91 GMC K1500 Won't Start

[Brad_J]

5.7, 195K miles, auto 4x4 and has been overheated. Was idling rough when warm before breakdown. Gradually got worse with hesitating under load and occasional backfire before the no start.

Blue spark @ 3 plugs that I checked. Fuel pulsing from injectors and tried starting fluid with no luck. Engine just turns without catching. TPS voltages checked out but was throwing a code 22 before it died. I also moved the crank and observed less than 10deg of crank movement before the rotor moved. All plug wires checked w/ohmmeter and new plugs, cap/rotor, MSD Blaster coil.

My Chilton manual doesn't have much info as to which sensors are necessary for starting. Will a bad cam position sensor (or magnet) still let the ignition fire? I haven't seen where the knock sensor is located if that's messing w/timing.

Thanks for any help

[ronaldk]

You say you have good blue spark and 91 is probibly TBI so easy to introduce fuel, with spark and fuel and simple 1st gen ecm you should have some reaction so I figure wrong timing. put timing light on #1 wire aim light at marked crank turn over (it will still show if you indeed as you say have spark) see if its even close I would bet its not I could be wrong but I dont think so. If it is off it may be gear on distb (I believe it has dist) or timing chain. Good Luck

[Brad_J]

Thanks for the reply Ronald.

Some new info. I'm remodeling my basement so the truck's taken the back seat.

Timing is ~8deg BTDC while cranking. I'm assuming it should be ~0deg BTDC. Still no start. The distributor bushing has zero play in it. Is it possible the bushing stuck and caused the housing to rotate?

I also noticed that the coolant temp switch wire (near exhaust manifold) reads 50ohms between ground when disconnected. Not sure if that matters.

[2000CAYukon]

The coolant switch near the exhaust manifold is only for the gauge. The coolant temp sensor for the ECM is in the intake manifold near the tstat housing.

You could try unpluging the coolant temp sensor and try to start it. With it unpluged, the ECM will think the engine is cold and give it more fuel.

The pickup coil in the dist could be bad. Ignition module is another possibility.

Check that the vacuum hose the MAP sensor is good. My 90 will not start if the hose is disconnected.

//2000CAYukon

[Brad_J]

Is the 8deg BTDC abnormal at cranking? I could loosen the dist and bring timing closer to zero.

I'll double check the temp sensor and pickup coil tonight. I checked them when the driveability problems were present and they were within spec.

I wonder if the magnet that triggers the pickup coil is bad/damaged? I've been suspecting the distributor components but didn't want to start blindly replacing parts.

Will a bad pickup coil/magnet or ignition module still allow spark?

Thanks for the input.

[2000CAYukon]

8 deg BTDC is not abnormal at startup. Once the engine is running, it is usually at 20 deg BTDC. Is fuel spraying from the injectors when you try to start it?

//2000CAYukon

[ronaldk]

If you have good blue spark and fuel pumping in to tb like you say in op you even tried starter fluid. and now you verify timing is in spec I suspect improper air to fuel. A clogged cat that will not let eng breath will not allow fuel to ignite. When you have fuel,spark and proper timing you should have running eng if not unless you cooked all your valves or rings the only other thing is improper air to fuel. like map sensor but spraying ether it should have reacted. I can think of nothing more.good luck p/s if you confirm cat to be good do compression checkI do have one more thought, when you overheated eng you may have dropped a few liffers.I had a 305 van when I first started my busn a very long time ago any ways one push rod made a hole in rocker arm closing one valve on one cylinder and I could no longer drive it had no power maybe if more that one dropped it may not start. Long shot but if you take valve covers off someone can crank you can make sure all valves move.

[Brad_J]

I cut the exhaust just before the cat (rusted slip joint) and that didn't help.

Fuel is pulsing from the injectors while cranking.

I replaced the Distributor with a new Carquest unit and got it to stumble. It will run ~ 1000rpm if I hold half-throttle but will die as soon as I lift or depress the throttle. I rubbed my matchmarks off (sharpie and oil don't mix!) so will check timing later. The spark plugs were black and you can smell the fuel. Might pick up a new set to see if that helps. I'm sure the open exhaust isn't helping things!

I checked the coolant sensor again and it was within spec. one-wire o2 sensor shouldn't matter before reaching operating temp, right?

I don't have an adapter to read fuel pressure so that might be the next item to look at.

Thanks so much for your help.

[ronaldk]

I reread your op and I think I thought you changed spark plugs, but I see you checked spark plug wires. After overheat those plugs are most likely shot. you need to get your base timing. It probably explains in you new distr info.I still stand on the fact if you have air, fuel ,compression, and timed spark you have running eng, its just that the spark needs to happen inside cylinder. I am sorry I misread your first post. It really looks like it could be as simple as new spark plugs.I dont think you needed distributor but cant hurt.

[Brad_J]

Thanks Ron,

I had put new plugs in before the overheat but spaced out that they're probably shot now. The plug wires' resistance was fine but the factory wire guides are missing so I routed as best I could. I think I'll pull the valve covers just to see how things look and compression test a few of the rear cylinders before winter hits.

The previous owner had replaced almost every sensor without any luck in fixing the poor idle, so the distributor was next in line for me.

I'll see what happens tonight after the new plugs and I need to reconnect exhaust before my neighbors get riled up.

[ronaldk]

As long as you are changing plugs make sure all you wires are good.Also keep away from exhaust. My sons 95 camaro was really shaking cause he got two wires to close to exhaust ( of course dad fixed).Now thats a hard veh to change plugs and wires.Ya anyway let me know how you do. I will check your post as much as I can. I know you will get it running cause once theres direction theres hope.I would have someone turn over when you remove each plug even if you can't put gage on for compression you would still have idea that valves are closing by the air being pushed out on each cyl, just a thought?! Good luck One more thought you say it was running poor when warm( Was it ok cold cause its in open loop cold?)before overheat. Check for vac leaks, your thottle body gaskets may have fallen apart. And try pulling vac line on egr and plug so egr stays closed (although it may be leaking at pinicle) if you pull egr to check buy egr gasket when you reinstall you need new one each time.

[Brad_J]

SUCCESS!

I moved the dist one gear tooth because the module wires were holding me back. Installed new plugs and she fired up and idled. I checked timing at idle and it was running well at 2deg BTDC. If I moved it to 0 deg, the engine started to stumble. Prior to warm up, the timing was between 14 and 20deg BTDC.

I ended up replacing the battery and starter after I killed both of them (they were on their way out anyway). And now it starts like a champ.

I have to tweak the timing a little I think because it stumbled a little moving around the driveway. The gas is ~5months old so I'm sure that's not helping.

I checked compression with the weak starter/battery on 4 cylinders and had 125-140psi dry. I haven't checked the compression with the new starter.

Thanks to everyone who replied. I couldn't have done this without your input/help.

[Brad_J]

So I jumped the gun. I had it running for about ten minutes the first night and it ran great. Good throttle response but was a little shakey when in gear driving around the yard. This first start was with the nose pointed approx 20deg downhill.

I parked it on a sidehill and have not been able to get it started again except twice idling for approx 1 minute.

I put in a new fuel filter and TBI rebuilt kit (gaskets, o-rings). I have a little over half tank of 5 month old gas but I thought I put Stabil in it.

I'm going to try to rig up something to read fuel pressure. Besides the gas quality or a worn fuel system, I'm at a loss.

[ronaldk]

Ok I reread your first post. You have a chilton book, if its same as mine #8055 then read pg 2-6 eng disturbed, how to time is a matter of aligning rotor with notch on distributor base. Once that is done correctly the ecm will take over. If you do this and your timing continues to change erratically then I would suspect problem in wires or ecm. 5 month old fuel not great but I have several classic cars and have had older with only small effect on power cars always start.Its still a good idea to check your fuel pressure. Good luck let us know how you do.

[Brad_J]

I had it running for a day after draining ~8gal fuel and replacing w/5 fresh gal. I warmed it up, shut off, disco'd timing wire, started and timed to 0deg, shut off, and reconnected timing wire. Drove it for ~ 1/2 hr and no major issues. Still died a few times idling, but nothing like before.

Went out the next day and it coughs and sputters if I hold 1/2 throttle but won't stay running. I'll have the wife crank while I check the timing again.

I didn't look for the notch in dist so I'll re-time using that process. The plugs were black from it running poorly so I cleaned the electrodes as best I could. I have to buy a different fuel gage that has the GM TBI adapter to get fuel pressure.

Thanks for the help Ron. I've never been so frustrated with a vehicle but there's only a few other things it could be.