1972 k10 6.0 swap need help on road trip ...

[suburban99]

As title says I am driving my recently swapped 6.0 k10 from Vancouver to kelowna...going up snowshed hill my check engine light came on for a second then off...truck seems to defuel...done this several times now...but will do 75 on the flat...
Have Bosch handheld on board:
No codes
Temp at 196
Iat is 57
Running closed loop

Fuel pump connections and filters checked on side of road..there good
Any help ideas...MAP? Altitude about 4000 ft

[Jstock85]

Maybe the density of the air has an effect on the fuel air mix at 4000 ft above sea level. just a thought

[suburban99]

I have no VSS hooked up yet...could this be the issue ?

[68c10airstream]

What fuel injected system are you running?? Some aftermarket systems don't have altitude compensation charts built in. Mass air flow, or speed density system? What brand??

[suburban99]

Stock LQ4 fuel injection with return line to tank. Walbro in line fuel pump stock tank. Using the stock return connection as 72's had one...check engine light flashes when it bucks, but I don't know if the engine is trying to stall or if it is getting defueled somehow..still no codes

[dayj1]

Originally Posted by suburban99

going up snowshed hill my check engine light came on for a second then off

Originally Posted by suburban99

check engine light flashes when it bucks

Originally Posted by suburban99

I have no VSS hooked up yet

A flashing check engine light indicates that the engine is currently misfiring. The flashing will stop when the misfiring stops.

Based on the lack of VSS and the fact that it is happening while climbing a hill, I'd speculate that your torque converter is locking early or at a time when it shouldn't and loading the engine too much.

If you had a bad coil or other cylinder specific problem, you'd likely have a check engine light that stayed on and a code indicating an error on a particular cylinder.

Get your VSS hooked up or your PCM programmed to work around the lack of it and you'll likely be good to go.

[suburban99]

As I am running a TH350 tranny without a VSS output, what are my options?
Also don't have a lock up converter...thanks much for your help!

[suburban99]

What if I unplug the CTS to keep it in open loop? Seems to run ok when cold...Just gotta make it back to the coast on Friday..:

[dayj1]

Originally Posted by suburban99

As I am running a TH350 tranny without a VSS output, what are my options?
Also don't have a lock up converter...

Well, then, it's not TC lockup

If the check engine light is flashing, then it is definitely misfiring. And the part about climbing hills make sense as it's under the heaviest load at that time. I recently helped track down a similar issue with a fried's LS swap and it cleared right up when he replaced the plugs and wires. If yours weren't replaced when you did the swap, that's a good place to start. Otherwise look for fuel or ignition related problems that would cause a misfire.

[Hart_Rod]

Does it sound like you are getting any Knock? Can you log your spark advance or Knock retard? Sounds like something is causing the computer to pull some timing...

[suburban99]

Well made it home after a 400 mile round trip thru the mountains.
Here's more info:
Up small grade it will flash the check engine light and stumble...continually until I backed off to 1500 rpm then would stop.

-Plugs and wires are new
-Check engine light flashes when under load and engine stumbles.
-When first started I can get up to 4000rpm +...when it stumbles(under load) it will barely run at 2100rpm...
-Fuel filters are clean
-I removed plugs and cleaned them and reinstalled before the return trip.

Runs fine in neutral ...idles good, starts good.
PCM was reflashed by a member here and was flashed to a 4l60E or 4l80E (can't remember) but it's written on side...I am running a TH350

I read on another site that the crankshaft sensor can cause a misfire and not set a code.

Has no codes..

Thanks for the help so far!

[suburban99]

FWIW even with the misfiring i still averaged 17MPG thru the mountains...same trip with the 350 was 12 mpg...same tranny..waiting on Dakota Digital VSS setup now. Hopefully that cures it.

[Daaaanz67]

Subbed

[68c10airstream]

I'm a little curious about something. No codes and many, many misfires with check engine flashing has me thinking about you may be loosing the 12 volt "+". On another post there was mention of a fuse box issue where there is poor connection. If this was the case it would misfire and have no memory of the event because the battery supply cut out. Worth a check, good luck!

[suburban99]

Originally Posted by 68c10airstream

I'm a little curious about something. No codes and many, many misfires with check engine flashing has me thinking about you may be loosing the 12 volt "+". On another post there was mention of a fuse box issue where there is poor connection. If this was the case it would misfire and have no memory of the event because the battery supply cut out. Worth a check, good luck!

Yea I checked the wiring and relocated the PCM fuse to outside the fuse block to make sure it had good +12...same misfires after...

[suburban99]

Ok installed the Dakota Digital speed sensor parts and no more misfire!
Engine idles down better at a stoplight as well. Highly recommended...

[BR3W CITY]

VSS becomes more important on newer stuff too, since the 4l80e's, newer 60's and most of the other newer trans' run both an ISS and VSS (sometimes one labeled as an OSS) and will compare things like output shaft speed to other sensors (wheel speed). Some setups can't run at all without one or larger changes to a series of tables.

You also have stuff like DFCO, the DOD/AFM stuff etc that uses speed sensor data to make decisions in terms of function.