I recently did an engine swap 350 for 350 from an 1986 to a 1986 but the new engine was on propane new carb and elec. fuel pump well it ran fine for a while and about a week later it just stalls if you dont constantly give it fuel so i shut it off and it wouldnt start so after a few new spark plugs i got it to start but it just pukes black smoke and throttle lacks response and if left to idle it stalls any ideas?

SOURCE: 1999 Yukon cold start problems.

1999 Yukon Start Issue - I have replaced the octopuse, battery, fuel filter, fuel pump, still having problems starting in cold weather, sometimes after a heavy rain.

Any suggestions?

Thanks

Marvin

• 85242 Answers
• Posted on May 22, 2009

SOURCE: 98 GMC k2500 7.4L Rouch Idle

TRY THIS BEFORE U SPEND ANYMORE MONEY N PARTS.
Here is the common cause of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

SOURCE: 93 gmc sierra 5.7 liter engine, injection carb,

you say you replaced the fuse, but does the fuse have power? the gray wire at pump should have power when cranking, or for 2 seconds when turning key on. At fuel pump relay, put power onto gray wire, the pump should run if the wiring is good. if it doenst run then ck for power at fuse while power is on gray wire.

SOURCE: I have a 1999 gmc yukon 5.7 litre v8 4wd with

check the mass air flow,and the tps sensor

Harvey N Tawatao

• 3854 Answers
• Posted on Mar 16, 2010

SOURCE: 95 GMC Sierra 4x4 350 5.7 rough idle problem

It sounds like a MAP sensor going bad. MAP is short for manifold absolute pressure sensor, it senses the manifold pressure and applies the right amount of gas with the right amount of ignition timing so the car runs and performs well if this does not work properly. It throws off the whole loop cycle for the computer, which in turn makes it run badly and get poor fuel economy. It can causes the engine to have a lack of power, combined with a loss of fuel economy. Poor take offs and sometimes an occasional stalling may occur if the MAP sensor is faulty and sending the wrong signals to the ECM.
Hope this helps and thank you for using Fixya.
Here is a link that my help you in the future. http://www.troublecodes.net/GM/