Drove the Blazer about 8 miles, runs fine cruising down the road, probably lacking some power, and idles rough and lopey, and did stall out on me once at a stop.

I know too much unfortunately as I do work there.. far as distributor caps go the "Gold" gets you the "upgraded" brass contacts, the cheaper ones are aluminum AFAIK. "Gold" cap and rotor were $27, and wires were $17 for the Duralast, but after the fuel press test I didnt bother getting them.

While there I grabbed the fuel pressure test kit and ran a test, could only get the needle up to about 25psi and it would immediately fall down to about 5psi and hold there.. tried three times same result each time.

Bad fuel pump?

 

It technically shouldn't even be running if the pressure is only 25psi... The only true way to tell whether it is the pump or regulator is to also perform the test at the fuel filter, dead-heading the pump with the gauge. The process & parts required are listed in the tech article on the subject (link in my signature below).

 

Can I assume that the regulator is fine since the overall running condition of the truck has not changed much from the previous one I took out yesterday? They could both be bad, I understand that, but I dont have the vehicle much longer to work on, its going home later today, and I will probably get it back next week sometime if owner wants me to do the pump.

The new spider unit and plugs both helped, but were not the cure.

Fuel pump and filter were changed in late 08 Im told. Should I throw a new filter on today just for the hell of it and see if there is any change?

List of what Ive done so far:

new spider unit
new nut kit
new pcv
new plugs(delco)
cleaned iac
cleaned t/b
fuel press test: ~25 falling to ~5 within 3 seconds

 

The reason I say it is theoretically not possible is because the poppet nozzles used on the CPI engine are very pressure sensitive. If the pressure isn't >50psi, they shouldn't open.

If you make the assumption that all of the potential leak paths inside the engine are fixed, then, barring external line leaks, the pump is the only other thing that could cause the symptoms. But that is a strong & risky assumption given the CPI engine's notoriety for issues with leaks inside the plenum.

A new filter isn't going to hurt anything and it is cheap so that could be your next step, but I would try to get together the adapters necessary to connect your fuel pressure gauge at the filter & dead-head the pump as this will give definitive proof concerning the pumps health.

Also, if you have access to another GM vehicle or, better yet another blazer, test the fuel pressure to make sure the gauge is working properly.

 

Hmm, I dont have the pressure tester with me, just used it in the parking lot at work so I didnt have to shell out the $150 deposit to rent it.

Do the loaner/rental test kits have those adapters? Or is it something you have to custom build like the picture in the link you referred me to in your sig?


edit: One thing I have not mentioned is that if it doesnt start on the first try, then it will crank over and doesnt want to fire unless I give some throttle input to get it started, after it sat over night it started right up this morning, after driving for ten minutes and the fuel press tests I had to crank and apply some throttle to start it.

This is a sign of a bad pump to me, and actually was the first thing I mentioned to the owner, but I figured it was the cpi unit.

 

You pretty much have to put things together to mate up with a typical fuel pressure gauge set for testing at the filter inlet.

To me, it sounds like there is still a leak in the plenum creating a rich condition...

Did you pressurize the system with the plenum cover off to watch for leaks?

 

Yes, three times and let it sit about 5 mins before I started to put the intake top on. I guess I could take it off again and look, would have to get another gasket.

I had a gm car, 2.3l 95 year model that did this same exact thing when the fuel pump was bad, car acted the same way.. bad idle, long cranking sometimes, drove down the road almost normally, eventually died on me and wouldnt start.

 

The reason I say that it sounds like a rich condition (leak inside the engine) in the engine is because it starts up fine after sitting for a good long while. The fuel evaporates over time. A low pressure situation should exhibit starting problems all of the time, regardless of whether the motor is cold or hot.

You can run with the assumption that the pump is bad if you are sure that there is nothing going on in the plenum. I like to be sure before making someone pay for something that might not have been necessary and that includes the folks I help online.

 

I agree with K. Classic plenum leak symptoms.
Here's the question.. What do you mean 'apply some throttle'? If you mean 'pump' the accel, then vcm sends more fuel when it sees that.
Holding accel to floor causes vcm to shorten inj pulse thus minimum fuel. If it's flooding then in the prime testing situation, floor the accel, if it starts easier then.. it's flooding the plenum.

 

I guess the way I read that 'give it some throttle' line as that he was holding the throttle at some position and not necessarily at WOT or pumping the throttle. Definitely worth further explanation!