rough idle, stalling, sweeping vacuum

[bobboz]

Hey whats up guys, working on a 95 k1500. I bought the truck with a frozen engine but it came with a motor out of an 89 suburban (engine sat a couple years). Ive been using the forum finding answers to common questions but i cant find it. I changed everything over to the suburban motor and swapped it in. First time starting it i just had the exhaust manifolds on and it ran rough and loped alot, and had fire in the manifolds ( not really backfire fire but engine off and a flame in the manifold. Figured i was getting too much gas with the new pump and dried up tbi so i cleaned and rebuilt it and put the exhaust together so the o2 sensor could get a reading from it, also changed the ignition module with another one i had. forgot to say once it ran for a little bit and shut it off I couldnt get it to start back up until it sat a long time. I started plugging every vac port I could and finally i was just down to the map sensor, When i disconnect the sensor it would start and idle without stalling, i checked for vac leaks and didnt come across one with carb cleaner. I went to check the vac pressure and the gauge fluctuates so much that i really cant get a good reading its almost like full gauge sweeps. it will run but has a miss or two and when the idle goes low I hear a ping/detonation/knock (not sure how to describe it except I have heard it on motors that are "dieseling when turned off). going from the vac reading and diagnostics i have found online most are saying valve problems and some are saying egr problems. Has anyone had something like this and it be caused by the egr? Also while cleaning the throttle body i did not mess with the iac or tps, after cleaning it I dont smell the gas like i did and the spray looks lighter so im hoping that fixed my over fuelling problem. any

 

[bobboz]

Looked up some part numbers and the knock sensor i had in there was the wrong one changed that lil improvement. Checked egr, it didnt hold vacuum, had a spare that held and sealed so i swapped that. not really improvement that i could tell. I reset the comp codes and hooked everything back up. able to start it if i give it some throttle and it will idle, I actually drove it down the road and back. the clanking i thought was pinging actually has nothing to do with the internals(turned out oriellys gave me too long of a belt and the tensioner is almost at full rest clanking from vibration) so now i have a hard start, rough idle, and miss fire. Codes i got were 34- MAP sensor circuit malfunction, 42- ICM EST IC bypass circuit malfunction (I forgot to plug the orange wire in before i started the truck so im guessing it threw this code) 54 - Fuel Pump circuit low voltage (not sure why this threw a code, Pump tank and oil sender are all new)

 

[skylark]

Something tells me that a compression check will be horrible. Your valves are sticking.

 

[superj]

full sweep on the vacuum gage means head gasket or cracked head, right?

 

[bobboz]

Honestly I'm not sure. Googling it I've really only found it indicating valves (said small sweeps not full sweeps) next day off I'm going to do compression and hook an air hose to check valves. Was hoping to change the distributor in it this afternoon with an extra I have ( when changing the cap and rotor I noticed it had more play than the spare I have) and on carbed motors I've had this solve misfire but I never checked their vacuums before. Kinda new to vacuum tests

 

[bobboz]

well got off late and the whole time at work i kept trying to think what else it can be besides something internal (didnt want to rebuild it or anything as im trying to keep this a cheap truck) but curiosity got the best of me and figured id check the drivers side compression before i hopped in the shower. Sure enough cylinder 5 had zero pressure the others showed 150-155. Took the valve cover off and the spring was down and there was no play in the pushrod so i gave the rod side a couple taps then cranked it and nothing. gave it a couple more taps and it freed up. cranked on it and it worked like it should. put the cover back on and fired it up and it runs great, well runs smooth but when i got down the road i remembered i didnt connect the alt back up and from all the cranking i barely showed 9.5 - 10 volts and it died once i got in the driveway and would only fire up then immediatley die. let it sit for 5 minutes and it cranked back up and ran fine. Thanks for the help guys, i guess a valve stuck fully open will cause the vacuum to jump like that havent checked it now but im sure its a hell of alot better.