Fiero V6 Fuel Injected Engine Problems (Page 1/3)
altownsend MAY 27, 10:40 AM
I purchased a replica project with a 1986 Fiero base.

1986 Fiero, V6 Fuel Injected,4 Speed Manual

The fuel tank has fresh gas, new fuel filter, no visible or obvious vacuum leaks detected. Recently did a standard tune-up (Plugs, wires, distributor cap, rotor, sensors - temperature, idle speed). Alternator charging at 13.3 to 13.8 volts. Right now, the engine does not seem to be misfiring. Battery is new.

The engine starts after a few turns. It will hold idle until about the time that it gets up to Normal Operating Temperature. the idle will drop at Normal Operating Temperature, and it will eventually stall out. I have checked the fuel pressure, and it remained the same through this cycle. If the engine runs long enough, it gets hot enough for the fan to activate, and the fan turns off when the temperature drops.

However, the problem is that the engine will not remain at idle. It will stall out. There was a recent time (2019) that it ran until I turned the ignition off. But, now, it stalls out at idle.

Is there a Fiero V6 expert/tech person here that can spend some time with me to figure out what the problem is? I am in Houston Texas.
Spoon MAY 28, 09:47 PM
Right after it stalls out can you restart it easily without pressing on the gas? Did you apply a fresh layer of thermo paste under the ignition module?
What is your normal idle rpm? Does it stall out while driving down the road or only when your foot is off the gas pedal?
Have you checked the IAC valve on the throttle body for carbon fouling.
Does it stall out with rpms gradually getting lower & lower Or does it try to save itself with a See-Saw type idle?

Check EGR pipe between intake manifold and EGR valve. It usually has a heat insulating wrap around it so its hard to see. May have to remove the tube to be sure, 2 bolts /2 nuts.
Another vac leak source is a short rubber hose (with 90 degree bend) hidden behind the throttle body. connecting it to the intake manifold.

Check for proper grounding. Replace broken or missing ground straps. Engine block to frame, body to frame and chassis , etc. Can also check with a cheap Harbor Freight meter set to ohms.

I'm no expert but they should be along shortly...

Spoon


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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

altownsend MAY 29, 01:03 AM

Spoon,

Thank you for the questions. You brought to surface some new information for me to consider. Thanks for that. My response to your questions is below:

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Right after it stalls out can you restart it easily without pressing on the gas?

- I can restart the engine after it stalls, but it stalls again right away. However, if I feather the gas pedal, it will run again, but roughly, and it will not run smoothly again until the next time that I do a cold start again.

Did you apply a fresh layer of thermo paste under the ignition module?

-No, I did not install a layer of thermo paste under the ignition module. Please tell me more about that, and I will make the adjustment to say 'Yes" next time.

What is your normal idle rpm?

- Normal idle is about 1,000 RPM or so, maybe just under 1,000 RPM

Does it stall out while driving down the road or only when your foot is off the gas pedal?

- I purchased this project from someone whom purchased it from someone whom purchased it from someone (I am the 7th owner of the project) It has never, to my knowledge been on the street as a driver. So, from time to time, I start the engine to use up the fuel, so that I can put fresh gas in the tank. Lately, the engine has not ran for very long with the idle issue

By the way, I have fresh oil with new filter, new fuel filter, new sensors (including IAC)

Now, with what I just said, I have experienced the engine running until I got bored and turned the engine off, hence the engine ran until I decided to turned it off. Now, that was also when I had the idle air control sensor off. I have had this idle problem all along. Research suggested that I replace the idle air control sensor (IAC) located on the throttle body. With it off, the engine will run until it runs out of fuel or I turn the engine off. With the sensor off, the engine starts, idles without fluctuating, and has no issues. Now that we are discussing this, I will remove the new sensor again and see if the engine will run as 'normal'.

Have you checked the IAC valve on the throttle body for carbon fouling.

-Yes, I replaced it. With it off, the engine runs fine. With it installed, the engine will start and run fine until the engine gets up to normal operating temperature, and then the engine will reduce idle and eventually quickly stall.

Does it stall out with rpms gradually getting lower & lower Or does it try to save itself with a See-Saw type idle?

-the engine runs fine with no intervention when I do a cold start. It runs at 1,000 or just below 1,000 with consistency, and then, at normal operating temperature, it slows and stalls within 10 seconds of the first sign of RPM change.

Check EGR pipe between intake manifold and EGR valve. It usually has a heat insulating wrap around it so its hard to see. May have to remove the tube to be sure, 2 bolts /2 nuts.

- Yes, I removed the EGR pipe and checked for obstructions, wear, pin holes, damage. With the exception of the gasket (did not replace the gasket) there was no seemingly visible damage. I cleaned the pipe, however, it did not need cleaning.

Another vac leak source is a short rubber hose (with 90 degree bend) hidden behind the throttle body. connecting it to the intake manifold.

- yes, I know this hose, and I removed it and assessed it when I took the intake cover off. It was flexible, not rotted or torn or brittle. It fit properly and had no visible defect.

Check for proper grounding. Replace broken or missing ground straps. Engine block to frame, body to frame and chassis , etc. Can also check with a cheap Harbor Freight meter set to ohms.

- Okay, this one needs intervention. I read about grounding and have some grounding from the engine to the chassis. So, to have the engine properly grounded, please share with me where the grounds are supposed to be, and I will confirm that I have the proper grounding for proper engine functionality.

Note: I have checked the charging by testing voltage at the battery with the engine running using my volt meter. I get 13.3 to 13.8 volts fluctuating between those two points. The engine has never not started even though the car sits for long periods of time.

Note: I have sprayed carb cleaner on all of the vacuum connections and around the intake looking for a change in engine RPM to identify vacuum leaks. None to date.

Note: I have no oil leaks or water/fluid leaks. The engine heats up and does not smoke, either the engine itself or though the tail pipes.

Note: Each time that I start the engine, I have to turn the engine over several times to finally hear the fuel pump activate. For instance. First start (cold), I turn the ignition over for a few engine revolutions and release the key. No fuel pump engage. Second spin and release, no fuel pump, third, and sometimes a forth spin and no fuel pump. Finally I turn the ignition and release and hear the fuel pump activate. the very next time that the ignition turns the engine, the starts and keeps running until it gets to normal operating temperature when it eventually stalls. It will restart, but sounds and performs as though is is starving for gas or has an obstruction. At cold start, it runs for about 5 minutes with no problem.

Well, there you have it. Any ideas for a fix, please?
Patrick MAY 29, 02:10 AM

quote
Originally posted by altownsend:

Each time that I start the engine, I have to turn the engine over several times to finally hear the fuel pump activate. For instance. First start (cold), I turn the ignition over for a few engine revolutions and release the key. No fuel pump engage. Second spin and release, no fuel pump, third, and sometimes a forth spin and no fuel pump. Finally I turn the ignition and release and hear the fuel pump activate. the very next time that the ignition turns the engine, the starts and keeps running until it gets to normal operating temperature when it eventually stalls. It will restart, but sounds and performs as though is is starving for gas or has an obstruction. At cold start, it runs for about 5 minutes with no problem.



You have more than one problem.

The fuel pump should run for two seconds each time you turn the key to ON. Check the relay. You are presently relying on oil pressure to trigger the fuel pump. (It's a secondary fuel pump control.)

What is your fuel pressure, both while the engine is running, and after it's turned off?
altownsend MAY 29, 09:14 AM
Patrick,

Thanks for the question.

the fuel pump relay and the A/C relay were replaced. I replaced them before I replaced the IAC. And, Patrick, the starting process was the same before the relay was replaced. so, after a new relay was installed, the problem did not go away.

I do not remember the fuel pressure at the rail. I did, however, check it when the fuel pump pressurized the 'system', and while the engine was running. The reading was about the same. However, I will check it again and report the readings.
Patrick MAY 29, 04:04 PM

quote
Originally posted by altownsend:

the fuel pump relay and the A/C relay were replaced. I replaced them before I replaced the IAC. And, Patrick, the starting process was the same before the relay was replaced. so, after a new relay was installed, the problem did not go away.



Well, there's still something wrong. There are other people here who can describe the interplay in more precise detail... but when the ignition key is turned to ON, I believe the ECM energizes the fuel pump relay for two seconds. Your car isn't doing this, but the reason why you eventually get it to start is that once oil pressure is built up (from multiple engine cranks), it's the oil pressure sender which is energizing the fuel pump relay. However, I'm not sure if it's the same relay or not. I've never had these issues with any of my Fieros, so I don't know the finer details of the fuel pump electrical system.
altownsend MAY 29, 10:01 PM
[img]http://images.fieroforum.com/userimages/altownsend/Engine%20Runni ng%20Unplugged%20Throttle%20Position%20Sensor.jpg[/img]

Based on new information from this post, I ran three tests:

1) I screwed my fuel pressure gauge to the fuel rail fitting. I turned the engine over a few times and finally heard the fuel pump activate. I checked the fuel pressure gauge and there was no reading. The engine started and I looked at the pressure gauge and saw the gauge reading 45PSI. While the engine was running, the gauge went from 45PSI to 50PSI down to 40PSI at the higher RPM idle with the idle speed sensor unplugged.

2) I unplugged the idle speed sensor and the car ran for about 30 minutes at which time I turned it off. I re-attached the idle speed sensor, and the engine started buy stalled almost immediately. I unplugged the idle speed sensor, and the RPM stabilized and the engine kept running.

3) In the photo labeled "Filter of some sort', there is a filter that is attached to a hose that is connected to either the fuel rail or the intake. Can someone tell me what that filter is for (what it filters)?
Patrick MAY 29, 10:40 PM

quote
Originally posted by altownsend:

I screwed my fuel pressure gauge to the fuel rail fitting. I turned the engine over a few times and finally heard the fuel pump activate. I checked the fuel pressure gauge and there was no reading. The engine started and...



No fuel pressure and it started?


quote
Originally posted by altownsend:

...idle speed sensor



What exactly are you referring to? The idle control valve? The throttle position sensor?


quote
Originally posted by altownsend:

In the photo labeled "Filter of some sort'...



???



quote
Originally posted by Patrick:

What is your fuel pressure, both while the engine is running, and after it's turned off?
altownsend MAY 30, 12:59 AM
Patrick.



No fuel pressure and it started?
- yes, fuel pressure was 45PSI when I looked at it after the engine started. It could have built up as the engine was spinning.


...idle speed sensor
-see photo, throttle position sensor (the one sensor on the top)




What exactly are you referring to? The idle control valve? The throttle position sensor?
- throttle Position Sensor - when I unplug it, the engine runs for as long as I let it, at a higher RPM


In the photo labeled "Filter of some sort'...
- the silver filter. It does not filter liquid (gas). Is it an air filter? One end goes under and into the cabin, the other to the intake plenum


What is your fuel pressure, both while the engine is running, and after it's turned off?

-While running with the Throttle Position Sensor plugged in, 45PSI
-With the Throttle Position sensor unplugged, 40PSI
- it was at 50PSI at one point

With engine off, it stays at 45PSI, and then it gradually falls to under 30PSI over a period of time
Patrick MAY 30, 02:55 AM

quote
Originally posted by altownsend:

With engine off, it stays at 45PSI, and then it gradually falls to under 30PSI over a period of time



"Under 30PSI"? How far under?

"Period of time"? Are you talking two seconds, five minutes, one hour?

These questions are to help determine if you have fuel leaking from injectors, regulator etc.