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1988 Chevy K2500 killing ignition modules.

This is a discussion on 1988 Chevy K2500 killing ignition modules. within the Technical / Maintenance forums, part of the General Discussion category; I've got a 1988 Chevy K2500 4x4 Silverado with 5.7L eng, automatic trans, A/C, P/S, P/B. I've had problems recently ...

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    1988 Chevy K2500 killing ignition modules.


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    I've got a 1988 Chevy K2500 4x4 Silverado with 5.7L eng, automatic trans, A/C, P/S, P/B.
    I've had problems recently with it killing ignition modules.

    I recently purchased & installed a NEW MSD distributor because of a stalling problem @ idle due to worn out, corroded, rusty, or weak magnets on the distributor shaft, replacing the dist cured that problem back in June.

    This NEW dist came with a new module, cap, rotor, etc.

    It's a new part from a reputable manufacture, so it's hard for me to believe it had a cheap module like ya can get from some of the auto part stores these days that sell parts made in China or Taiwan.

    Now I seem to be having a problem with ignition modules going out for some reason, 3 since June, less than 4 months now.

    I had to send the new dist back to Jegs for a replacement so I reinstalled the old dist after I removed the shaft & cleaned the rust from the pick-up coil & magnets, after reinstalling the stalling problem has not resurfaced.

    But again it knocked out the ign module that had been in the truck since new, 22 years.

    I replaced that module & last Saturday it went out again, less than a month on it, approx 300 miles, if that much.
    Oh, & yes I installed the heat conductive compound under the old & new module, so I know that's not it.

    I know without a doubt that all ground wires & other connections are good & clean, I ran these down trying to diagnose the stalling problem.
    I checked every wire & connector in the eng compartment & under the dash from front to back.
    It is a 22 year old truck so I checked it all out just to eliminate any other problems too.
    I've even triple checked, so I know that's not a possibility.

    Can anyone give me any clues to what is going on here.

    I'm & experienced motorcycle, ATV, PWC, outboard tech with over 30 plus years in the business.
    I've never worked as an automotive tech but I am very knowledgeable in the that area too, but I do have my limitations in some specific areas, I'm very technically inclined.

    I've been disabled since 1999 so I'm a little rusty on my tech skills, it takes me a little longer to do things these days than it used to.
    I may have been off the bench for 11 years now but I'm still a pretty quick study & very thorough in my work.

    I don't have access to any technical service hotlines that may shed some light on where this problem may be coming from so I'm asking for help from experienced auto techs & anyone else with more knowledge in automotive repair.

    So I'm asking for help if anyone has any ideas, please advise.

    Thanks, hi-tech redneck

  2. #2
    Loves GMT400 haters someotherguy's Avatar
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    Re: 1988 Chevy K2500 killing ignition modules.

    You did the right thing sending that MSD distributor back. I'll take a guess and say it's model # 8366? Google MSD 8366 problems and see what I mean. Some people have had OK luck with them by running a real GM module, but the fact is those distributors are bad news. You'd think you could get a good product by going with a "trusted" name, but that 8366 is junk.

    If you suspected your original distributor, and now it's reinstalled and still having problems - I'd replace it with another OEM distributor, especially if the magnets seem very weak. They're not very strong to begin with, so it may be hard to tell for sure if they're bad unless they have no real magnetism at all (or are broken.)

    A distinct possibility is the coil may be bad, but I can't really tell you what the probability of it would be.

    I'm not a fan of most parts-house brand ignition parts; even the "big names" like Borg Warner. Even the top-line NAPA stuff is often chinese-made anymore, though it doesn't hurt to go down there and check it out for yourself. Their cheap-line stuff isn't worth buying, might as well gamble with Vatozone or Pest Boys at that point.

    On the subject of the heat sink compound / "thermal grease" - more is less in this case; some people goop it on - not saying you did - but a thin layer is what is best. Too much acts more like an insulator than helping with heat transfer. It's best to clean the surfaces well and apply a new thin layer of the stuff when installing a new module.

    I'd also check the grounds around the engine. Most important would be the rear passenger head ground strap to the body; goes to the firewall just under the heater hoses. It gets corroded kind of easily, or gets broken / left off if the engine has ever been out and the installer missed the strap.

    Richard

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    Re: 1988 Chevy K2500 killing ignition modules.

    tbi distributor 101:
    the four post connector to the distributor:
    pin A: reference ground low, may be ground to distributor, it makes sure the ground circuit between ecm and module. if open may cause poor performance.

    pin B: bypass. at about 400 rpms the ecm applies 5 volts dc to this circuit to switch spark timing control from the module to ecm. an open or grounded bypass circuit will set code 42 and the engine will run at base timing,
    plus a small amount of advance built into the module.

    pin C: distributor reference high. this provides the ecm with rpm and crankshaft position info.

    pin D: EST. this circuit triggers the module. The ecm does not know what the actual timing is but it does know when it gets the reference signal. it then advances or retards the spark from that point. therefore if base timing is set incorrectly the engine spark curve will be incorrect.

    results of incorrect est operation:

    low map output voltage: more spark advance
    cold engine: more spark advance
    hot engine :less spark advance
    high map output voltage: less spark advance

    detonation can be caused by high map output or high resistance in the coolant temp sensor circuit.

    poor performance can be caused by high map output or low resistance in the coolant temp sensor circuit.

    wire diagram:http://i40.tinypic.com/330d6y9.jpg

    ensure the module screws are grounding module to distributor base.

    the two pin connector on the distributor(C and +) should have battery voltage there. low voltage would indicate an open or a high resistance circuit from the distributor to the coil or ignition switch. For example If C terminal voltage is low and + voltage is 10 volts or more circuit from C terminal to ignition coil(coil primary) is open.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 1988 Chevy K2500 killing ignition modules.

    also, arcing coil, plug wires or cap can hurt the module
    ASE Master Certified Technician

    2000 Silverado 6.0 4L80E 2wd
    *RIP*1994 Z71 SCLB 355, Dart Heads, 10.5:1 CR, PM rods, CC XR270HR

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    Re: 1988 Chevy K2500 killing ignition modules.

    Thanks for the info.

    Well it seems that did I receive a defective MSD distributer from JEGS.
    But I'm now led to believe I have another problem too that may have caused it's premature failure.

    The day after I submitted this post about killing modules on 10-1-10, I reinstalled the DIST out of my '94 Yukon that I have stored for the last 10 years trying to preserve it until I have the health & money to rebuild it since it's got over 378,000 original miles on it now & still looks new since the day I bought & ordered it.

    Well I've been driving the '88 K2500 since on the original module that was in the '88 dist.

    I didn't have any problems until yesterday coming back from my shop in the next town that's 30 miles away.

    To try & make a longer story not so long, (I hope). lol
    The truck died while driving down the hwy @ 65+.

    I pop the hood & check it out to find no fuel injection, I get no NEG impulse to pulsate the injectors.

    I've got +12 volts on the red & white wires of the injector connections, this is tested by volt meter to the unplugged INJ connectors & ENG ground.

    My understandin' is the ECM picks-up a signal from the DIST IGN Module or coil and then sends a negative impulse signal to fire the INJ.
    Do I understand this correctly?

    I've got spark on all 8 cyld's, it'll start & run if I'm supplying fuel manually by pouring it down the TBI unit or by applyin' power to the INJ myself.
    I apply voltage to the INJ via a wiring apparatus where I can manually turn power on & off (tapping) so the injectors don't steadily spray fuel.
    That eliminates fuel press (which is @ 13-15 lbs), spark, fuel supply from tank, eng condition & anything else it needs to make it run, well all I can think of anyways.

    I had a new ECM & Module delivered, of-course that didn't help to change those either.

    I checked the Green & Dark Blue INJ wires between the TBI & the ECM (pin #'s D14 & D16) & have no broken wires or shorts to a ground either.
    Of-course I've got POS +12 VLT's on both the Red & White INJ wires with the key on, so no blown fuse on that side of the wiring.

    Yesterday, Tuesday.
    I checked the TPS sensor with my DVOM & the TPS is fine.
    I checked for voltage @ the TPS & MAP sensor 3-wire connectors & have no voltage between any of the wires in the 2 connectors, a total of 6 wires.
    Shouldn't I get 5-6 volts here?

    I grounded the DVOM's Negative lead to the ENG & probed the wire terminals with the Positive lead.
    Like I said no voltage.

    Well it got too cold for me to do anymore diagnoses to the 'ol blue truck so I'll have to follow up in the mornin', weather permitting.
    It was 70+ last night & 11pm, this morn it was 36 with a high of 49 so it was too much for the 'ol injured & now 'cause of this, sore back & all the metal in me now. I hope y'all understand.

    Well, I'm replyin' (I hope) to you because you seemed very knowledgeable with the reply on my first posting about the killin' of the modules.

    So I'm askin', can you give me any ideas what to check on to find this problem or problems.

    I'm kinda limited on wiring schematics since all I've got is a Haynes repair manual now.
    I had a full set of GM manuals for this rig but my daughters little hubby stole them from me when I let them live in the house awhile back, well I assume he did since he did steal several other things from me too all around that same time.

    Not hard to put 2 & 2 together since nothing has come up missin' since.
    Of-course they are not allowed around my house because of all of it.
    But I'm sure y'all don't care to hear about that too.

    So if ya can get me some wiring schematics too that might help.

    Thanks in advance.
    Hey I see you have a bike on your profile, if your a rider & ever need any tech help on the M/C I've got an extensive service background in the M/C field & will be more than happy to help ya out if I can.

    Hi Tech RedNeck

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    Re: 1988 Chevy K2500 killing ignition modules.

    Right, the ECM gets the signal from the module and grounds the injectors to fire them.

    I'd go back over what I suggested, and also what Dave said. Are all your engine compartment grounds in top notch shape?

    Appreciate the offer of help on the scooter, might need it, might not. You never know. I've been riding shovelheads since 1995 or so, and unless you're rich, you have to know something about maintenance/repair to keep an old bike on the road. And the rich guys generally don't ride old bikes. Just ones made to look old.

    One thing Autozone has been good for (and only one) is that their site had some wiring diagrams online, dunno if they still do. You have to register (free) in order to view them; they're under the "repair help" link. All the ones I saw were from factory manuals.

    You can also hit the library as they probably have them as well.

    Richard
    Last edited by someotherguy; 12-01-2010 at 01:10 PM.

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    Re: 1988 Chevy K2500 killing ignition modules.

    Check the charging system for excessive charging over 14.3v for an extended time.
    04 K1500 Silverado EXT 3:73 gears, 5.3L 265/75-16,Pace Edwards tonneau,

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    Re: 1988 Chevy K2500 killing ignition modules.

    Redvett, would the motor have to be runnin' to check for charging over voltage.
    And no the system is charging @ the service limits when it is running.

    I already thought of that.

    Thanks though.

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    Re: 1988 Chevy K2500 killing ignition modules.

    All the ground terminals on this truck are good. That's the 1st thing I checked.
    Especially the ground at the T-stat housing.
    I actually don't use that area for the 4 GRD wires that connect there.
    I use a open bolt hole near that location in the I-manifold where I install a stainless star washer & bolt, I find this pretty much eliminates corroded or weak grounds on these trucks.
    The factory location is a weak link in my opinion.
    So that ground is very solid.
    All the other ground wires are clean & solid too, back of MTR to firewall, near the steering column area, etc.

    Now after I was able to do a few test's this evening I have found that I've got .58dcv on the TPS Gray wire & .79dcv on the MAP Purple wire, & no voltage on the CTS Yellow wire.
    This was done with all sensors disconnected @ the same time & the key on.
    I have 12dcv @ C16 on the ECM connector's Orange wire. Key on or off.
    I have a good GRD @ D6 on the ECM's Tan wire also.
    I have good GRD on the TPS & CTS Black wires & on the MAP sensors Purple wire.

    So I'm thinkin' I'm loosing voltage to the sensors which have good wires as per the test between the terminals @ the TPS, MAP & CTS connectors & the ECM connectors.
    No open circuits & no shorts to ground.

    I've removed all the wire looms from the wiring harness in the ENG compartment to see if I had any melting or chaffed wires. None

    If y'all could see what I'm working with ya wouldn't believe this is a 22+ year old truck.

    Also having the M/C tech background I keep everything very well maintained.

    Especially the truck I use to pull my boat, I hate to miss on good fishing weather so I try to keep 'ol blue in top condition, well as top as I can. lol

    What I need to know is where do these sensors get their power from?
    Are they switched thru the ECM from the IGN switch?

    I'm kinda limited on the wiring schematics, but I'll check out AutoZone's website as per someotherguy's post.

    As for Daves info, the symptoms would be easily noticed, especially by me when I drive.
    Y'all know how it is since your car guys too.
    You get a feel for a vehicle & you can tell if it's got a problem or losing power for some reason or another.
    This truck runs like it should until this particular problem shows up.
    I can usually tell when a rock get stuck in the tires.
    Besides, I would see arcing from leaking voltage from a faulty IGN system when I have the hood up in the dark when it's running, this is quite often by the way, or I'd feel a miss especially when pulling a load as heavy as my boat.

    I used to crew for a top alcohol dragster 3 man team.
    Along with being a Motorcycle tech for 30 years I'm pretty good with using know good parts & always quality parts on all my vehicles.

    The IGN system is all MSD. Dist assy, Coil, & wires.
    My opinion, they make better quality IGN components than OEM or aftermarket auto parts retailers.
    Other than the defective Mexico made MSD dist I got from Jegs everything else in the system is in good condition.
    I'm now using a known good OEM dist.
    MSD assured me they corrected the manufacturing problem on these distributors, so I guess we'll see when the new unit arrives.

    That is if I can get this problem figured out.

    I'm suspecting a electrical supply to the ECM that is switched or there's another sensor that has shorted out & is pulling the low voltage supply from the sensors I've mentioned above, keeping the voltage from getting to where it should go causing these symptoms.

    What terminals or wires should be switched on the ECM?

    Just remember this truck will crank and run if I'm supplying the fuel manually.
    So wouldn't that eliminate any suspicious IGN components?

    Thanks for all yall's input.

  10. #10
    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 1988 Chevy K2500 killing ignition modules.

    you should have 5vdc on the yellow wire coming from the ecm going to the cts sensor. ignition on engine stopped wire disconnected from sensor.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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  11. #11
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    Re: 1988 Chevy K2500 killing ignition modules.

    the sensors get there 5vdc from the ecm. 12vdc is usually from the ignition switch/fuze ie injectors and ignition coil.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
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