on EOT. I've actually seen this on one of those cold freeze foggy mornings. Monitoring the exhaust back pressure certainly would tell the story one way or the other.

I've monitored these sensors during cold mornings and here is what happens. On those morning I always know if it is going to activate while driving. The reason I say this is because I cannot hear, on initial start-up, the EBPV cycling. My best guess here is the PCM understands the valve is functioning due to the last cycle drive and does not want to activate it for performance reasons (cold start). Once underway the valve will cycle depending on load demand and can be quite concerning if one does not understand the logic the PCM is attempting to do. After driving a few miles if I shut the rig down then restart and, since the oil temp is above 32* then all this nonsense stops. However if I continue to drive the valve will still operate attempting to rapid warm the engine until the EOT has reached 175*. At that point the EBPV ceases operation and remains open.

When the valve is functioning properly it's quite desiring due to the fact one is trolling down the highway but with zero boost. Guess the PCM fuels differently when this occurs to keep moving, don't know .. but it seems to work. To see this happening you need to monitor EBP (exhaust back pressure), EOT (engine oil temp), AIT (ambient air temp) and exhaust temp. And yes, it does help in rapid engine warmup a bit as the exhaust temps will go up 100* to 200*, but where I live it's no big deal.