****PLEASE DO NOT HIJACK THIS THREAD*****

Hello, I'm new to this forum but want to contribute with my problem scenario which I cannot find a solution. I have found this very same problem numerous times on this and other forums. But as in every other post, I see a bunch of suggestions, continuous part change outs and finally an open ended unanswered problem that still exists. If someone knows the answer, then point it out immediately. If you have comments or suggestions, please add value. But, by no means, DO NOT HIJACK THIS THREAD WITH YOUR OWN PROBLEM. I want to solve this problem once and for all and see if this thread will be useful to someone else in the future. I will edit this first post as I fine tune this issue and the tests that I do so be aware in advance.

My vehicle:
1999 LS Blazer, 4.3L, Vin W, 2WD, 4 Door, Automatic, 125,000 miles.

My problem scenarios:
1. After engine is warmed up pretty well at least 30-60 minutes, Blazer has intermittent stalling and eventually dies. There are no error codes.
2. This is a gradual problem that is first noticed with a lack of power that builds up.
3. As the gas pedal is applied further, the vehicle tends to lose more power and ultimately just dies.
4. At restart, the vehicle can go about 300 feet and the cycle happens again.
5. At restart, if it is left in PARK, the vehicle just sits there idling fine but eventually sputters and dies.
6. This tends to occur when it is hot outside. Let's say over 95-100 degrees.
7. After the engine is allowed to cool off, it can be driven again for a good 30-60 minutes and then it happens all over again.
8. When this situation is happening and the motor is still running, the oil pressure gauge is hovering around 30 psi, Otherwise, it is up around 40-45 psi.
9. Engine temp is around 195 degrees, never goes above that.
10. Coolant level is full and does not leak.
11. One time on a long trip after a fill up, I did smell gas fumes for a little. I had just filled up so this may be what I was smelling. Not sure.
12. Also, notice a "sweet" smell coming from exhaust. I have this same smell from my Ford F150 so when I smelled it from the Blazer it caught my attention.
13. I hear an intermittent purring, it's hard to describe. It sounds like a heat shield light vibration. Kinda like the way a brake rotor dust shield sounds when its loose. This is not something that is continuous and it seems to be coming from the fuel tank area, left rear side of vehicle. Exhaust is on the right side.

Points to mention:
1. This motor is a swap into my Blazer since the original one had broken a rod from coolant leak. I bought it that way and I did the engine swap.
2. All the following are new parts from the swap:
- Intake upper & lower, manifold gaskets.
- Coolant, green. Why, because I don't like doing intake gasket repairs and I hate changing engines. Research this and you'll know why.
- Positive Crankcase Vent. Valve (PCV)
- Ignition Control Module (ICM), because I wanted new
- Ignition Coil, because I wanted new
- Mass Airflow (MAF) Sensor, because I wanted new
- Oil Pressure Sensor, because engine was out and it's a pain to change
- Oil Pump, because engine was out and it's a pain to change
- Knock Sensor, because engine was out and it's a pain to change
- Coolant Temp Sensor, because engine was out and it's a pain to change
- Distributor, cap, rotor, wires, plugs
- 195 degree thermostat
- Battery
- Air filter
- Fuel filter
- Fuel Pump Relay, OEM GM part
- Gas Tank Cap, OEM GM part
- 10-30W Oil
3. MOD: Throttle body mod, removed diffuser/restrictor off bottom of blade

Tests that I have done so far:
1. Drove vehicle on highway/city at night for 60 minutes at 85 degrees outside and the problem does not occur.

2. Fuel pressure tests:
Fuel Test #1: Engine cold, conditions at 7 pm, 85 degrees outside temp, gas tank 1/2 full, no rain:
- 65 psi at ignition on, engine off, fuel pump primes
- 58 psi at start up and idle
- 65 psi at accelerate
Fuel Test #2: Engine cold, first start of the day, conditions at 12 pm noon, 88 degrees outside temp, gas tank 1/2 full. no rain:
- 65 psi at ignition on, engine off, fuel pump primes
- 58 psi at start up and idle
- 65 psi at accelerate
This happens for all tests upon engine turn off:
- Pressure goes back to 65 psi as fuel pump runs for 2 seconds.
- When pump shuts off, fuel pressure comes back down to 58 psi, holds for a few seconds.
- In the next 15 seconds, pressure goes back to 65 psi
- Pressure is 60 psi after 10 min
- Pressure is 60 psi after 20 min
- Pressure is 58 psi after 30 min

3. Oil pressure test:
- Can't remember the number but it was in spec.
4. Fuel injector connector test with noid light and all signals were there.
5. Fuel injector fuel test, all injectors were squirting fuel out.
6. Engine compression test, all cylinders check to be 130-134 psi.
7. Catalytic converter pressure test done by muffler shop, before and after cat and muffler, no high pressure buildup. They check good.

Tests to do:
1. Fuel pressure test in heat of day
2. Fuel pressure regulator
3. MAF
4. Vacuum leak around air intake
5. EVAP system
6. TPS
7. EGR
8. Gas tank pressure vent clogging or fuel return line clogging
9. ICM
10. Whatever it takes to fix this permanently!


Keyword phrases:
blazer stumbles sputters when accelerator pushed hard, no error codes, stalls on hills, fuel pump whines when hot, stalls when hot outside, fuel pump making loud howling noise, buzzing noise under car, clogged cats catalytic converter, fuel pressure regulator, fuel pump pressure test, sweet smell from exhaust, charcoal canister, evap canister, ICM overheat

 

gosh my 88 ford mustang did same thing, sure enough the fuel filter was plugged the mechanic couldn't even blow threw it. pump got hot and after I changed filter it worked for several years no problem.


try fuel pressure test cold engine, not running. hold for 3 seconds. then write down spec


then wait 10 min, write down spec




leave not running

 

My fuel filter is new. I did all those pressure tests when I first installed the engine before I had this problem. The fuel pressure regulator was okay.

 

Post #1 has been edited.

Also, I am not convinced the fuel gauge is working right. Maybe someone can chime in on this one. It seems to consistently go down to 1/2 tank after I've driven only 100 miles.

When the "Low Fuel" light comes on and I fill it up, 12 gallons is the amount that I need to fill it up. So based on the fact that I have an 18 gallon tank (4 Door tank size), there are roughly 5-6 gallons left in the tank. Is that what you guys are seeing for yours?

One more thing to mention. I'm getting around 18-20 mpg on highway. I recently did a big trip before I had this problem. So that means I should be getting around 324 - 360 miles per tank. Is that what you guys see?

 

i never run mine down that low, these pumps are more likely to go. rule of thumb dont let it drop below half. the one time i did let it, the light came on and took 14-15 gallons so that sounds about right. sometime the sender unit gives you false readings and could have more than you think in there.

 

Could you please do a fuel pressure and leak down test so we can rule out the fuel system? Pressure should be 60-66 psi with the key on engine OFF. Pressure should hold above 55 psi for 10 minutes after the pump shuts off.

Do you have a scanner that can read live data?

I have seen this problem before and it was the ICM for those people. It gets very hot. You need to use an AC Delco brand and make sure it has thermal grease applied to transfer the heat from the back of the ICM. Check for spark the next time it stalls

 

I already did this, see my Post #1.

No.

One of my tests to do still.

 

I need to find out why. This isn't something that was designed this way.

 

Fuel Pressure Test #3: Engine hot, drove vehicle for 2 hours, highway/city driving, conditions at 2-4 pm, 95-99 degrees outside temp, gas tank 1/2 full, no rain:
- 65 psi at ignition on, engine off, fuel pump primes
- 58 psi at start up and idle
- 65 psi at accelerate

New situation to analyze with the following observations:

1. When gas tank gets low EXACTLY AT POINT WHEN "LOW FUEL" light comes on, the problem begins and my symptoms occur exactly as stated in Post #1.

2. Fuel pressure begins to do the following:
- 55 psi at idle
- 55 psi on normal driving
- 60 psi on normal acceleration
- 52 psi on hard acceleration and severe engine stall
NOTE: On all these readings, the fuel pressure gauge needle flutters, jitters, bounces. It does not stay in one place. Seems the readings are more of a range of pressures, for example: 55 psi is more like 55-58 psi. Like there is air or bubbles in the lines??? Could that be what is doing this? I can even hear it when I open the hood. The fuel gauge is on tight the fuel line Schrader valve so I don't think it is coming from that.

3. Speedo bounces intermittently when fully pressing the gas pedal. I will be cruising at 75 mph and then stomp on it and the Speedo bounces from 55 to 90 once or twice.

I pulled over and did the following:

1. Changed Fuel pressure relays, drove it again and still same situation. So I can rule out the Fuel pressure relay. I have the OEM GM one back in there.

2. I added 2 more gallons of gas back into the gas tank. GUESS WHAT? PROBLEM WENT AWAY.

3. I drove the vehicle again until the gas went down to low EXACTLY AT POINT WHEN "LOW FUEL" light comes on, AND GUESS WHAT?? THE PROBLEM CAME BACK AGAIN!!!

Now Einstein, what the heck does that mean?

Could it be?
1. Bad sending unit on the fuel pump, maybe shorting out the pump and keeping it from pumping fuel?
2. Bad electrical to the fuel pump?
3. Short somewhere?

Any ideas?

 

With the engine OFF do a fuel pressure test. not running.
turn key on, when the pump is running you get what?
when you turn the key off you get what?
NOW, leave the pressure gauge hooked up.. DO NOT start the truck, let it sit for at least ten minutes,,, what is the fuel pressure NOW??? did it drop below 55lbs???
as you can read in other posts, there is no engine running fuel pressure test.