95 BLAZER stalling-not starting. HELP!

[splitter6]

hello to all, i am new to this forum and this is my first post. after surfing the web for a while this site seems like the best.
i have a 1995 s-10 blazer LT 4.3 vortec vin W.
i've had many mysterious problems with it that are hard to pinpoint because like magic the truck sometimes idles rough then starts running ok and then just quits in mid drive. sometimes starts again sometimes won't.
over the last week i've found that it will turn over if i spray choke cleaner in the plenum either through the air intake or the top.it usually won't stay running though. this leads me to believe that there is no fuel getting there in the first place. i can hear the fuel pump kick in on every start attempt. everthing seems to be ok because she sometimes fires up and runs ok for a while (5 seconds to 5 days)
i have had some work done on it (cpi unit, ignition coil, egr valve cleaned,fuel filter,pressure test, alternater) i've had it to mechanics and get what i can done myself with the help of these forums. but now i hope i can rule out a few things with help from you guys (or girls).

[Jeremy Fitch]

Before really trying to pinpoint anything you need to check the fuel pressure. Trying to do anything before that would be jumping the gun. Try to get the pressure tested at the test port and we can go from there. You can get a tester at Auto Zone for free, only have to pay deposit.

[splitter6]

the mechanic i brought it to at the start of all this said he did a pressure test and it was ok. i think he said it was 58 psi.
is it possible that it may test ok and then go bad.
i say that because the engine runs good only sometimes. would i have to test it only when it is running poor or not at all to get an actual read?

[Jeremy Fitch]

Originally Posted by splitter6

the mechanic i brought it to at the start of all this said he did a pressure test and it was ok. i think he said it was 58 psi.
is it possible that it may test ok and then go bad.
i say that because the engine runs good only sometimes. would i have to test it only when it is running poor or not at all to get an actual read?

Yes, I guess it is possible. Will probably be a very hard problem to pinpoint because of the come and go nature of it. But I would definetly try to get it pressure tested a few more times, especally when its running bad.

[Cailen]

58 is low fyi. You want to be between 60 and 64, preferably closer to 64.

I would recommend checking this thread first:
http://www.automotiveforums.com/vbul...d.php?t=453370

You never know, your problem could be as simple as a clogged fuel filter/air filter or a bad plug. Do yourself a favour if you haven't done one in the last little while and do a tune up, then start worrying about fuel pressure and such.

[splitter6]

yea, that's the thing... i have done sme of those things. the car starts and will run if fuel is sprayed into the throttle body at the air intake. so i gotta think that new plugs & an air filter probably are not a high priority problem. it's got to be fuel delivery that makles it stall and not start. it runs good and starts sometimes for days so the newer fuel filter can't be clogged.
i dunno...if 58 psi is low the i'm going to have it rechecked and try to do it when it's not startng too. (where is the fuel pressure test port anyway?) i'll let you know how it works out. thanks!

[Cailen]

Behind your intake manifold you have the inlet and return lines. The test port will have a black cap on it.

[rlith]

Originally Posted by Cailen

58 is low fyi. You want to be between 60 and 64, preferably closer to 64.

I would recommend checking this thread first:
http://www.automotiveforums.com/vbul...d.php?t=453370

You never know, your problem could be as simple as a clogged fuel filter/air filter or a bad plug. Do yourself a favour if you haven't done one in the last little while and do a tune up, then start worrying about fuel pressure and such.

Not really, CPI specs call for 56-60 at start and 61-64 at running... Neither one of us are sure about how is mechanic did the pressure test.

That said, I would pull the upper plenum and check for washing.. While testing fine for immediate pressure, you could still have a bad fpr on the CPI and causing fuel dump..(Same with a bad nut kit) If you can rule that out, I would start looking at the crank sensor and reluctor ring (rare for a reluctor to go bad, but I've seen it happen) If your 95 has the ECM in the engine compartment, ignore my statement about the crank and reluctor.

[splitter6]

ECM?

well, the blazer is starting and runnig fine for the moment. why, i don't know. i checke d the fuel pressure and it's at 58-59 psi with ignition in "on" position and it drops to about 55-56 while idling.
could this cause the problems?
the guy at the parts store said it sounds like a fuel relay problem.
i like this truck but i just never know when it's going to go on me. it seems to have an evil mind of it's own.

[splitter6]

back to the same problems...whatta ya think?

[Jeremy Fitch]

These are taken directly from my haynes manual..

Specs are:

TBI system - 9-13 psi, decrease 3-10 at idle.

MFI system - 41-47, decrease 3-10 at idle.

CMFI system - 58 - 64, decrease 3-10 at idle.

CSEFI system 55-61, decrease 3-10 at idle.

[blazes9395]

Sounds like you have a weak fuel pump that is cutting out intermitantly. What does the pressure hold at? It has to hold around 60, for it to start. I would go with Cailen's advice, a tune -up would be wise if it hasn't been done in awhile.

[Cailen]

Neither one of us are sure about how is mechanic did the pressure test.

lol good point.

splitter based on the fuel pressure test results you're showing it doesn't sound like your problem lies between your pump and the test port. I really would try doing a tune up bro. When's the last time your plugs/wires/cap/rotor were changed? How about air/fuel/pcv filters? Diff fluids?

Before you get to all that though you'll want to do what rlith said and have a look at your manifold. You don't necessarily need to pull the plenum but it's a good idea. If you'd prefer not to just remove the Vortec name plate and the IMTV valve that lies beneath it and get yourself one of those snake lights. It'll cost about the same as an upper plenum gasket.

[splitter6]

from the sounds of it i think my pressure is ok going by what jeremy fitch posted and that i have a cmfi or csefi system. i will follow that advice although some has been done already.
what do you mean by holding? is that what pressure would read after idling for 10 minutes or so? could it be a relay or a clogged return line? how do you know if a fuel pump is intermitantly bad? and what's an ecm?

thanks in advance for the help everyone.

[blazes9395]

You really can't just look at it and tell if it is bad. The pump can have a bad contact inside, and although it still works, would be weak, and every time it heats up because it simply cannot keep up, it will stop and you stall, it usually gets going again after it cools a little. What I mean by holding is hook up a fuel pressure guage at the rear shrader valve and turn the key to the on position. The pressure should jump up right away, up to 60 and HOLD there after the pump shuts off. IF the presssure jumps up there and as soon as the pump goes off, drops back down, or bleeds down, you have found a problem. This can be several things from fule pressure regulator, a leak in the lines(or lines inside the intake), the pulse valve located in the tank(common problem) or lastly the pressure valve located inside the fuel pump itself.

Here is a little information from a manufacturer of fuel pumps(among other things)
http://go.delphi.com/Del/attachments...lish_10589.pdf