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2003 S10 4.3L Cranks but won't start


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This adventure began as a intake manifold gasket replacement due to a water leak at the intake gasket at 205k.  One week prior we had replaced spark plugs and wires, thermostat, cleaned MAP sensor with MAF sensor spray, and cleaned the throttle body with throttle body cleaner while it was still bolted in place on the plenum.  Engine started and ran better than it did in the prior 8 years of care free ownership.  

The following week the water leak went from a drip to a free flowing leak, so I replaced the gasket, and reinstalled everything over the period of one week.  We reinstalled the distributor by aligning both marks on the harmonic balancer, and the rotor pointing to the #6 on the distributor, #1 cylinder on compression stroke TDC.  Great compression.  Tough to spin the crank with a standard 1/2" ratchet. 

A week after the tear down we were ready to start the engine for the first time.  We had to crank it a lot, but eventually the engine started, ran rough for 30 seconds to a minute or more, them magically smoothed out and idled perfectly in an instant of time.  I let the engine come up to temperature gradually at idle, allowing gaskets to seal up, add coolant, check other fluids, then went for a drive after it had been up to operating temperature for several minutes.  Having had access to clean the bottom of the throttle body while it was removed made for a perfect idle after reassembly, and great throttle tip-in response.  It was flawless.  Drove it out in the countryside for about 20 to 30 minutes at 55 to 60 mph.  Just before I got back to the house the oil pressure gauge was sitting at zero.  A light clicking/ticking sound started after about 20 seconds idling in the driveway in disbelief.  Freaked me out. 

Changed the oil.  Topped of coolant again.  The next day I tried to start it, but no start.  Since then I have rebuilt the starter.  It spins well now, but struggles to crank beyond a few seconds, like the engine is out of time, but I don't know that it is.  I replaced the distributor to take care of the common camshaft position sensor, cap and rotor failure points.  I have changed the fuel filter.  We dropped the fuel tank and replaced the fuel pump (pressure was in the mid 40 psi range while cranking), but the new pump now supplies 62 psi while cranking.  Every time we pull #1 plug to find TDC on compression stroke to reconfirm mechanical timing, the plug reeks of unburned fuel, and the plug is black.  We have confirmed mechanical timing at the crankshaft and distributor rotor 5 separate times.  There is fire at the coil, at the head of the distributor cap where plug wires connect, and at 2 of the 6 spark plugs using a spark tester tool.  As I crank the engine, trying to start it, the oil pressure gauge gradually rises to about 20 psi on the factory gauge. That's a relief. 

The engine really tries to start if it has sat for a few days without being cranked (working on it while I have time).  

One pair of old mechanics suggested that it may be flooded, to pull all 6 plugs and let the fuel evaporate.  

Another guy, a engineer covering the racing circuit suggested dropping the distributor back in with one gear tooth counterclockwise of the "correct' location to retard the timing, and make starting easier.  

I am open to suggestions, and testing recommendations.  I may have forgotten other steps I've taken, but I have exhausted 3 old mechanics, 4 if I count myself.  Mind you we are old school, and do not work in a shop for a living, but we aren't complete idiots either, LOL.  

Thanks in advance for your help.


Since my last post, I have re-verified that the engine is still mechanically in time. Both crankshaft marks aligned, and the distributor installed with the rotor pointing at the inner ring timing indicator mark, on the compression stroke, TDC.

I have removed the fuel pump relay to prevent additional fuel pouring into the engine while we cranked the engine to verify compression stroke on cylinder number 1 Top Dead Center. The rest of the fine aligning was done with a wrench on the crank pulley.

As an experiment, we also have dropped the distributor in with a one gear tooth retarding of the timing, which probably corresponds to about 15°, and tried to start the engine. Yes the oil pump shaft was connected correctly, and with the fuel pump relay re-installed the engine still did not start. What are your recommendations? What are your questions? Thank you

4 Answers

You said you installed the distributor rotor pointed at #6 with the engine balancer set at TDC on #1.  Why didn't you point the distributor rotor at #1???  If you have the motor set at TDC for #1 cylinder, the distributor rotor has to be pointing at the #1 position on the distributor.

Thanks for your reply. You've asked why didn't I point the distributor rotor at #1? Fair question. I may not have worded my explanation clearly. I was in a hurry. If you are a GM service tech, I do not mean to lecture, but every authoritative process guide and YouTube video on this topic has been unanimous that the reassembly process requires me to drop the distributor in with the slot that drives the oil pump aligned, and the rotor pointed where the machined dimple on the drive gear aligns with a faint white line that is imprinted on the distributor shaft. Maintaining this alignment as you drop the distributor in results in the rotor spinning in a clockwise direction. When the oil pump connections are properly seated, the rotor is be pointed to a small triangular alignment mark on the interior of the distributor ring. The alignment mark has a #6 molded into it. I followed their instructions, all of which were completely foreign to me, and I still cannot start the engine. Now, if you are a GM service tech, what I am learning from you is that everything I have read and viewed has been incorrect. Please follow up with me. Thanks


I would definitely plug in the fuse for the fuel injection and give it a squirt of starting fluid as well.  Then, let'er rip.  For future reference, whenever I take out a distributor from the old days, I use a paint pen to put witness marks on it to be able to reposition it properly.  Same for vacuum lines and wiring.

Yes sir. I thought I edited my reply, and then pressed the "save" button, but apparently I did not. One of my corrections was to say, "We did not un-plug the fuse on the fuel injection circuit . . . " I realize that by not removing the fuse, it could have the effect of continuing to pour fuel into the cylinders.

Got it. Thanks.

Saw the 2nd half of your message just today, 'Doc,' and making a witness mark on the distributor is the one thing I rushed past on the initial tear down. That said, I felt confident that I could reassemble correctly because I did know exactly where the rotor was pointing before I pulled the distributor. The rotor was pointing directly at the middle spark plug wire (head) on the right side of the distributor cap. The paint pen is the ideal tool, and I didn't have one available. I was concerned that the rotor seemed to drop back in during reassembly just a few degrees clockwise from where it came out, and we did not rotate the engine during the intake gasket replacement, or following the rest of the job. That slightly different alignment was, and still is concerning. I don't know how that rotating was even possible. We did mark vacuum lines with tape.


The firing order for your engine is 1-6-5-4-3-2.  If the engine is set at #1 TDC, the rotor must be pointed at #1 plug wire on the distributor, other wise, you will be 60 degrees off (360 degrees rotation divided by 6 cylinders.) if it is pointing to the number 6 cylinder spark plug wire.  Each TDC for each cylinder is 60 degrees apart.  Yes, the distributor has to fit in the slot to function, but it must be turned so the rotor is pointing as closely as possible to the number one cylinder position on the distributor for the spark to be correctly timed to the compression stroke.  It is very common to put the cap wires in the wrong place on the distributor cap.  I would make sure the engine was set at TDC for number 1 cylinder, install the number one spark plug wire in the position the rotor is pointing at and follow around clockwise to attach the other spark plug wires at 6-5-4-3-2.  FYI - I am fairly certain of the above firing order but you need to confirm that for your engine as I saw some say the firing order is 1-5-3-6-2-4. 

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Yes sir.  I agree with everything you have explained, and I also recognized the one character mistake I made while typing my description, both times.  On the inner ring of the the distributor is a triangle-shaped pointer (timing mark) that has stamped into it the characters v6 (not #6).  From your description I can conclude that this timing mark (v6) corresponds to spark plug #1.  Yes, I have flipped the cap over to follow the tracings across the cap, and have recognized that they lead from the opposite side of the cap to the #1 spark plug lead.  Yes, we have retraced the plug wires from cap to plug at least twice, and in fact on our first retracing of the wires we noticed a mistake at the cap, two crossed wires on the right side (about 2 weeks ago), then corrected them.  I agree with your firing order, 1-6-5-4-3-2.  That firing order was also confirmed at a NAPA store.  Now, having corrected my typing error, acknowledged that I noticed a pair of crossed wires (at least 2 weeks ago, perhaps 3) at corrected the mistake, and that the engine still will not start, I welcome your next thoughts.  Some have suggested that the engine is flooded.  The last time we cranked the engine it did try to fire very early in the first cranking.  Eventually we decided that I should depress the gas pedal to the floor and hold it there for 2 to 3 successive crankings.  If the engine was flooded, that step failed to get it to start.  We did not plug the fuse on fuel injection, and perhaps we should have, I don't know.  Time to work on it has been very short for the past 2 weeks.