idle misfire, scope says its random

[Max Crax]

My 1996 Jimmy is awful in traffic. It has new Delco wires, Champion platnum plugs, Mobil 1, distrubutor cap and rotor, recent pro fuel injection cleaning, and lots of opinions as to what is going on (fuel pump, sensors, injectors, air leak, etc.). It is flooding, everyone agrees and it has cooked the converter. Cold starts are immediate, hot starts tough. Highway performance is fine, fuel economy primarily highway averages 18 mpg.

The most recent visit to a shop came up with I think it has to be in the intake, but the random misfire indicates something other than the "spider".

Could I get some experienced advice?

[BlazerLT]

You don't have a spider, they were killed in 1995.

Have your fuel pressure checked with the key on and the engine off.

It should be between 61-66psi.

[Max Crax]

Originally Posted by Max Crax

My 1996 Jimmy is awful in traffic. It has new Delco wires, Champion platnum plugs, Mobil 1, distrubutor cap and rotor, recent pro fuel injection cleaning, and lots of opinions as to what is going on (fuel pump, sensors, injectors, air leak, etc.). It is flooding, everyone agrees and it has cooked the converter. Cold starts are immediate, hot starts tough. Highway performance is fine, fuel economy primarily highway averages 18 mpg.

The most recent visit to a shop came up with I think it has to be in the intake, but the random misfire indicates something other than the "spider".

Could I get some experienced advice?

I will have the fuel pressure checked today. If it is unacceptably low, is the fuel pump normally the culprit (after fuel filter)?

[Max Crax]

Thanks for the advice. Judging by this site, fuel pressure is the most common problem on these vehicles.
Sounds like the fuel trickles instead of spraying at idle due to low pressure due to possibly low voltage, obstruction or failing fuel pump, right? New fuel pump has been recommended by 2 shops, but I thought that either it worked or it did not work...

[BlazerLT]

Did you find out the pressure yet?

[Max Crax]

Originally Posted by BlazerLT

Did you find out the pressure yet?

I spoke with the mechanic who scoped it - but he did not test it, so I need to know where to connect the pressure guage to check it myself.

The garage guy still says it has a spyder, which makes me a little leary based on what you said. The forum seems to indicate there are a lot of wiring problems repaired at garages by replacing expensive pumps and things, so I want to get in on fixing it right, as economically as feasible.

[amac209]

a lot of jimmy's seem to get moisture in the distributor cap. take it off and blow it out with compressed air. if that doesn't fix it try removing the egr valve and cleaning it, they seem to get gummed up and stick a little bit. i don't know what shops you have been going to but a gm dealer has access to lots of information and a lot more experience with your vehicle than independent shops

[BlazerLT]

Originally Posted by Max Crax

I spoke with the mechanic who scoped it - but he did not test it, so I need to know where to connect the pressure guage to check it myself.

The garage guy still says it has a spyder, which makes me a little leary based on what you said. The forum seems to indicate there are a lot of wiring problems repaired at garages by replacing expensive pumps and things, so I want to get in on fixing it right, as economically as feasible.

The fuel pressure schrader connection is at the back driver's side of the engine where the fuel lines enter the upper plenum.

You will have to remove a cap like on your tire valve stem to get access to the screw fitting.

[Max Crax]

Originally Posted by BlazerLT

The fuel pressure schrader connection is at the back driver's side of the engine where the fuel lines enter the upper plenum.

You will have to remove a cap like on your tire valve stem to get access to the screw fitting.

I have located the screw fitting. My vaccuum/pressure gauge does not have any fittings. Is the adapter a readily available item at CarQuest or similar places? Or do I need a special gauge to test?

[Max Crax]

Originally Posted by amac209

a lot of jimmy's seem to get moisture in the distributor cap. take it off and blow it out with compressed air. if that doesn't fix it try removing the egr valve and cleaning it, they seem to get gummed up and stick a little bit. i don't know what shops you have been going to but a gm dealer has access to lots of information and a lot more experience with your vehicle than independent shops

I had the cap and rotor replaced 2 weeks ago by a shop, and the points on the old cap were pretty bad. Now the truck starts easier but still idles rough like 1 or 2 cylinders are not firing regularly at idle, but joining in as rpms pick up to 1500 or so. The EGR - located on top of the intake? My egr past experience was removal and seal the hole (before OBD2) on inline engines! I can try cleaning the egr and testing fuel pressure to at least get direction on what needs fixing.

I was also considering hotter heat copper plugs in place of the champion platinums that have 5000 miles on them.

[BlazerLT]

1.) Have you ever changed the fuel filter?

2.) Get the fuel pressure checked with a fuel pressure gauge.

3.) Suggest going to AC Delco Platinum plugs gapped properly.

DO NOT START INSTALLING HOTTER PLUGS.

[Max Crax]

Originally Posted by BlazerLT

1.) Have you ever changed the fuel filter?

2.) Get the fuel pressure checked with a fuel pressure gauge.

3.) Suggest going to AC Delco Platinum plugs gapped properly.

DO NOT START INSTALLING HOTTER PLUGS.

Fuel filter was changed 8000 miles ago. I still have the old one which does not seem to be plugged when air is blown through it.
I will buy some Delco plugs to replace the Champions.

[BlazerLT]

did you check the fuel pressure yet.

[charleseich]

Cracked distributor cap OR cracked COIL. Check for arcing. It took me quite a while to find the cracked coil as the problem was intermittent, only happening when damp outside.

[Max Crax]

Originally Posted by charleseich

Cracked distributor cap OR cracked COIL. Check for arcing. It took me quite a while to find the cracked coil as the problem was intermittent, only happening when damp outside.

I have replaced the cap and rotor. Starting is much better. How did you discover the cracked coil?

If fire is good, the engine should not miss. If coil is good, everything else is new AC DELCO, so either the computer is confused or it is a fuel injection issue, right?

I have been trying in vain to have a garage test fuel pressure. I am just going to have to buy my own dadgum gauge and do it myself. If it is fuel - either too much or not properly sprayed, that might result in idle misfire...