95 Jimmy 4.3 Vortec starting problems - weird

[blazes9395]

Before you do the nut kit, take off the upper plenum, or upper intake. The pressure is too low for it to start, 20psi is too low. Like blaze mentioned, there could be several reasons why your getting the low drop in pressure. Going back to the upper intake, take it off and take a look whats going on under there. Get a helper and with the upper plenum off, get them to turn the key to the "on" position ONLY, don't start it, just to the on position. As the key is turned, watch for leaks, if the nut kit/lines are leaking, you will see it. Either way if you see washing, you know you have an injector system problem.

[jdmccright]

If the gauge is still functional, then the initial 60 psi reading means a good fuel pump. A subsequent loss in pressure could mean a leak in the system somewhere, an incorrectly installed or bad regulator, or nut kit (BTW, what exactly IS a nut kit?). First, try the gauge on another truck to see if it's good. If so, then I'd suggest rechecking your install...something may have come loose or an o-ring isn't quite seated or cracked. We'll get to the bottom of this, or the bottom or your wallet!

[blazee]

As others have stated the pressure is too low. The high initial pressure that drops drastically would indicate a leak in the system. Most likely causes would be a leaking injector, regulator, nut kit, and/or pulsator. Personally, I would now check the pressure at the filter itself, this will let you know where the problem is. If the pressure still drops, then you know the problem is the tank, which would probably be the pulsator. In the pressure doesn't drop, then the problem is most likely in the plenum.

[wb8yjf]

OK, I might just have to do the remove the plenum thing. Evere since I deliberatly turn the ignition on & allow the pump to run for the initial pressure build up, I am getting it started every time. If I get in & turn the igintion on w/o allowing the pump to build initial pressure, it won't fire. I'm suspecting a small leak somewhere. It still runs fine if I just slow down the starting process a little bit.

I learned here that the nut kit is the set of lines that connect the fuel lines to the injector assy. It is under the intake plenum. They are 2 white hard (plastic?) lines. I saw one on ebay for about $90. I guess the best way to test them would be to remove the intake and do as described above by blazes9395. At least at this point, I'm not afraid of driving it!

[Megs1082]

Hey guys. My wife's 1993 Jimmy is having similar issues.

It developed over the course of a month or so from easy to start to hard to start. Now in order to get it to start you have to try for a couple minutes or hook it up to an external secondary car battery through jumper cables to get it to start.

I've replaced the plugs, checked the wires, changed the distributer cap, changed the fuel filter, and checked all the fluids before I really started getting concerned.

I bought a fuel pressure guage and hooked it up to the schrader valve. The pump hits 60ish and then - SOMETIMES drops off to below 50 and sometimes holds at 55. When the car is running it runs fine.

I've had the alternator, batter, and starter all checked out at autozone - they are all good. I would think this was a weak battery because of the fact that whenever I hook up a set of cables it will start in the first or second time. However - yesterday I swapped a 900 cranking amp battery from my Grand Prix into her Jimmy and put her 700 cranking amp battery in my Grand prix. The same problem stayed with the Jimmy even with the switched batteries. Now here's the odd part. Connect them via jumper cables and whalla ! instant start. The voltage doesn't change on the jimmy's guage when I connect the two? It just doesn't make sense.

After reading this thread it looks like it could be several things. The problem is that it seems very intermittent. The fuel pressure drops sometimes, doens't drop other times. The one key thing is that once it starts one time....It will start easily until it gets cold again - which makes me think it must be some sort of relay somewhere?????

I read in teh chilton's manual that the fuel pump relay may need to be changed. But I don't know where that is???? It says in the convieniece center in the middle of the dash but I see no such thing??? Any ideas? Things next to try - I don't know what much else to do here????

[wb8yjf]

If I remember correctly, the relay is inside the glovebox, behind a panel. When I get a chance, I'll get the manual out and verify that for you. How do the connections look to the battery and have you checked and cleaned the ground connection? I had a bad ground to the frame or chassis once that was a PITA.

Jon

[wb8yjf]

If I remember correctly, the relay is inside the glovebox, behind a panel. When I get a chance, I'll get the manual out and verify that for you. How do the connections look to the battery and have you checked and cleaned the ground connection? I had a bad ground to the frame or chassis once that was a PITA.

Jon

[Megs1082]

we couldn't find that fuel pump relay behind this panel, and I don't see a convieiniece center anywhere like the chiltons says????

Any ideas where this fuel pump relay resides?

[wb8yjf]

I just looked at my 95 and the relay is located in the panel in the glove box behine a panel marked "relay access" - the panel is on the drivers side of the box. There are 2 located there, small black relays. I did a google search on this and I saw several places that say the same thing. I replaced mine a few years ago when I had pump problems. Hope that helps.

[wb8yjf]

Oh yea, BTW the owners manual and my Hynes book don't list this. Why? I don't know what the big secret is....

[Megs1082]

My wife and I took apart the whole dash this morning only to find out they are in the engine compartment on the driver side front firewall. I even went to a dealership to ask where they were. Supposedly on the one we have it is on the drivers side wheel well according to the dealer - wasn't there.

According to our chiltons it was in the convienience center - wasn't there.

Sorta odd??? I bought a new one from autozone --will try this solution tonight.

[wb8yjf]

That IS weird. Is your Jimmy a 4X4? Maybe they did things differently?

[Megs1082]

it is a jimmy 4x4....

I still can't figure out the problem. Replaced teh Fuel pump relay - no change. It's getting worse I can't start it at all now practically.

I took of the intake air/fuel cylinder thing - and peeked inside. It did NOT smell gassy. I attempted to start the car as well as just turn the key to where the fuel pump went active, I could neither hear nor smell gas leaking. So I don't really think this is a fuel regulator or intake "area" problem.

Fuel pump the next bet?

[jdmccright]

I think the next possiblility would be the...get this it's so obvious...the Fuel Injector Cold Start Valve. Had to look it up and don't ask me where it is. Either it is stuck or a bad circuit. Needing a jump from a healthy battery might indicate an electrical issue or just that it needs the extra juice to get it to move.

[wb8yjf]

Jdm-
OH MAN...you mean there is YET another part to this engine I haven't heard about!? I haven't seen anything about a cold start valve on a '95 Jimmy....PLEASE tell me this isn't something I should replace! My book dosn't reference one ( a Haynes book)

Hey Megs, have you tried to get it to fire with a shot of starting fluid in the intake? When mine was practically DOA, that was the only way I could get it to fire. Give it a shot & let us know if it does fire & will run OK if it does... I'm feeling ur pain, BELIEVE me, I've been battling mine for over 6 weeks now - BUT It will start, stop, and all the lights work NOW!