i have had my ls1 swap for 5 + years now and never let me down till saturday.I wanted to move it outside to finish wetsanding it and it wouldnt start just crank and try every now and then and when releasing key it would kickback and backfire out sidepipes.First then checked fuel pressure,had 60 but when id release it nothing came out but air after cycling key half dozen times i would get fuel but not alot.So tuesday i put a new walbro inline pump with new filter/regulator in,it now has fuel but still no start,acts like it wants to but wont.Pulled plugs all 8 fuel fouled,dripping.Cleaned them reinstalled first try almost started but didnt,after that just extended cranking and fouls plugs right back out.Pulled wires and checked for spark all 8 coils have great spark.Also the tach is moving all over while cranking so its telling me crank sensor is ok,PLUS SPARK AND FUEL TOO..So pulled fuel rail to check for stuck injectors all 8 spray fine and no drips.Last night i did a compression check in 3 cylinders so far and 2 had 195,but cylinder 1 had 90,ok now worried,was able to get alittle oil in it not much a few drips,tough with modified sidepipes and it went to 135.Ok so either i got ring problem ring land broke or fuel washed that one cylinder down.Im gone to test other ones tonight if i can get in there.I pulled intake off before work and pulled cam sensor to take to work to see about ohm test,but cant find what the reading is supposed to be if anyone knows that would be great.Thing i dont get when i parked car 2 weeks ago it ran fine no miss no codes,always fires up first try.Even after cam swap in may it started right up.even if i lost cylinder 1 it would still start just miss,im almost at a loss.Was gone to try new cam sensor and fresh plugs and see if i can get it to start.What else?

 

Sounds like it started with a fuel issue, any chance a lean backfire damaged the timing chain/gear?
Check the rockers while cranking.
Any codes?

 

No codes at all,it has backfired pretty hard last few nights,ill pull covers tonight and check rockers.thanks

UPDATE finished compression check 190-195 in all cylinders but number 1 which i got some oil in again and i got 125 tops.also i realized thels1s have a 3 wire cam sensor so i cant check ohms anyway ,with 7 good ones and one low it should still run,just doesnt make sense it rn great 2 weeks ago and then barely start to no start to low compression in 1 cylinder.Valve covers off everything looks good opening and closing no broken springs which are brand new.

 

Hello Pat, long time no read. Of course #1 cylinder is the problem. It is an LS1 isn't it?
Well anyways that #1 cylinder is dead but ya know, most sb chevy will still run pretty good on just 7 working pistons. I think now as a minimum to pull that head. But for the sake of it u could pull the rocker arms on #1 and see it it starts with both vlvs shut. What did that plug look like?

cardo0

 

Hey whats going on,all plugs look exactly the same black and fuel soaked.Im gone to pull the motor out but i want to find out whats not letting it start first.Over the winter ill find out what went wrong in number 1.Thing thats got me mad is i only have 585 miles on it since i built it heads have only 2500 miles on them.But i have been thinking all this time i never ran the steam vent its always been blocked off,just since i swapped cam and convertor a few months ago i hooked it up.Maybe its been damaged and finally the fuel wash down there lost any seal it had left.Ill find that out later just need to figure out what wasnt letting it start.Im gone to throw in new plugs cam sensor and give it one more try then next week ill pull it out.

 

btw, did you post over at LS1tech? There is a lot of experience with problems on the conversions forum.
You might also want to check sensor readings for those that could be damaged by a backfire. MAP, MAF, check intake manifold vacuum, etc.

 

Blown fuel pressure regulator is my guess.

 

Well i put a used cam sensor that we knew was good and new plugs and fired right up.Ill let it run tommorrow for awhile and check compression in number 1 again after hot and see what it is.Ill be pulling it out anyway to see whats up with it but its running again.

 

Sounds like its rejecting the inplant!!!

 

I'm intrigued, I would love to hear what you come up with. So you think the cam sensor was the problem at this point, and not allowing the ECU to send spark to the cylinders? Was the sensor replaced when you rebuilt the motor or is it the original from the factory?
Were the plugs wet with fuel only or did you find coolant on them? The steam lines, if blocked off, will create a hot spots in the heads where the air is trapped, I'm not sure that the steam lines would give you gasket failure unless your heads have warped do to excessive heat from the trapped air from the blocked steam lines.



Riggs

 

At this point im not too sure on anything lol,the cam sensor was used when i did the swap so it couldve been bad,its just weird no codes thrown for cam sensor at all but thts the only other thing i changed.I let it run today for over an hour,i did notice it was extremely rich today need to put my efilive back on,log a idleing file and see what its doing something not right.As far as cylinder number 1 after it ran that entire time compression was 125,so its coming back out this week before i start painting.

 

Hey Pat, glad to see you got it up and runnning again. Maybe an A/F sensor since its running rich?