Hi guys, I'm new to the forum and need some help with a bit of a head scratcher.
This is gonna be a long one so apologies for all the reading!
I have a 2001 chevy blazer with a 4.3l vortec. It's an automatic with around 75-76k miles
A couple of weeks ago the eml came on, I plugged it in and it gave a p0341 camshaft position sensor performance. It was also running quite rough intermittently.
I checked the wiring to the cam sensor with a multimeter and all was OK. So I ordered a new cam sensor and fitted it and cleared the code.
Went to start her up and the truck wouldn't start.
Removed the cap and rotor to ensure everything was done correctly and it was as both components only fit 1 way. Refitted the old cam sensor still nothing. Checked to make sure everything was plugged in that I had disturbed and again all ok.
Checked all plug wires were in the right place and again all ok.
So I began testing; first tried to start the truck with carb cleaner down the intake - nothing. Checked spark from coil, nice blue spark jumped 1 inch gap.
Checked wiring to ignition coil with multimeter and again all ok
Checked spark with spark testers on plugs, all light up indicating spark was getting to the plugs .
Removed spark plugs and found all plugs wet and slightly blackened (plugs were replaced approx a month ago). All plugs dried in a few seconds.
Checked all plugs for nice blue spark again all ok.
Refitted plugs after cleaning but still no start.
Checked fuel pressure from shrader valve on top of intake - 55 psi when ignition position 2.
60 psi when cranking. Left it all connected for 10minutes pressure dropped to 55 and held.
Took a sample of fuel as car was recently filled. Fuel ignited instantly when exposed to a naked flame and burnt clean.
Poured 1/4 of a beer can of new neat petrol into the throttle body - still no start
Did a compression test;( I don't have exact cylinder numbers on me right now but can get them when im home) cylinders 1,2,4,5,6 all had compression in the range of 160-175psi whereas cylinder 3 was only 120psi so seems to be a loss of compression however the truck surely should still run on 5 cylinders so I don't think that's the issue here although will likely need addressing at some point. This test was done dry so I will check cyl 3 again with some oil incase it's been washed with fuel.
Checked the timing rotating the engine by hand to the 2nd mark on the crank pulley and the rotor arm lines up with the no. 6 mark on the distributor.
At this point the truck had killed the battery from all the cranking so I had to use a battery from a different car which again the truck did not start.
I've tried running earth's from the battery to the engine using jumper leads to rule out an earthing issue and again still no start.
I've tried multiple batteries with jump packs on and still no start.
I removed all the starter motor connections and cleaned them - still no start
I've checked all the actual values in the pcm and transmission and all appear to be ok, there is also no issues with communicating with the car or the pcm.
After all this I went back to ignition as I have a running 99 blazer and a bunch of parts from a donor blazer.
I swapped the cap and rotor from the donor and still nothing.
I've also checked the resistance of both caps and rotors and all points are below 1 ohm.
From what I've now researched both the cam and crank sensor shouldn't prevent the vehicle starting so I think I can rule that out.
Only other thing I can think Is the truck does have a lower intake manifold leak which is very common on this engine. That said It was running and should still run even if it has got worse.
I have removed the distributor cap and cranked the engine and the rotor arm turns clockwise smoothly without stopping at any point which should rule out a worn distributor gear though I haven't pulled the distributor to check yet.
I've checked all the fuses and swapped the fuel pump relay to no avail
There are currently no fault codes in the vehicle.
I've also tried moving plug wires forward 1 place and back 1 place and again nothing.
New fuel filter was fitted approx 2-3 months ago.
Also no security light when cranking and actual values show signal to start is given so I believe that rules out the crappy pass lock 2 system.

As you can see it's passed every test (apart from cylinder 3 compression) so far and I'm at a bit of a loss for where to go next so any help would be much appreciated!
I'm hoping it's just something silly that I've missed.

 

Anyone got any ideas?

 

1. Did it start OK before you replaced the cam sensor?
2. To confirm, it wont start with the old sensor either now?
3. How strong is the spark at the plugs? Check that coil to distr lead
4. Is it possible that the distr moved while doing all of this? Is it the original hold down with limited movement or do you have a wide adjustment set up?
5. Did you do anything else that can effect the timing?

George

 

Hi George,
1, It was starting before the repair was carried out but it was sat for a few days while I was waiting for the part to arrive and I didn't start it before replacing the sensor.
2, correct it will not start with either the old or the new sensor fitted.
3, it is a strong blue spark at all
of the plugs. There is also strong blue spark from the end of the lead attached to the coil.
4, Possibly but unlikely as I didn't remove or unbolt the distributor at all though I did have to turn the engine over by hand to remove the cam sensor so if the gear was worn maybe it slipped. That said the distributor rotor lines up with the no.6 mark on the distributor when the 2nd mark on the crank pulley is lined up with the line on the block. I have also never touched or adjusted the distributor on this truck and there is not side to side play, it is held down firm and in place with the factory clamp.
5, nothing that I am aware of like I say all I've removed is the cap, rotor and spark plugs. I've disconnected a few sensors and the brake booster hose from the servo but that was all reconnected prior to attempting to start. The only other thing I've done is turn the engine by hand.

 

1. Does it catch erratically and or backfire while cranking or is there zero combustion?
2. On these older trucks the rubber damping ring can slip on the flywheel so that alignment can be ubnreliable
3. If you are grounding the plugs to the block to check for spark then the block grounds are probably OK but if not then check those
4. Is the oil in good shape (no water or gas)?
5. If you know for sure that you have good compression, cylinder ignition and the gas in the tank is not bad and it will not fire up with starter fluid or good gas down the hatch then there are not many potential causes:
   1. Timing problem. Sounds like you did not disturb the distr but maybe the timing chain or distr gear jumped. There should be some crappy cylinder ignition however. The gold std for getting to TDC is measuring through the spark plug hole.
   2. The plugs are severely fouled with carbon or water (LIM gaskets). Sounds like they are wet but evaporate quickly so I assume that they smell like gas. Try cranking with the accelerator floored to force flood clear mode

George

 

1, it usually just cranks and cranks and cranks though it has backfired up the inlet twice over the 4 days I spent testing it. Which would signal a timing issue which is why I checked the timing originally.
Both back fires occurred at the end of a period of cranking. One of the backfires occurred after several attempts of cranking and the other after I poured the neat petrol into the throttle body. I'm pretty sure what came out the intake was fuel as opposed to combustion gases.
2, I did read a post about that crank issue but I've yet to pull it off to check, I wanted to go down as many other avenues as possible with the hope of rectifying the problem before removing components which could potentially lead to other issues but it is something worth checking.
3, yes I tested spark by grounding to the block and also ran a lead from neg battery terminal to the block so I think the earth's are all ok.
4, oil is clean and has been changed recently in the last few months, no evidence of any coolant into the engine even though the intake gasket is leaking.
5.1 ill check the timing again by lining everything up and checking for tdc through spark plug no.1s bore and let you know the results.
5.2, the plugs while slightly fouled shouldn't be bad enough to prevent proper ignition as they have been recently replace and I have since cleaned them and refitted with no luck. They did smell like gas and as you say dried quickly which again should point back to ignition.
I have tried full throttle position while starting which did not work and I've also tried with the vehicle in neutral.

I think the best step forward is as you say to properly verify timing so I'll do that and report back.