i loaned my '97 blazer (see signature) to someone for a couple months and while it was gone it developed a misfire. when i first found out it was misfiring it was throwing a random/multiple cylinder misfire code. i cleared the codes and drove the ~50 miles home, checked again and it was reporting cylinder #2 misfire. since then it hasn't been throwing any codes (the CEL does not work), but it is still misfiring. it has gone through several tanks of gas (different gas stations) and some fuel injector cleaner.

are there any common problems with the '97s that i should look for, or should i just start with normal troubleshooting? (plugs, wires, cap/rotor, fuel filter, etc.)

what's really bugging me about this is that the person i loaned the truck to ran it out of gas. the price of a new fuel pump for this thing is nauseating.

 

Well at least they were honest enough to tell you that they managed to suck all the crap from the bottom of your fuel tank through your fuel injection. Can't be good.

 

it wasn't entirely her fault... the gas gauge swings all over the place.

i don't know if it was misfiring before she ran it out of gas. it wasn't happening when i still had the vehicle.

 

You might want to check the compression on #2 cyl and maybe a couple of others to compare.
My first thought would be crap in the fuel injector though.

 

i bought a fuel filter, it was cheap enough and probably needs to be changed anyway (i bought the truck in february, not sure about previous maintenance). hopefully the pump just sucked up a bunch of crud and clogged the filter. do these pumps have a sock filter?

if the filter doesn't fix the problem i'll look into doing a compression test to see if any of the cylinders are lower than the others. i'm kind of gunshy about the loaner gauges from zono, though - had a couple of bad experiences. what kind of compression should i be seeing on a ~100k mile 4.3?

also, i forgot to mention - it doesn't seem to misfire all the time. sometimes it's really bad, sometimes it's barely noticeable, sometimes (most of the time) i don't feel anything.


edit:
noob question, please bear with me: how do i release the fuel pressure?

 

Engine Compression Test
Ensure that the vehicle batteries are in good condition, and fully charged.
Operate the vehicle until the engine is at normal operating temperature.
Disconnect the positive ignition coil wire plug from the ignition coil.
Disconnect the fuel injector electrical connector.
Remove all of the spark plugs.
Do not insert objects into the throttle plate opening. Damage to the throttle body can result, requiring replacement of the throttle body assembly.

Block the throttle linkage wide open.
Install the engine cylinder compression gage to the cylinder being tested.
Using the vehicle starter motor, rotate, or crank the engine for 4 compression strokes, or puffs, for the cylinder being tested. If the engine rotates for more than 4 compression strokes, test the cylinder again.
Record the compression reading.
Remove the engine cylinder compression gage from the cylinder being tested.
Repeat steps 8-11 for each additional cylinder. All cylinders must be tested to obtain valid test results.
If any cylinders have low compression, inject approximately 15 ml (1 oz) of engine oil into the cylinder through the spark plug hole.
Repeat steps 8-11 for all low compression cylinders.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kpa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). Multiply the highest cylinder pressure by 70 percent, 1035 kPa x 70 percent = 725 kPa (150 psi x 70 percent = 105 psi), in order to determine the lowest allowable pressure in any other cylinder.
- Normal The compression builds up quickly and evenly to the specified compression.

- Piston rings leaking Compression is low on the first compression stroke. The compression builds up on the following strokes, but does not reach normal. Compression improves considerably when you add oil.

- Valves leaking Compression is low on the first compression stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil.

- Head gasket leaking Compression is low on the first stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil. Adjacent cylinders have the same, or similar, low compression readings.

If one or more cylinders fails to meet the minimum specified compression, repair or replace all damaged or worn components and test the engine again.

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Remove the gas cap, then put it back on
Remove your fuel pump fuse and crank the engine to relieve your fuel pressure

 

On the fuel line by the firewall there is a small black plastic cap unscrew that cap and find something like a philips screw driver (with a rag rapped around it to catch any gas spray) push in on the center and it should relieve the pressure. another thing to do is to remove the gas cap to remove pressure from the tank..

 

well, i kind of narrowed the problem down to mostly occurring when it's raining. and i think i might've found the problem:

http://magtec.rvglug.org/misc/blazer/97/IMG_1401.jpg
http://magtec.rvglug.org/misc/blazer/97/IMG_1402.jpg

by the way, what's that plastic clip on the fender supposed to hold?


edit:
wait, i think i figured it out. judging by pictures i'm finding online it looks like there's supposed to be a plastic cover over that entire area. am i right?

 

nice camera, good close ups

 

If you look at the photo carefully there is another clip like the one you ask about, it is under the yellow/blue connector. There is another connector laying next to it might fit on the clip that has nothing on it...check the back of the loose yellow connector.