95 blazer LS 4.3 4x4

So, I replaced my spider, nut kit, and gave it a full tune up, and a host of other things, and the car was running good for about a month. Then the same thing happened all over again, I was on the freeway going home the car started to sputter and then cleared up, but when I got to a stop light the car die! After about a few minutes of trying I finaly got it started and limped home! The next day I tryed to start it, it would turn over fine, but would not start! It showed no signs of firing at all! I let it sit for a few days, and tryed to start it again. It fired up and idoled for about a minute, and then died, and would not start after that, with no signs of firing at all!

The days have been pretty hot lately, so could this be a fuel pump issue? I did all the fuel presure checks, 60lbs pump on, over 50lbs for over 10 minutes! Pulled the plenum off and checked for any leaks. (none) used a noid light to check to see if the spider was getting a signal, (it was) checked each poppet to see if they were firing gas, (each one was) Checked to see if the spark plugs were firing (they were)! By the time I had done all these checks, the sun had started going down and it was cooling off a little.

If I'm getting gas, and getting spark, shouldn't the car run, even if it's running poorly??? The only odd thing I noticed, was inside the plenum on the left side there was oil, in the plenum and the ports, but only on the left side, Could this be a sign of a blown head gasket, or maybe a cloged PVC valve? Even if it's a blown head gasket, shouldn't it still run or at least try to fire?

Do fuel pumps go in and out when they get hot and cool off? Can pumps have presure, but not enough volume?

 

Yes fuel pumps can go in and out when they are in the early stages of failing. And they can have adequate pressure, but low volume.

Test the fuel pump output pressure. Connect the diagnostic gauge at the fuel filter, disconnecting the line to the engine. There's some debate as to whether to use the outlet fitting on the filter or the fitting on the pipe at the inlet. I won't argue religion and faith here, connect the gauge so that the fuel flows from the pump to the gauge and stops there, not to the engine. Prime pressure should be over 70psi (I don't remember the exact number but it's in the 70's) and could be as high as 100+ psi. After the prime cycle (a few seconds), the pump will stop and the pressure will drop some. Pressure should hold over 60psi for 10 minutes at the pump (testing at the filter).

Are you getting spark? With the fuel pump relay out (you don't want it to start during this test), pull one plug and set it on a metal part of the engine (#1 plug on the AC compressor bracket works) with the plug wire attached. You want the metal base of the plug grounded to the engine, that's the point of setting it on a metal part. Have someone crank the thing and watch to see if the plug is sparking.

To run, the engine needs fuel, spark, and something close to the right timing. If it doesn't start at all, one of those three things is wrong.

Oh, and is the SES light on? Any DTC's present?

 

SES light not on. Checked the fuel presure and it is good. checked the spark at the plug and it is good. checked the poppets and they all are spraying gas. It would seem that when the car cools down the problem goes away! What of these parts if any would stop working when they got hot, and work again when they cool down? FUEL PUMP, SPIDER AND POPPETS, COIL, SPARK PLUGS? It's hard to check the spider and poppets when hot, because it takes time to remove the the plenum, and once it's removed you can't start the car to heat them up! What would be a sign of low fuel pump volume? What could affect the timing, I havn't done anything to affect it myself! If it starts up and runs for a few minutes, then dies, does that mean the timing is OK? Is there anyway the O2 sensors could keep it from starting?

Does anyone have a link to a video on how to cut a hole in the frame to get to the fuel pump from the top on a 1995 Blazer?

 

If it's running rough only when it gets hot, I'd lean more towards the coil, or the amplifier/driver "module" on the coil bracket with the coil.

One way to test is to carry some of that electronics cleaner "air in a can" or "freon in a can". When it starts acting up, pull over, turn the can upside down and hose the coil and/or the module down with the very cold liquid and start it up. If that works around the problem, you've found the component(s) that are malfunctioning when hot. Do one part at a time. It's also possible the thermal shock from this "test" can damage/kill a weak component. If that happens, you're probably more likely to kill the part that's already failing, but there is no guaranty.

The fuel pumps can have heat issues as well, but they are submerged in the tank, and shouldn't overheat. If it's the fuel pump with thermal issues, the problem will go away or be much less pronounced when the tank is full than when it's near empty.

 

It doesn't run at all when hot! Is this a common problem with the coil and module? My car has spark, but it dose seem weak and it's a yellow color. Shouldn't it be blue?

 

What you are describing is sounding more like the coil or maybe the module.

Check the coil with an ohm meter, if possible, right after it dies. If yours has the old style coil, with the high voltage terminal that looks like the top of a spark plug, the resistance on the low voltage side (primary) should be 0.3 to 1.3 ohms. The high voltage side (secondary) should be 5K to 10K ohms.

If you have a late production, OBD-II model, I'm really curious which coil you have. OBD-II models will have the words "OBD II certified" somewhere on the emissions label on the fan shroud, and will have the PCM mounted above the coolant recovery tank under the hood. IIRC, the OBD-II 1995's had the later coil, with a high voltage terminal that looks just like the posts on the dizzy. That coil should be 0.2 to 0.5 ohms on the low voltage side and 5K to 25K ohms on the high voltage side. If you have an OBD-II 1995 model, I'd really like to know which coil you have.

I've seen flakey modules that misbehave like this, but that's rare. The modules usually just work until they stop working (like someone turned the key off), and then they never work again.

And yes, the spark should be blue and fairly strong. A weak coil or poor condition plugs can also cause different color and weaker spark. How old are the plugs? What's the gap measure?

 

Sorry took a day off to have some teeth pulled!

I have the OBD-II 1995 model. But have the old style coil that looks like the end of a spark plug. My car is a half breed, half 94, and half 96! Sucks!! Could the module in the top of the dizzy go in and out with the heat, and would it have this affect? I havn't check this yet, but if the spark strait from the coil is blue, but the spark at the plugs is yellow, what would that mean?? The Cap, Rotor, plugs and wires are all New! All A/C Delco, plugs platnum! Gap .45

Havn't been able to check anything yet, because of having my wisdom teeth pulled, I'll try to get back at it on monday! Thanks for the help!

 

No problem. I hope you get feeling better soon.

I'll be offline for a bit starting later this afternoon with some unscheduled travel and personal business.
Not really. Spark is triggered and timed by the crank position sensor only. The only participation at the dizzy is getting the spark to the correct plug wire. For that, the rotor has to be in the correct position (precisely).

You can set the dizzy position with a good scan tool, watching the live datastream for the PID "CMP Ret" (Cam position sensor Retard angle), sometimes called "CMP Offset" Or something similar. That needs to be as close to zero as possible, the official spec is zero +/-2.0°. You adjust that at the dizzy. The stock clamp is like a wrench, and doesn't allow the dizzy to turn much. You can drill out the hole for the tie down bolt in the stock clamp, allowing some movement there, or you can remove the stock "wrench" style clamp and install an older clamp for a small block Chevrolet (like the Mr. Gasket 1009, widely available for $7 or less). The older style clamps allow for adjustment.
That would be caused by high resistance in the cap and/or rotor, or by an improper CMP retard/offset angle (the rotor not in full contact with the cap post for the plug).
Good luck with it, and good luck with your recovery. I had wisdom teeth and one molar removed about 10 years ago. You're going to be hurting for a few days.

 

Haven't been able to get back at it yet, but have another question! I think this is a different problem, but not sure.

When I pulled the plenum off, I noticed a few puddles of oil in the intake next to the poppets on the passenger side, and the ports on the passenger side threwout the plenum were covered with oil also. I pulled the plugs and #2 and 4 plugs had some oil on them, but not fouled. Did a comprestion test, and all the cylenders had between 135 and 145 lbs of presure ,and held that presure for for at leased 5 minutes or more. What could cause this? It's on the side where the PVC valve is. If there was a blown head gasket, wouldn't it have low presure, and not hold presure after it built up? Could it be bad vavle guides, or a blown intake gasket on the inside of the lower intake? Because of vaccum, air should only flow one way, from the air intake down through the plenum, into the lower intake, and then into the heads! So, in order to have oil in the plenum, the oil would have to be sucked through the PVC vavle into the plenum.? Is that right, or if the lower intake gasket is blown, could it blow oil back up into the plenum?