Ok, as most of you guys know from the thread I started "'95 Jimmy 4.3 Vortec starting problems - weird" I have been fighting this for a LONG time. It all started out with a DOA fule pump.

Here is what I have done so far (as far as the engine)
Replaced:
Pump/strainer/sending unit (twisted lines), pulsator
fuel line (had a mechanic do that - I ain't that good at bending or routing lines)
Fuel filter
Regulator (on old injector assy)
Nut kit (return line has 2 leaks in it)
Injector assy ( #3 had a rub mark in it and I suspected a leak)

I get this all back together & I'm STILL having problems! It will start sometimes, others not - it will fire with starting fluid. It isn't idling smoothly at this time (next thing I'm gonna do is check the EGR).

I bought a fuel pressure guage today, hooked it up and here is what is weird...."sometimes" when I turn the ign. on (not starting it) the pressure guage will jump to about 55-60 PSI, then it drops to ZERO. If I crank it, the pressure will jump up and stay there BUT it will read either low or correctly (WTF?) I pulled the fuel pump relay out (it was HOT as was the one next to it - located in the glove box backside). I bench tested the relays & BOTH tested good (one is new (pump) and the other isn't new. I cleaned the pins on the relays & sprayed the connector with DeOxit D5 (this is REALLY good stuff) I swapped them - same result. Can this possibly be an ignition switch problem??? I just don't get it. If it is the ign. switch, why would it run once I juice it with starting fluid? I am a wits end...my electronic mind isn't comprehending this. NO fuel leaks, no smell of gas, no dripping gas, etc. Everything in the fuel delivery system is less than 2 months old.... :( ANY ideas? I don't want to buy a new vehicle - as this engine has less than 50K on it. I'm STUMPED....

BTW, I took it out today (after starting it with ether) and it ran like crap. The check engine light FINALYY came on, but when I got home & re-started it, the engine fired & the light went off b-4 I could see what the code was! :(

I'm trying my absolute best to keep this Jimmy on the road - but I am MIGHTY frustrated at this point! H E L P !!!

Tnx,
Jon

Yeah, you've been through the wringer. I saw a post on the '93 and they had a good suggestion. Hook up your fuel pressure gauge at the schrader valve. Find a portion of the fuel delivery line where it is rubber. Be ready with something to pinch it off (vise grip set just loose enough to hold it pinched off or other) and have a friend/significant other turn the key to on so that the fuel pump goes. As soon as it stops, clamp off the hose and watch the pressure gauge.
If it holds, then your problem lies aft of the clamp point (i.e. bad pump, pulsator or return line). If the pressure drops, then the problem is at the front end. Then after a couple minutes, when you release the pinch, if the fuel pressure at the guage drops really low it means the pump isn't holding pressure in the tank. I guess we're all stumped at this point...time to go back and check all you've done. (Thanks Megs1082 for the hint!)
The only other possibility might be the IAC valve, but check the pressure drop out first...that sounds like the major problem to tackle first.

I guess anything could be a problem at this point. I believe the only rubber part of the line is by the pump if memory serves right, but I'll give that a shot. Be MY luck, I'd pop a hole in it while pinching it....Jeez, EVERYTHING is NEW in the fuel delivery system - literally. REALLY grating my nerves at this point in time. I thought for sure it was the bad nut kit and/or the CPI, but nope. What I find is so weird is that the pressure drops to zero(??????), that sounds like a big leak, but no leaks. I suppose the new pump could be bad, but I doubt it... Believe me, when I finally figure this out, I'm posting the results!

Thanks!
Jon

I've never replaced a fuel pump (knock on wood!) but it could be as simple as a reversed check valve or a seal/O-ring that was damaged or defective while installing the new one. Could also be a partially disconnected pulsator. Good luck!

Here is what I have done so far (as far as the engine)
Replaced:
Pump/strainer/sending unit (twisted lines), pulsator
fuel line (had a mechanic do that - I ain't that good at bending or routing lines)
Fuel filter
Regulator (on old injector assy)
Nut kit (return line has 2 leaks in it)
Injector assy ( #3 had a rub mark in it and I suspected a leak)

I get this all back together & I'm STILL having problems! It will start sometimes, others not - it will fire with starting fluid.

I bought a fuel pressure guage today, hooked it up and here is what is weird...."sometimes" when I turn the ign. on (not starting it) the pressure guage will jump to about 55-60 PSI, then it drops to ZERO. If I crank it, the pressure will jump up and stay there BUT it will read either low or correctly (WTF?)
Tnx,
Jon


This is not right, what I bolded up top. As soon as you turn the key, it should jump up to the pressure and stay there, with the engine off.

If it is leaking down as soon as the pump stops priming, you will get a no start, or a hard start.

This can be the pump itself, the pumps internal valve, its designed to pressurize and HOLD the pressure once the pump stops working.

It could be the pulsator that could be leaking - very common, but I just seen you replaced that.

It could be a leak in the pressurized line going to the engine, on the sending unit, but inside the tank, so no leak outside.

And last but not least, it could be the regulator on the injector unit. I know you mentioned you replaced it, but it could be defective, seen it happen a few times, especially the ones that are just changed individually.

Since you mention it works sometimes and other time not, I would bet either a regulator problem, or a pump problem (defective).
Hope this gives you an idea.

This is not right, what I bolded up top. As soon as you turn the key, it should jump up to the pressure and stay there, with the engine off.

If it is leaking down as soon as the pump stops priming, you will get a no start, or a hard start.

This can be the pump itself, the pumps internal valve, its designed to pressurize and HOLD the pressure once the pump stops working.

It could be the pulsator that could be leaking - very common, but I just seen you replaced that.

It could be a leak in the pressurized line going to the engine, on the sending unit, but inside the tank, so no leak outside.

And last but not least, it could be the regulator on the injector unit. I know you mentioned you replaced it, but it could be defective, seen it happen a few times, especially the ones that are just changed individually.

Since you mention it works sometimes and other time not, I would bet either a regulator problem, or a pump problem (defective).
Hope this gives you an idea.

That is what I thought! I know a buddy who has a '93 and the pump held pressure...we looked at it again today & same thing. I was starting to thing something in the tank too. I just really hate to have to drop the tank (for the 4th time in 2 months!), but I guess I'll just have to bite the bullet & get 'er done. At least this time, I KNOW the lines will come off easily (I primered the lines & used anti-seise on the fittings THIS time). It is really bizzare, sometimes it will not build pressure, sometimes it builds the drops to 20 or so, sometimes it builds and drops to zero....I think I got me a lemon pump, pulsator, or line in the tank. I wasn't aware the pump had an internal valve in it! I sure sounds like that thing is "probably" the problem.... :(


Update: Today I had to use the car to go to a dentist appt. - started it with ether, drove there, started it with ether again & the check engine light FINALLY came on & threw an interesting group of codes...

Here is what they were:
#22 - Thottle body Sensor (low voltage)
#32 - Exhaust recovery system
#34 - MAP sensor (low voltage)
#54 - FUEL PUMP RELAY

New battery - I'm gonna go thru EVERYground I can find tomorrow! Wouldn't that just be the sh!t if it was a stinkin bad ground? I replaced the cable / ground connection off of the battery about a year ago....

I'll post back after I go through those grounds & hopefully this will be the mysterious culprit causing all this weirdness.....

Thanks for the input!

Jon

Ok, as most of you guys know from the thread I started "'95 Jimmy 4.3 Vortec starting problems - weird" I have been fighting this for a LONG time. It all started out with a DOA fule pump.

Here is what I have done so far (as far as the engine)
Replaced:
Pump/strainer/sending unit (twisted lines), pulsator
fuel line (had a mechanic do that - I ain't that good at bending or routing lines)
Fuel filter
Regulator (on old injector assy)
Nut kit (return line has 2 leaks in it)
Injector assy ( #3 had a rub mark in it and I suspected a leak)

I get this all back together & I'm STILL having problems! It will start sometimes, others not - it will fire with starting fluid. It isn't idling smoothly at this time (next thing I'm gonna do is check the EGR).

I bought a fuel pressure guage today, hooked it up and here is what is weird...."sometimes" when I turn the ign. on (not starting it) the pressure guage will jump to about 55-60 PSI, then it drops to ZERO. If I crank it, the pressure will jump up and stay there BUT it will read either low or correctly (WTF?) I pulled the fuel pump relay out (it was HOT as was the one next to it - located in the glove box backside). I bench tested the relays & BOTH tested good (one is new (pump) and the other isn't new. I cleaned the pins on the relays & sprayed the connector with DeOxit D5 (this is REALLY good stuff) I swapped them - same result. Can this possibly be an ignition switch problem??? I just don't get it. If it is the ign. switch, why would it run once I juice it with starting fluid? I am a wits end...my electronic mind isn't comprehending this. NO fuel leaks, no smell of gas, no dripping gas, etc. Everything in the fuel delivery system is less than 2 months old.... :( ANY ideas? I don't want to buy a new vehicle - as this engine has less than 50K on it. I'm STUMPED....

BTW, I took it out today (after starting it with ether) and it ran like crap. The check engine light FINALYY came on, but when I got home & re-started it, the engine fired & the light went off b-4 I could see what the code was! :(

I'm trying my absolute best to keep this Jimmy on the road - but I am MIGHTY frustrated at this point! H E L P !!!

Tnx,
Jon

be very careful with starting fluid, it will waste your valves and pistons, as the nmain ingredient in staring fluid is either, and will make any engine run for a short time. also , blow back can start a nice fire!!! good luck.:icon16:

I use it sparingly. Lately only using it to get it started when I have to run an errand or get beer :) Use the wifes truck in the mean time....

hey dude i see your problem has not gone away. at this point keep it simple. pinch off the return line and if this is a 4 wheel drive there should be 2 rubber sections by the trans/ transfercase, that is easier to get to to pinch off. making sure you pinched off the return line and have your gauge hooked up turn key on and if you get 55-60 PSI and it drops right away and there is no leak in the intake then you have eliminated the regulator as the concern and if you check a few plugs and they are not wet then the injector is probably ok . now you say you have no external leaks, then the only thing left is the pulsator or the pump. personally i have seen alot of new pumps go bad in a short time. try a bosch and airtex, they are better qaulity. also if you take the tank out to inspect the steel lines in the sender assembly for leaks and do not find one replace the pump and get rid of that pulsator and replace it with a rubber hose and to hose clamps. thats what we do in the shop and never had one come back with a problem and most fuel pumps come with a replacement hose instead of a pulsator. thanks for listening, john

It has been a LONG time since I posted on this subject, I gave up. I got really tired of crawling up under the Jimmy in the gavel driveway and dropping the tank! I've been using either the wifes truck or a buddys Jimmy (I'm posting a problem with THAT one next), and finally took it to a buddys shop. He has a lift, I don't.... Bottom line the problem was a BAD PULSATOR! Brand new, it was leaking like sieve & pressure dropped almost immediatly. I knew it would turn out to be either that or the pump, but honestly too busy with my business & gave up. He replaced it with a piece of rubber line & said is is runng FINE now! FINALLY!!!!

I'm not too sure how imporatant POS pulsator is, but by-passing it with a rubber line sure sounds a lot less exspensive and if I had done that from the get go, I wouldn't have had all these headaches.

Just wanted this forum know what the problem was. I guess one good thing about all of this (NOT all the $$$ I spent), is that I know a helluva lot more about this engine then I ever did & learned a lot from this forum. I found a leaking nut kit and an injector line while chasing all of this, so I should be go to go now! Practically a new engine.

Thanks for ALL of the suggestions and expertise on this!!!

Cheers,
Jon

From what I've seen and read, that is a common thing to do when the pulsator craps out. There are no ill effects and it will never fail on you again. Thanks for posting the solution!

Very welcome! That problem lasted me about 3 months or so & I just got tired of crawling under it & dropping the tank (almost full, OF COURSE). I'd hate for someone else to go thru this!