Bought the truck new in 1999.  It currently has in the neighborhood of 115k miles on it.  


Developed a miss and seemed like it was backfiring or at least running a lot rougher when cold.
Replaced the catalytic converter and it seemed to run a little better but still had a slight miss.

About 2 years ago it died on the way home one night and I ended up replacing all 6 plugs, Plug Wires, Distributor Cap, Rotor, and the Ignition Coil. The miss never quite went away...it was less noticeable during dry weather or on a warm engine, more noticeable in wet weather or a cold start.

Fast Forward to the curent issue:  Replaced the Battery (it tested out as bad)  2 weeks ago and had Autozone plug a Code Reader in due to a check engine light on and it running rough again. Code Reader spits out:
"Cylinder Misfire detected - Random Cylinders
Powertrain control module monitors the crankshaft speed and has detected a misfire condition.  
Probable cause:
Ignition system fault - spark plugs, ignition wires, coil
Vacuum Leak
Injector Fault
High or Low fuel pressure"  

Last week I went out to start it and it tried but wouldn't kick over.  The next day it would start but still had a miss and wouldn't idle.
 
I think I can eliminate the Ignition System.....they SHOULD last more than 2 years I'd hope (yes they were correctly installed and not mixed up)...but I'm not sure how to check the other stuff and can't afford to just hang parts until I get lucky.  Can anybody point me in the right direction?  I do have a manual for it (Haynes I think) but some of its directions are a bit vague.  I'm no mechanic but I do my own brakes and I'm fine with oil changes, and did all of the plugs and wires currently on it.

Thanks very much for any and all advice!

My wife has the same year Blazer and last fall I had the same problem.   We had to replace the Distributor.

You should also test the injectors, had to replace a few of those last year also.

I agree with VS on the distributor diagnosis.

thanks guys.  at least I have a direction to look in now.  I'll check the manual but I'm thinking this probably won't be a do it myself job.  it'll take me a bit to get the cash saved up to get it into the shop.

Do you have a spark gap tester?  They're cheap and have saved me a good bit of trouble in diagnosing IM troubles before.

is that the engine with the crappy fuel injection spider under the intake?

masfonos - I don't have a spark gap tester but after googling I can see where it would certainly come in handy.  

racinfast - I've seen a "fuel injection spider" mentioned on some of the chevy forums.  I've not had to take the intake off of my truck that I can remember so I can't 100% confirm but yeah I think it's the same engine.  Up until the ignition system problems it's been very robust and always had plenty of power with enough acceleration to pin you back in the seat even from 60mph.

Yes it is (CSFI).  I have a '97 and replaced the fuel injection system with an MPI version a few years ago.

http://forums.s-series.org/viewtopic.php?t=15105

Is it disappearing any coolant?

These engines are prone to intake manifold gasket issues..sometimes leak small amounts of coolant..sometimes just leak air..as in vacume leak at an intake port.

If the original intake gaskets have not been replaced with the new type gaskets..then this could be a good possibility as a cause for your problems.

I gotta make this quick but the dissy cap is most likely the cause due to faulty vents.....  Next inline of know problems is the dissy drive gear (I'd go after the cap as it will not last 2 years) is made to soft and well sucks.  Next any is most likely not your problem but will cause a P04XX (I'll look it up) is a faulty poppet on your CSFI and is cured by the MPFI update.

These motors are very sensitive to ignition parts.  Cheap aftermarket parts are a real problem, so only use GM parts.  Rockauto has cheap GM parts and so does amazon.

Check the fuel pressure readings.  you can rent a gauge or they are fairly cheap.  And you spider could be bad.  The poppet valves stick and leak.

Crank sensor?


Go here and ask you question.  There are some really knowledgeable GM mechanics there.

I think I did put an aftermarket Dist. cap on  it and I know the plug wires are.  I'll check the link above for the part and check it against Advance Auto.  They don't have it in stock locally but I can get free shipping to their store.  Kinda irritating that the original lasted for 9 years and the replacement won't make it 2.  Once the budget's got some wiggle room in it I'll try a Delco Distributor cap and see if that does the trick.  If it does I'll get the fuel injectors and other stuff checked as funds allow.  If not I'll probably let a pro put a distributor in it....it seems pretty straightforward as long as I can get to the bolts, but if I screw up the timing putting it in I don't have the equipment or experience to fix it.   Sundance I've been doing a lot of googling and lurking at the site you linked and learned quite a bit already.  

Thank you to everyone who has responded, I appreciate every bit of input.

I'll have to check on the coolant.  It's never run hot except when the water pump went out probably close to 5 years ago by now.

Since you shop at Advance here are some codes I posted a couple days ago.

 

Not to start a pissing match but you are not correct....  The factory "tin" and is just that dissy cap is junk, or as per the faulty vents (for moisture) in the factory dissy.  Brass aka aftermarket is a cheaper fix for this problem.  Two problem occur with this ignition setup either first the dissy condenses moisture and fouls the electrodes in the cap or second due to a outsourcing if the drive gear the dissy drive gear wears prematurely due the brinell (sp?) hardness vs the cam.  Thus excessive lash on the dissy usually will throw a cam correlation error via the PCM.  Next poppet valves cannot stick or leak they just build up shit, or break and are to be blunt junk.

OP go get a cap with brass electrodes from any auto jobber and make a PCR (planned component replacement) on a MPFI update along with a intake gasket update.  I've got a very detailed write up on these POS trucks and the TSB's and PCR's I can send you.  Yeah they are junk but I own a few and worked on hundreds.....  All in all good rigs just have some bugs....LOL

That's fine, but you are the first person I have ever had type that,  also my experience has told me different with aftermarket parts.

As to the poppets

CBS  News


From CARB:



From GM

Brief update.....

I haven't replaced any parts yet - haven't had much wiggle room in the budget even for a measley 50 bucks worth of parts, yeah it sucks.  

The important part is I threw it on the charger for a bit today to protect my battery and tried to start it just for grins.  It started.  

We've had several warm, clear, DRY days lately.  The initial refusal to start was during wetter weather.  The truck won't be going back into service as a daily driver until I've replaced the Dist Cap and Rotor and probably had the distributor checked, but I thought maybe the extra info might point one of you guys toward a more definite diagnosis.  

Thanks again for all the information so far.

My daughters blazer 1998 did the same thing ,was the wireing harness conectors .   Check them and see if they are corroded or have had lots of needle probes punched into them!

Bob