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98 5.0L Vortec won't stay running

This is a discussion on 98 5.0L Vortec won't stay running within the Technical / Maintenance forums, part of the General Discussion category; 98 K1500 5.0L Vortec 4x4 Auto. 193K miles. I bought this truck not running. Water in the oil, would turn ...

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    98 5.0L Vortec won't stay running


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    98 K1500 5.0L Vortec 4x4 Auto. 193K miles.

    I bought this truck not running. Water in the oil, would turn over, but not start. Not sure if the intake manifold is bad or the head gasket(s).

    After some diagnosing, found that it had a bad fuel pump, that would only carry about 40 PSI. New fuel pump installed. I now have about 68 PSI key on, not running. Holds about 58 PSI while cranking, sputtering/running. PSI taken with fuel pressure gauge on fuel rail.

    Truck has spark and will actually run for about a second, maybe two, but runs REALLY BAD, sputtering, before it stalls out.

    Previous owner said it ran fine before it "just quit." I want to hear the truck run to decide whether it needs a new motor or just a new intake manifold gasket or head gaskets.

    Any ideas? Any guess as to whether it's the intake or head gasket?

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    Re: 98 5.0L Vortec won't stay running

    Compression test will tell you if it is an intake gasket in most cases. You could put a radiator tester on it and build pressure (no more than 14-16 lbs though) and see if you can see/hear any leaks. With water in the oil, the bearings may be torched anyway, so a rebuild might not be a bad idea in the long run. If you do, put a 5.7 in it. I don't know what all is involved, but it shouldn't be much, if anything. It will be the same price to rebuild (you will have a little for a good core, but you can probably sell the 305... even if only for scrap. The 5.7 is soooooooo much better of an engine. At any rate, I wonder if you have issues with cam/crank position sensor phasing (maybe the guy that had it started to take it apart and then just decided to sell it so he just stuffed things back together. The other thing I would look at is the cap and rotor. These trucks have issues with caps and rotors. Mine is very finnicky about the brand that I use and I chased issues with severe corrosion until I discovered that the vents in the underside of the distributor were plugged. I cleaned them out and all has been well since. One word of warning, the distributor body on these trucks is a composite material (think: plastic). The cap hold-down bolts are torx headed (T-15 or -20 as I recall). Be carefule when you put them back in to make sure they aren't cross-threaded and you don't over-tighten them. I always use the old screws since the new ones come with some kind of hard thread-locker on them that has a tendancy to put enough stress on the threads to bust the threads out of the housing. Ask me how I know... Good luck and let us know more as you work through it and we will try to help you out.

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    Re: 98 5.0L Vortec won't stay running

    Thanks jkesselr.

    The only code I get with my scanner is P0336 - Crankshaft Position Sensor A Circuit Range/Performance. I have no idea what that even means. I know you mentioned the crankshaft/camshaft sensors phasing. Is there something I should be testing?

    The engine doesn't appear to make any bad noises while it's cranking so I'm unsure of the condition of the bearings. That's a big part of why I would like to hear it run, if only for a minute or two. Then I can decide on a new engine or not.

    I haven't messed with the distributor cap or rotor for the sole reason as it did sputter and run for a second or two. Now it just seems to want to crank and not even sputter.

    I appreciate the help, if you have any more ideas let me know. I'm getting frustrated with this.

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    Re: 98 5.0L Vortec won't stay running

    Which type of cap and rotor should I get? Any other suggestions to try?

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    Re: 98 5.0L Vortec won't stay running

    The crankshaft position sensor is located just behind the harmonic balancer. Its held in place with 1 bolt, and it has a weather pack type connector on it. There is a wheel with 4 arms on it, as these arms move pastthe cranshaft position sensor, teh PCM sees 1 pulse. Everytime the cranshaft turns 1 full revolution, the PCm sees 4 pulses. this is a 4x reluctor wheel. Sounds like you are having issues with this system.

    The truck wont start/run without a crankshaft position sensor signal.

    the code P0336 - Crankshaft Position Sensor A Circuit Range/Performance is telling you that you are having an issue with this system, either the sensor itself or its wiring.

    be sure to check all the underhood fuses as well.

    peace
    Pauly
    97 GMC 2wd RCSB 5.7, s10 2700 footstall, Hooker 24621hkr LT's , 2.5" cats dual 4"pipes exit B4 pass. side tire, custom driveshaft 3.42 G80 FIPK MAF descreen GM/Mercruiser Marine intake manifold 29lb LS2(EV6) injectors Ed Wright PCM(best mod), LT4 KM 14.8@94mph 2.007 4000lbs 122mph

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    Re: 98 5.0L Vortec won't stay running

    OK, I'm getting fuel in the cylinders because the spark plugs are wet with gas. I have a spark at each cylinder, but it is only orange. I'm under the impression that the spark should be blue.

    Is my ignition coil bad, or just the cap and rotor?

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    Re: 98 5.0L Vortec won't stay running

    Could be either, but if you have fuel and spark to each cylinder, you need to check to make sure that the thing is timed correctly. This is going to rely on a few things, crank position sensor, cam position sensor (and their phasing to one another - this is what sets the "timing" on these motors). Given the code you received, I would start there. If your crank position sensor is shot or not functioning correctly due to malfunction or wiring issues, it isn't going to run right no matter how much fuel and spark you have.

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    Re: 98 5.0L Vortec won't stay running

    Is there a way to test the crankshaft position sensor to determine if it is reading correctly?

    I was sure with fuel and spark that it should run, and was completely overlooking timing.

    Is an orange spark hot enough to burn the fuel in the cylinders? I would think that if I had ignition in the cylinders, the cylinders would be dry.

    Keep going with ideas, I appreciate everyones help.

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    Re: 98 5.0L Vortec won't stay running

    if the CKP sensor was bad, you shouldnt get any spark.

    peace
    PAuly
    97 GMC 2wd RCSB 5.7, s10 2700 footstall, Hooker 24621hkr LT's , 2.5" cats dual 4"pipes exit B4 pass. side tire, custom driveshaft 3.42 G80 FIPK MAF descreen GM/Mercruiser Marine intake manifold 29lb LS2(EV6) injectors Ed Wright PCM(best mod), LT4 KM 14.8@94mph 2.007 4000lbs 122mph

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    Re: 98 5.0L Vortec won't stay running

    Yeah Pauly, that's what I've learned from my research: A bad cranshaft position sensor will yield no spark.

    I'm getting an orange colored spark at all the plugs. Could it be a bad or weak coil?

    I took the crankshaft position sensor out to clean it and make sure there was no obvious deficiencies. I also checked the voltage and cranked the engine with the sensor out. Do I have to recalibrate the CKP sensor now?

    It's slow going, but you guys are helping me figure this out.

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    Re: 98 5.0L Vortec won't stay running

    If you haven't replaced the cap and rotor yet, I would do that first. While you're back there, check the camshaft position sensor plug and make sure it makes a good connection. My truck ran like crap- surging, bogging out, and misfiring when mine had an issue. As for what kind of cap to buy, the caps with brass terminals seem superior to the ones with aluminum terminals. OEM is always my first choice for parts.

    Have you had the ignition module tested yet? Just to narrow things down. Could be a weak coil also. What about the plug wires? You never know what you inherit when you buy a used truck. You can check the resistance on them. I think I would do a full tune up first, and then see what happens.

    Are you sure that the CKP sensor code was CURRENT and not a HISTORY code? Because the other guys are right in that you won't have any spark without the pulse from the CKP. That signals the ignition module to fire, then coil, etc, etc. Since you are getting spark (however weak), then I think your problem lies elsewhere. And no, you don't have to recalibrate the sensor since you took it out. You run into problems when you swap out computers/tunes, but yours should be fine. It only installs one way after all.

    These things are a PITA when trying to chase down a no start issue, but hang in there. You'll get it.
    Last edited by JJonesey; 07-16-2009 at 07:33 AM.
    1997 C1500 ECLB 5.7 Vortec G80 3.73 Rear
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    Re: 98 5.0L Vortec won't stay running

    I have no idea whether the P0336 code is current or a history code. I'm not that fluent with my newly acquired code reader.

    I ordered a cap and rotor, OE factory stuff, to put on when it gets here.

    My next check will be the coil, and then a compression check.

    Anyone know the proper PSI range for a compression check? If it is a head gasket, the compression should be real low on at least one of the cylinder banks.

    I have to out of town for a few days, so it's going to have to wait for now. If you all can come up with anymore ideas, I'll check them when I get back.

    Thanks again.

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    Re: 98 5.0L Vortec won't stay running

    I would also check the distributor gear, stock one is plastic and is know to crap out! happened to me on the road, truck just turned off on me..

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    Re: 98 5.0L Vortec won't stay running

    The stock distributor gear is not plastic, but they are known to wear excessively. I'm running out of ideas... Broken timing chain? Bad module? Weak coil? Faulty CTS (if it stinks like fuel and won't fire it could be reading dead cold, I had this happen on another rig - I guess it could read the opposite and maybe do the same). Can you get it to fire if you spray starting fluid down the throttlebody?

 

 

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