1994 Jimmy

[s15jimmy]

I have a 1994 Jimmy with 4.3 Vortec and around 182k. Broke down on me the other night and has been no-start ever since unless it gets starting fluid. It will run and stay running, but idles rough like its leaning out on gas or air idle control is bad. I have read that this indicates the sending unit at the fuel pump. My question is if it does not hold pressure (readings were 48-55 when tested) what does this indicate? It doesnt take long for the pressure to leak off...basically it does not hold.

How big of a pain is the sending unit to replace and should I go ahead and replace the fuel pump with it? Is this actually the problem? Seems like it would make sense to take care of two birds with one stone..drop the tank once and done. Any insight would appreciated. I have replaced the electronic pickup in distributor, rotor button, distributor cap, plugs, and ignition control module. It cranks healthy, but no fire. Help!

 

[Molson02536]

I have a 1994 Jimmy with 4.3 Vortec and around 182k. Broke down on me the other night and has been no-start ever since unless it gets starting fluid. It will run and stay running, but idles rough like its leaning out on gas or air idle control is bad. I have read that this indicates the sending unit at the fuel pump. My question is if it does not hold pressure (readings were 48-55 when tested) what does this indicate? It doesnt take long for the pressure to leak off...basically it does not hold.

How big of a pain is the sending unit to replace and should I go ahead and replace the fuel pump with it? Is this actually the problem? Seems like it would make sense to take care of two birds with one stone..drop the tank once and done. Any insight would appreciated. I have replaced the electronic pickup in distributor, rotor button, distributor cap, plugs, and ignition control module. It cranks healthy, but no fire. Help!

If you don't have any check engine light while the engine is running, then 95% its going to be your sending unit. The fuel pressure to get the engine to start should be 62-65 PSI then drop around 5 psi when the engine is running.

Before you drop the gas tank and replace the fuel sending unit, inspect your ground wire from the sending unit. A bad ground will cause your fuel pump to be weak, just follow the wire harness from the top of the tank and you'll see the ground wire where it's grounded to the frame.

Common for the ground wire to corrode and take not that there is a good chance also that your going to have to replace the gas tank when you replace the fuel sending unit. Good news it, the tanks are not the expensive.

Keep us posted

Molson02536

 

[s15jimmy]

Molson, thanks so much for replying!

Here's the story so far for this evening: replaced fuel pressure regulator and still no start. Still will run on carb cleaner and stay running, but now its missing whereas it was running smoothly with the exception of it going lean on fuel. Hubby is at wits end with it and threatening to send to scrap heap. My uncle took the ground wire and put it directly on a clean engine ground and still the same result...just FYI.

Im wanting to try the sending unit with a new fuel filter and see what that does. I hate to keep throwing parts at a vehicle this age with as many miles as it does. I know there is still life in it. Just feel kinda stupid that we havent solved the problem yet...just seems like it would be something so simple. Never had a problem such as this. Sooo frustrating!!! Just did an oil change and plug change last weekend. The plugs on the left bank (2 ,4, 6) were black while the other three were normal. Maybe that is a clue to something...but that is the reason why we replaced the pressure regulator. If you still think its the sending unit, please let me know.

 

[s15jimmy]

Progress...

So today, progress was made. Yesterday, after changing the fuel filter it managed to start and run on its own. So today, the fuel pump was changed (which turned out to be bad) but still had a rough idle problem. It would start on its own but would overload and choke out. Let it sit for a few minutes and try to restart, same thing..starts and runs for a few minutes but chokes out. Uncle hooked his computer to it and it showed that the ECU was bad, so replaced it today as well. It starts and runs, but I know that the ECU has to learn the fuel curve, etc. but Ive read in a couple places about a relearn procedure. Does anybody have any idea what this is and if it can be done in the driveway or does it have to hit the shop?

So far, this is what has been replaced: fuel pump (Delphi), fuel filter, fuel regulator, upper to lower plenum gasket, electronic pickup in distributor, distributor cap, rotor button, ignition control module, spark plugs x2 (last time with AC Delco), wires, and now the ECU. Is there something I am missing?? or does it just need the relearn thing? Im happy to have it running (a few hundred bucks later), just want to get it fine tuned.

 

[Molson02536]

So today, progress was made. Yesterday, after changing the fuel filter it managed to start and run on its own. So today, the fuel pump was changed (which turned out to be bad) but still had a rough idle problem. It would start on its own but would overload and choke out. Let it sit for a few minutes and try to restart, same thing..starts and runs for a few minutes but chokes out. Uncle hooked his computer to it and it showed that the ECU was bad, so replaced it today as well. It starts and runs, but I know that the ECU has to learn the fuel curve, etc. but Ive read in a couple places about a relearn procedure. Does anybody have any idea what this is and if it can be done in the driveway or does it have to hit the shop?

So far, this is what has been replaced: fuel pump (Delphi), fuel filter, fuel regulator, upper to lower plenum gasket, electronic pickup in distributor, distributor cap, rotor button, ignition control module, spark plugs x2 (last time with AC Delco), wires, and now the ECU. Is there something I am missing?? or does it just need the relearn thing? Im happy to have it running (a few hundred bucks later), just want to get it fine tuned.

Sorry i was out on tour this weekend and had no time to log on. Recheck your timing and set it if its off.

When using a timing light connect an adapter between the No. 1 spark plug and the No. 1 spark plug cable, or use an inductive type pickup. Do NOT pierce the spark plug cable. Once the insulation of the spark plug cable has been broken, voltage will jump to the nearest ground, and the spark plug will not fire properly.

On the V6 engine, the system will go into bypass mode by disconnecting the timing connector. This is a single wire sealed connector that has a tan with black stripe lead. On the 4.3L engine, this connector is in the cab where the Heater Box and the carpet meet on the passenger side floor.

The timing specifications for the 4.3L engine is 0°TDC.

Set timing under the following conditions:

Normal operating temperature.
Air cleaner installed.
A/C "OFF".
Transmission in neutral.
Disconnect SET TIMING connector (tan/black wire) located in the cab where the Heater Box and the carpet meet on the passenger side floor. DO NOT disconnect 4 wire connector at distributor.
Connect timing light and adjust as necessary by loosening hold down bolt and rotating distributor. For specification, refer to SPECIFICATIONS/TIMING MARKS (0 TDC). Tighten hold down and recheck the timing. Stop the engine and connect SET TIMING connector. Clear control module trouble code by disconnecting control module power source or use bidirectional scanner.

Keep us posted

Molson02536

 

[s15jimmy]

Ok, giving an update.

Drove it yesterday and overall it did well. It idles rough at stop lights/signs and sometimes is rough taking off from a light/sign (runs rough). Today, however, was a different story. If just cruising along around 50 or so MPH, its fine. But step on fuel to get it along and it shudders..like its not getting enough fuel or timing is off.

I am going to try the timing trick. Its the only thing left basically to look at. We have replaced about everything having to do with air/spark/gas and ECM was installed on Saturday. At this point, just saying go or blow since Im so frustrated with not being able to completely figure this thing out.

 

[s15jimmy]

So giving another update. Thought there may have been a problem with the ECU, but didnt even get around to figuring that out. It hydrolocked and uncle and hubby are in the process of fixing the issue. The injection spider apparently went bad. Still dont know if there is something up with the ECU but will get around to that. Will keep giving updates as things progress.