I've completed an engine swap on my 2000 Chevy Silverado 1500 with a 5.3 Vortec engine. Is there a recalibration procedure that is required? It is only starting intermittently. No codes are showing. When it fails to start, it's turning over and coughing, trying really hard to start, but never lighting off. When it does start, it fires right up with the twist of the ignition key.

What I did:

Reman direct replacement long block from VEGE / Summit
Reman starter
New flex plate
New harmonic balancer
New front accessories (water pump, power steering pump and pulley, belt tensioner, belt idler pulley and alternator which was upgraded to 145 amp from 105 amp)
New AC compressor, lines, accumulator, and condenser
New Mishimoto larger capacity radiator, with oil cooler and larger aux transmission cooler
New oil cooler lines
New sensors (crankshaft position, camshaft position, throttle position, idle air control valve, oil level, oil pressure, engine coolant temp and three AC pressure switches)

 

Are the new sensors GM or Delco brand? Not saying that IS the issue, but there is the possibility.

 

G Atsma -

Thanks for replying. I should have mentioned that in my original post. All sensors are from GM with the exception of one of the AC pressure switches, which I had to get from Dorman.

 

Fuel pump or fuel filter issues? Have you checked the fuel pressure at the fuel rail?

 

Sauceman, will it stay running with some throttle? If you’ve got oil pressure, try some throttle. You won’t hurt it. You shouldn’t need any tuning work for it to run, unless the new engines camshaft, or other parameters are different.

 

Thanks TJ. I did not check fuel pressure. Will do tomorrow.

 

Che70velle -

When it starts up, it runs great. Will stay running at idle and responds to the throttle. I had it up to 3500 RPM, and it was as smooth as silk. Oil pressure is good.

This engine is listed as a direct factory replacement, which, I unfortunately need in California.

 

Attached.

 

Attached.

 

Attached

 

Cam sensor related.

THIMK about the cam & crank pos sensors. Remember, each cyl comes to TDC TWICE during one engine cycle, which a cycle takes 2 complete engine rotations: once it's the TDC instance when it fires, and the other is when its exh valve is just closing and the int is just opening. The cyls come to TDC in pairs, and the pairs are those that are 4 cyls apart in the firing order: 1 & 6, 8 & 5, 7 & 4, 3 & 2. As each pair comes to TDC, one of them is firing, and the other is at that other point. The crank sensor tells the ECM where the crank is at all times, down to the resolution of the reluctor tooth count; this is how it knows when it's time to fire one or the other of each pair. The cam sensor tells it where the cam is, i.e. which one of the pair is the one that's at its firing instance of TDC. It only needs this one time for each run cycle, namely, right when it's trying to start up, since once that's established, all it needs to know for it to keep running, is the crank pos sensor, and all it has to do is keep repeating through the firing order after the right starting point has been established. The crank sensor can tell the ECM which pair of cyls is at TDC when that occurs, butt if the cam sensor isn't working right, it won't know which one of the pair is at firing and which is not; and it'll act EXACTLY like the old SBC or BBC or any other distributor-controlled engine would, if the distributor was installed "180° out". It won't be able to run, butt there'll be spark anyway, just, at the COMPLETE wrong time; namely, when the valves are "changing over". Fuel in the intake and/or exhaust will light off, and spit back through the throttles and/or pop in the exhaust. With a stock cam and its short duration, the int valve doesn't begin to open until somewhat after the spark occurs, therefore it'll only and always pop in the exhaust. The ECM in our engines is evidently smart enough to know that if the driver tried to start the engine butt it didn't start, and if it isn't getting cam pulses, then the reason it didn't start might be because it guessed wrong which cyl of each pair it should have been firing; and the next time the starter is engaged without turning the ignition off and clearing its "memory", it'll try the other cyl in each pair, and see if that makes it run. The end result is, EXACTLY HALF the time, it'll start up perfectly; the other EXACTLY HALF, it'll pop in the exhaust; and if it does the 2nd thing, then turning the key back from Start to Run and then back to Start again, will make it fire RIGHT UP like nothing was ever the least bit wrong, and it'll keep right on running happily until the next time it's turned off and tries to start up again. I have no clue why this condition doesn't set a CMPS code, butt w/e, it doesn't.

I'd suggest swapping the old cam pos sensor back in and see if that fixes it. It's not impossible that the cam itself is the problem butt I wouldn't think that that's all that likely either.

 

Agree with RB04av. If your cam sensor is done, which I doubt, they huff and puff for 10-15 seconds before starting. It will eventually start. Try to check the harness/pigtail from the sensor for any damage. It will help if you have a DVOM, and know how to use it.....

 

Thanks for all the great input so far.

Is there a scanner that will read the cam position sensor? I have an ML629 MaxiLink by Autel with the ability to read live data from a limited number of sensors the CMP is not one of them.

The cam position sensor makes the most sense, based on RBO4Av's description. The engine behavior is close to what he describes, but the successful start rate is maybe 10% even if I go from start to run back to start versus start to off to start.

 

make sure all of your pins/plugs etc. in the harness are tight and making full contact when plugged in

looked at a cts-v locally here awhile back that was having the same issue and it ended up being one of the pins in the crank sensor had pushed out of the back of the connector and wasnt really making contact