I just rebuilt the engine in my 2000 sonoma and when i tried to start it up it just spins NO COMPRESSION!?!?! Apparently the valves arent closing all of the way. We triple checked the timing before we reinstalled the engine. So other than any possible suggestions as to what the problem could be, I need to know if there is any way to udjust the valves on this particular engine because it has roller rockers. I would appreciate any input you may be able to provide. Thanks
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Process of elimination of possible faults. A code read might provide a short-cut but otherwise bear in mind an engine needs fuel, spark, timing and compression to start and run and with modern cars the immobiliser must also be considered when one or more of those things are absent.
That popping - backfiring sound would indicate the spark is not in time with the cylinders. Why is another question. The distributor cap could be cracked or defective, the timing chain could have failed, or something going on with the ignition module among other things. A mechanic would run a compression test or otherwise make sure the timing chain is ok before proceeding.
By 'just spinning over', do you mean there's no compression? Have you done a compression check? If you have no compression, then your basic crank/cam timing cannot be correct, or your valves are not closing.
If your ignition timing is 180 degrees out, you'll have normal compression, but since the spark is coming at the wrong time, the engine will not run. You'd have to remove the distributor and reinsert it with the rotor at 180 degrees from where you took it out.
Take it back to the shop that did the engine overhaul. No compression at all? They did something very wrong. Does the distributor shaft and rotor turn when cranking the engine? Are you sure your compression tester is working and hasn't failed? Is it possible they got the timing for the crank and camshaft all wrong? Take it back to them and demand they fix it, if it truly has no compression. It will never start without compression.
You'll lneed to test for 3 things:
Spark at the plug
Fuel, making it to the cyliinder
Compression, above the minimum spec.
Sometimes when engines have been rebuilt, they have really poor compression as they try to start for a few minutes of cranking. If you have good oil pressure, check compression, if low add a tablespoon of oil to each cylinder to build compression, as soon as it starts it will begin to seat and seal itself, as well as provide ample lubrication.
For Fuel and Spark, just normal diagnostics, based upon your description, I won't mention doublechecking now that it has been cranked a bit.
WD40 can be sprayed into the intake while cranking to get one lubed a bit and to start to idle, it will stall when you stop spraying, indicating a shortage of fuel.
You need to make sure you have fuel, spark and compression.
Remove one of the plug wires, stick a screwdriver (or other suitable item into the end of the wire. Then hold the exposed metal of the screwdriver about 1/2 and inch from some metal (engine block, intake manifold, etc). Be sure to keep clear of the fan/belts and wear gloves (as you could be shocked). Have a helper crank the engine and watch to see a spark between the screwdriver and the metal on the engine.
Check the fuel pressure to make sure you are getting fuel.
Check the compression with a gauge.
By completing these test you will know which route you need to look into.
MOST TIME A REBUILT IS HARD TO START.YOU HAVE PRIME THEM SQUIRT OIL IN ENGINE REMOVE THE SPARK PLUGS TO BUILD UP COMPRESSION.AND PRIME THE CARBURETER OR TBI ..BUT IF YOU ARE GETTING FUEL AND SPARK.PROBLEM IS YOUR TIMING IS OFF.
are these adj rockers? if so then take the nut down till you have about 1/4 in bolt sticking above it, then see if it will start, if it does then back each rocker off till it starts clicking then tighten till it stops clicking then go another1/4 turn thats your running adjustment!!!
a common problem with the jaguar aj26 v8 engine around that year is low compression due to wear on the nicosil coated bores to get it started you can try removing the fuel pump relay in the boot/trunk fuse box and cranking the engine and keeping the throttle pedal to the floor when it fires get someone to help and put the relay back in has it fires.if not take all the plugs out and put a couple of sqirts of engine oil from a oil can or similar in to each cylinder crank the engine over a little with plugs out refit the plugs and retry