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87 K5 Blazer trouble start and missfire at full acceleration

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Old 05-08-2009, 11:01 AM
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Default 87 K5 Blazer trouble start and missfire at full acceleration

I have a 87 Blazer with a GM crate 350 TBI. The trouble is that when I start it up after it has ben sitting for a few hours, it will start after it turns over 7 or 8 times and before it reaches a resting idle speed the rpms will then drop and stumle back to idle, drop and stumble back to idle, and so on for about 4 times before it actully finally reaches a steady resting idle speed. After that it idles fine. It will also misfire 1 to 2 times in a row on full accelleration. It only seems to do this when I give the throttle 3/4 pedal or more. On last possibly related querk is that is does not stumble when accellerating from a stop but it does seem to hesitate, and lack power at very low rpm take off's. I have replaced the coil, plugs, wires, cap and rotor, fuel filter, new battery, all in an attept to fix this but it remains. Any help would really be appreciated...Thanks in advance. Stephen
 
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Old 05-08-2009, 03:52 PM
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Clean your throttle body thoroughly. Also replace the base gasket as they have been known to leak.

If you have not done so yet, clean the EGR valve, but be careful not to get any cleaner onto the vacuum diaphragm.
 
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Old 05-11-2009, 07:09 AM
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Thanks swartlkk,

I will be trying those imediately. One thing that I forgot to mention is that when the previous owner took out the smog pump he also took out the EGR solenoid, but kept the egr and plugged the vacuum lines on the TBI and the egr valve. He did the same for the charcoal cannister. I am not sure what he was thinking. Could the EGR not being functional have anything to to with the conditions I described as well?
 
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Old 05-11-2009, 11:30 AM
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The EVAP and EGR systems, if properly capped off and sealed up, should not impact engine performance all that much. Hopefully the cat is not the stock unit as the pellet type catalytic converters are highly restrictive and need a functioning EGR and smog pump system to keep them cool and operating properly. If you have a newer grid style converter (or none at all), you should be ok. Tampering with any of these systems is prohibited by federal law though...
 
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Old 05-11-2009, 11:33 AM
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Hey Maumelle...used to live right near you...NLR
 
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Old 05-11-2009, 12:42 PM
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Pretty sure that my cat is the original. It still has the u-bolts and the keyed in notch on the inlet and outlet pipes. Should be easy to replace. Could it really be causing such serious problems, or enough back pressure to cause them?
 

Last edited by sac34; 05-11-2009 at 12:48 PM.
  #7  
Old 05-11-2009, 12:47 PM
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Another strange thing is that the truck will throw the fault 32 (EGR) trouble code after a few miles of driving, even with the EGR solenoid removed and the electrical leads unplugged. On this one I am really stumped.
 
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Old 05-11-2009, 01:36 PM
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It probably is looking for a change in MAP output when it signals to open the EGR valve. The only way to get rid of that is to program it out of the ECU.
 
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Old 05-11-2009, 02:06 PM
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Those Cat's are bad about cloging up you can test it drill 2 holes one pre Cat the other post weld on a bung and get the pressures. You dont have a chip on it do you? I have seen this alot on motors that have been running a performance chip.
 
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Old 05-14-2009, 10:59 AM
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Default Ran a few things down, still need help

Well, I have replaced the missing EGR solenoid, and vacuum lines and the EGR systm seems to be working fine...no more trouble codes either.

I have taken care of the catalytic converter issue, because by some miracle, it is now MIA and replaced with a 3-inch pipe.

I have checked the TBI unit gasket and it seems to be sealed up just fine. As best I can tell all of the vacuum lines are in good condition and the rotted ones I have replaced.

However I am still getting the missfiring at medium to heavy acceleration, and a chugging (idle drops almost enough to kill engine then cycles back 4 or 5 times before leveling out) at cold startup, as well as relatively sluggish power throughout rpm range. I am curious now if I might have a weak or bad fuel pump, bad TBI unit, or bad ECU. Just tough to reason these symptoms out to make the best next move. I have replaced the fuel filter already, and complete tune-up, new TPS...where should I spend the money in the best place next? Kinda getting tight on cash at this point. Surely a weak alternator could not cause these problems could it...I say that because the headlights and interior lights due pulse bright to dim at idle so I know it will go at some point. Could my ignition control module be the culprit, or are those not prone to failure?

Thanks for all of your great ideas and help.
 

Last edited by sac34; 05-14-2009 at 01:06 PM.

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