Weird no start after oil change.
 

i have a 1994 k1500 5.7 standard transmission. Truck ahd been running fine and ran fine sunday morning. I drove it to buy the oil and filter (5w30 high mileage and pf454). Then after the oil change it wont start. It'll crank for days but wont fire. I wasn't getting spark so, long story short, i got a new cap and rotor and new plugs and am now getting good spark (i checked the firing order 3 times). Fuel is fine too. i just bought the oil pressure sending unit and am going to replace that tomorrow i guess. Can anybody think of what else it might be? Tanks in advance!

Re: Weird no start after oil change.
 

Are there any check engine lights on? If so what are the codes. Usually if you have spark, and adequate fuel pressure (minimum 9psi on TBI 350) it's a timing issue. Is it spinning really easy like it's not making much compression?
Pour a little fuel down the TBI unit and see if it tries to spit to life. That would indicate a fuel problem. If not, pull the cap and see if the distributor is rotating like it should when cranking. If so, throw a compression tester on #1 and see what the numbers are. If way low suspect timing chain. The spark kernel should be a whitish blue/purple. Orange is weak spark.

The ignition module in those older sencond gen HEI unit can do some weird things.

Dan

Re: Weird no start after oil change.
 

My first thought with your post was the oil pressure sensor. Some have 2 oil pressure sensing units, some combine into one. IF it gets disconnected or possible broken, it will not allow the engine to start as it says there is no oil pressure. I believe the "kill" one is a sensor down near the oil filter.

Re: Weird no start after oil change.
 

I changed the oil pressure switch under the distributor cap last night and no change as far as the starting goes. After shutting off the ignition i could still hear the fuel pump on so i disconnected the battery to make it stop. Im kind of at a loss now. Ill look for the the other oil pressure switch today after work.

Re: Weird no start after oil change.
 

A 1994 K1500 only has one oil sender. If bad it will not prevent the engine from running as long as the fuel pump relay is working as it should.

It is normal for the fuel pump to run for 2 to 20 seconds after the key is turned off.

A bad oil sender can cause the fuel pump to keep running.

If the contacts in the fuel pump relay are melted together it can cause the fuel pump to keep running. If you find that is the problem the fuel pump current flow is most likely excessive and the fuel pump needs to be replaced.

Did you remove or turn the distributor?

Re: Weird no start after oil change.
 

Ok, fuel pump still running gadter ignition shut off. We know that not normal. Pull up a wiring diagram of the ignition switch and get out the ole volt-meter. Based on that bit of info I think I'd be looking at the ignition switch as a possible culprit or at least a place to start.
Still, if as you said you have fire (spark at the plugs) and fuel it should start barring a mechanical timing issue...

Dan

Re: Weird no start after oil change.
 

I did get it to run for about 10 seconds with the gas pedal to the floor. As soon as i lifted my foot it died. I went ahead and ordered a fuel pump. this thing is driving me nuts.

Re: Weird no start after oil change.
 

This sounds like it was flooded. If you poured fuel down the TBI that could cause this.

A bad coolant temp sensor that the computer monitors can cause to much fuel to be injected. The computer monitors the coolant temp sensor by the thermostat housing. It is a separate sensor then the one for the dash gauge. You could have bumped the wire to the coolant sensor when you were doing the work on it. You should check the connection.

There is also a ground in the front area of the intake usually close to the thermostat the is very important. That ground is where the computer and computers sensors get their ground.

You may want to try unplugging the injectors and cranking the engine to get the fuel cleared out of the engine. It may start when doing this if there is still excessive fuel in the engine. Then reconnect the injectors and see if it starts. If an engine gets very flooded the spark plugs my need to be removed and dried / cleaned.

Re: Weird no start after oil change.
 

The other night I unplugged the injectors and tried cranking and nothing changed. i also took out all the plugs while the injectors were unplugged and cranked it in hopes of drying it out. no change. Ill check on the possibility of loose wires tonight.

Re: Weird no start after oil change.
 

Is the spark a blue color spark or a orange color?

Strong spark will be blue in color. Orange color spark comes from weak spark.

Re: Weird no start after oil change.
 

Nice and bright blue/white spark.

Re: Weird no start after oil change.
 

To clarify: I advised pouring a little fuel in the TBI to see if it starts. By little I mean a couple 2 or 3 ounces. If you pour a couple pints in it and most that makes it into 1 or 2 cylinders that a condition called hydo-locking and it will do severe damage. Line broken piston, bent rod, sometimes both.
At this point with what's been described so far I would be thinking about the fuel pressure regulator having failed. If you pull the fuel pump relay located on the passenger firewall and then pour a couple ounce down it with no more than 30-40% throttle and it fires just fine then that's a strong indication of the flooding condition ChevyTech described. If you ha e to hang it wide open to fire and it still runs rough it likely being flooded to death.
Is the check engine light on? If you or a friend have a scanner oull any codes. Since you TBI unit lacks a Schrader valve it's not as easy to put a fuel pressure tester on. You usually need an adapter the goes between the TBI and the pressure/feed line. This is why I suggested the earlier method.
Hope you get it figure out without too many head aches or money.

Dan

Re: Weird no start after oil change.
 

SOLVED!!

I was on vacation and started a new job so i had not worked on the truck for a few weeks. So after some wild guessing and a shot in the dark we replaced the ignition coil and it fired right up. Very strange. Lessons were learned, money was spent, beers were drank, 4 letter words were mumbled (and shouted) Thanks for all the suggestions guys. I really appreciate it :metal:

Re: Weird no start after oil change.
 

Strange indeed, since you said you had good spark?

Re: Weird no start after oil change.
 

You’re telling me! I can only assume the spark wasn’t strong enough or consistent since it works now.

Re: Weird no start after oil change.
 

I worked in electronics for ~thirty years. What you think is a good connection and looks like a good connection might not be a good connection. The first thing to do in unplug and plug the connections a couple of times to clean any corrosive build-up. When that gets too bad you replace parts. Glad you got it solved.