95 Jimmy 4.3 Vortec starting problems - weird

wb8yjf · 06-06-2006, 03:01 PM

This problem has been coming and going. Sometimes it will fire right up & runs fine. Other times you have to crank it ahile and it will fire up slowly, then runs fine. Last night wouldn't fire a lick. Put a charger on the battery (ran it down), tried again today - nothing. This I have do so far: New fuel pump/filter/lines/ ,new wires, new plugs, replaced the EGR Checked all connections (vacuum/electrical). I sprayed a llittle starting fluid in, it fired and ran fine. Engine has less than 70K miles on it (original lost a oil line and *BAM* 3 thrown rods....). I'm stumped. Any suggestions?
TY in advance...
Jon

rlith · 06-07-2006, 05:50 AM

Pull your upper plenum and check for washing... Run a can of seafoam through the system.

wb8yjf · 06-07-2006, 10:26 AM

Thanks for the info! There isn't anything "tricky" about removing the plenum is there? I haven't done that before. On the original engine that blew up, I saw the inside of the plenum and it was washed due to the injector spider assy. leaking, so I know what that looks like....

batkoach · 06-07-2006, 10:21 PM

you could also have a concern with the fuel pump relay intermittently not working . thy turning the key on first and listen for the pump to run before cranking . it sould run for 3 seconds then stop if comnputer does not see a crank signal. if no pump running and long crank time then starts the pump may be coming on after the oil pressure uint see pressure which will connect the fuel pump circuit on most cars and truck gm makes . this may explain the long crank time. how ever i do not have my schematic in front of me to be sure on your truck. check your fuel pump wiring schematic to be sure. i beleive once the computer sees pressure from the oil sender it turns off the relay.

jdmccright · 06-08-2006, 09:18 AM

Getting the plenum off isn't hard, just tedious with all the other stuff you have to unbolt first. I had a similar hard-starting problem on my '96 and it ended up being the fuel pressure regulator which is right in there on the back side of the injector assembly. Measure your fuel pressure...if it's below 57psi, change the regulator. Hope this helps!

wb8yjf · 06-08-2006, 09:29 AM

Thanks for all the info guys! I don't think it is the fuel pump or the relay because it will run once it fires up...I'll double check all of that though. I'll take the plenum off and give it a good eyeballing. I was wondering about the regulator... It kind of acts like it isn't getting enough pressure to send gas thru the injectors..? One thing that has me baffled is if the regulator was bad, once it fires would this some how overcome that problem and send gas to the injectors? I sure miss the old days of a carburator... a lot easier to figure out.

Thanks again guys!
Jon

wb8yjf · 06-12-2006, 08:27 PM

I'm getting a regulator & a 10mm deep socket (I have ever one but the friggin 10mm) tonight and tearing into this tomorrow. This place rocks! I just hope THAT IS the problem, but from all the links posted by Blazee it sure sounds like it. I will post results and findings.

Thanks again!
Jon

wb8yjf · 06-14-2006, 12:12 AM

OK, I changed the regulator AND found a bad vacuum line going to the intake manifold. Inside the plenum didn't look like it was washed out anywhere. BTW, THANKS for the thread on replaciing the regulator!!! That made this job a helluva lot easier!

I also replaced the PCV valve, just for good measure. I fired it up & it fired! I drove it tonight and fired it up 3 or 4 times w/o any real problems, then the last time I tried it, it was acting wierd again. Crank about 4-5 times, turn the key off, and crank again - this time it fired up & I made it home. During the drive, it acted a lil hesitant at times, but idled fine. Does this sound like some sort of sensor? Here is what I have replced:

Fuel pump
Lines to fuel pump
Sensing unit (pump assy)
fuel filter
regulator
EGR valve
cap/rotor/wires
plugs (all but #3 - I;m working on it!) and all but 1 looked pretty good & it was only a lil fouled

I'm stumped. Any ideas? Do any of you guys know how to test the sensors?

Lost in ohio...

Tnx!
Jon

dpollard · 06-14-2006, 03:10 PM

I can point you in the right direction for the #3 plug. You'll find several ways in other posts. My preference is to move the intermediate steering shaft aside.
Briefy as follows-
wheels straight, steering lock off. Unsnap the black plastic cover where the shaft connects to the steering box, remove the bolt (11mm), telescope the steering shaft in and angle it out of the way.

Other ways I've read include 1- accessing through the fender wheel with proper combination of wrenches, 2-or using a suitably angled box wrench directly on the plug base to loosen, then use your fingers.

I am curious to see what you find with the starting issues as my 95 is developing starting issues now. I haven't gone through all the commons items yet.

batkoach · 06-14-2006, 06:03 PM

remember in my earlier post about the fuel pump relaymay be intermittently not working which would cause long crank time till the oil sender see's pressure it turns on the fuel pump power circuit. locate fuel pump relay and have test light or multimeter reading wnd when con ern happens to test if relay is sending power to and if not don't forget to check the primary side of relay to make sure it is getting signal to turn on relay. remember to use wiring schematic to chack the correct circuits. please post results, john

batkoach · 06-14-2006, 06:05 PM

excuse above post for not useing spell check

wb8yjf · 06-15-2006, 07:07 PM

OK here is where I'm at. I took my truck to a big garage (city) and had a friend hook up a bazillion dollar scanner to the computer. NO codes, none whatsoever. I'm still having to spray starting fluid in to get it running. IAlthough the battery seems OK, I'm replacing it.I am (almost) completely convinced that this is the problem. I just can't find anything wrong or anything bad. If this fixes it, I am gonna have this stored in memory FOREVER. I talked to probably 10 mechanics who grilled me over this, and they are buffaloed too. Only thing left is the friggin battery.Every question they asked was answered with a "I did that". It runs fine once started...so it HAS to be the battery, right? I'll post tomorrow once I have that done.

I just want to thank EVERYONE on this board who have helped me on this problem. I'm a LOT more familiar (although I don't know if thats good

) with this 4.3 Vortec now. I'm gaining some confidence.

God, PLEASE let it be the battery...otherwise I'm completely lost.

Thanks guys....
Jon

blazee · 06-15-2006, 07:18 PM

Quote:

Originally Posted by wb8yjf

OK here is where I'm at. I took my truck to a big garage (city) and had a friend hook up a bazillion dollar scanner to the computer. NO codes, none whatsoever. I'm still having to spray starting fluid in to get it running. IAlthough the battery seems OK, I'm replacing it.I am (almost) completely convinced that this is the problem. I just can't find anything wrong or anything bad. If this fixes it, I am gonna have this stored in memory FOREVER. I talked to probably 10 mechanics who grilled me over this, and they are buffaloed too. Only thing left is the friggin battery.Every question they asked was answered with a "I did that". It runs fine once started...so it HAS to be the battery, right? I'll post tomorrow once I have that done.

I just want to thank EVERYONE on this board who have helped me on this problem. I'm a LOT more familiar (although I don't know if thats good

) with this 4.3 Vortec now. I'm gaining some confidence.

God, PLEASE let it be the battery...otherwise I'm completely lost.

Thanks guys....
Jon

Your problems are consistant with a low fuel pressure condition. You need a minimum of 60 psi for trouble free operation. 54 - 60 PSI will normally cause hard starting. Below 54 will usually only start with staring fluid. Below 43 PSI and the engine will not run at all.

Low fuel pressure at startup can be caused by several things. A weak battery, a weak fuel pump, clogged fuel filter, leaking nut kit, and/or leaking regulator.

If you didn't see any signs of leaking when you had the plenum off, then you can probably eliminate the regulator and nut kit.

This leaves the battery, fuel pump, and/or fuel filter. Just because the fuel pump and filter are relatively new doesn't mean that they should be over looked. A fuel pressure test with the key on and engine off should help trace which is the problem.

Here's another thread where the problem ended up being the battery, There's also a short explaination as to why it causes a hard start:
http://www.automotiveforums.com/vbul...d.php?t=568768

wb8yjf · 06-17-2006, 12:43 PM

Well, the new battery didn't fix it. I am borrowing a fuel pressure test guage today and am gonna check the pressure. I hope it isn't the new OEM pump in the tank....I also ran some Seafoam thru the gas just for the heck of it. I'll post the results of the pressure test. I HAVE to be getting close....

Thanks again!

Jon

wb8yjf · 06-17-2006, 07:05 PM

I went to my buddies house today and stuck a fuel pressure guage on it - now here is a potential problem - we dropped tha damn thing several times & broke the plxiglass front to the meter (kept falling off the inside of the hood), so not sure this thing is still accurate. I turned the key on & it jumped to 60 PSI right away, then dropped to about 20 PSI. We tried this several times, and basically the same thing. I can start it only after letting the pump cycle then shut off. After that, maybe a lil slow, it fires and runs fine. I plan on getting a fuel pressure gusage of my own & re-checking. My question is, if the pressure really dropped to 20 PSI, would it even run at all? I'm starting to think nut kit. When I had the intake manifold off, I didn't see any real signs of washing, except that area was a little cleaner than the rest of the manifold. This engine has less than 50K miles on it, so maybe this untrained eye wouldn't catch it? On a scale of 1-10 on the amount of carbon & varnish on the manifold, I would say this area was about 1 cleaner than the rest of the manifold. Nothing like the last engine where the drivers side was shiny clean & the passenger side was about a 7. I'm pretty confident with taking the intake off now. Should I try the nut kit? Would there be any other indications this was leaking?

Whew...

Thanks again!
Jon

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