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Discussion Starter · #1 ·
I have a 88 bird with 305 tbi I want to do a rebuild with new gaskets and replace the fuel pressure regulator spring along with new fuel injectors. I have been have issue with the idle and I just want to try fix that at the same time. What is a good rebuild kit and how do know if I can use a higher psi fuel pressure regulator spring.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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What is the specific issue with the idle - rough, incorrect idle speed, stalling???

With regard to the fuel pressure regulator, have you checked the fuel pressure? What makes you feel it needs to be replaced? What benefit do you feel there would be in a higher psi spring?
 

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GM fuel injection strategy for fueling, at least doing the time your car was built, was based on having as consistent a fuel pressure as possible. And fuel pressure at the correct psi reading.

Raising or lowering the fuel pressure will alter the amount of fuel being sprayed during injector on time. However the computer that is expecting the proper pressure will get data from sensors saying fuel mixture is not correct. Computer will add or subtract fuel, but will never get the correct mixture because fuel pressure is not correct.
 

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Ok thanks I need to know if tis the sock 12psi I have th LO3 305v8. Yes it will stall out after the car is up to temp I found the idle screw that helps a lot but the idle goes up and down from like 600 rpms to 300 when stopped. Also would low compression in one of the cylinders make that happen ? One is a bit low it was at about 96 psi dry tested but the others tested fine. I still want to replace the gaskets and put new injectors anyway.
 

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Have you put your car on an obd 1 scanner that does real time sensor data? That way you can see if any of the sensors and actuators are not working correctly.

I'd pay close attention to the iac counts. (idle air control) If iac is not working correctly, idle can be all over the place. Also engine can stall when you let off the gas.

Vacuum leaks will also mess with the air/fuel mixture. This causes erratic running.
 

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Discussion Starter · #6 ·
right I might have a friend that has one but the snap ons are about 150 on ebay so ill wait till next year but ill check the voltages also not sure what else it can be but any other ideas are welcome just very annoying issue.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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What psi did you get on the 7 cylinders you feel were "fine" on the compression test?
 

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Discussion Starter · #8 ·
all of the 7 cylinders have over 120 psi of compression the service manual said that anything above 100 psi was fine.

Also I did buy a mt2500 for 180 it seemed like a good deal most of them sell for over 200 easy so ill use that and check to see what the iacs are.
 

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Hopefully you bought one that includes the power hook up cables and 12 pin obd 1 GM connector. If not, these are available separately on ebay and other sites.
 

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Discussion Starter · #10 ·
I have the code scanner and it shows erg malfunction and tps sensor voltage issue so should I post the real time data?
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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all of the 7 cylinders have over 120 psi of compression the service manual said that anything above 100 psi was fine.
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When you do a compression test, you are looking for significant differences from cylinder to cylinder. The fact that you have one cylinder that is 20-25% lower than the other 7 cylinders is pointing to a possible problem with that cylinder. You need to look into it further.
 

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Unfortunately, unless you can post an entire data log that can be viewed in real time, it will be difficult to make any suggestions. Unless you have data for a or some sensors that's way out of the norm.

And keep in mind that incorrect data from a sensor can be caused by wiring, connectors, grounds, power supplies, etc.

Did you use the MT2500 to test your actuators while you were using it?
 

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Discussion Starter · #13 ·
I can take screen shots I don't have a data cable or printer for it. What is the actuators test ?

I have to wait till the snow melts some so I can run it, but I have the user manual for the scanner and the guide for troubleshooting.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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There are codes for TPS voltage low and high. Which did you get? What is the TPS voltage at idle? Key on/engine off rotate the throttle to wide open. What is the voltage? Does the scanner show IAC counts? What are they at idle? Is the reading steady or is it moving up and down?

Hard to tell if the EGR code is for EGR flow or for the electrical circuit for the EGR solenoid. Check the harness connector at the EGR valve. Key on should have 12V on the pink/black wire. Harness off the solenoid, measure the resistance of the solenoid and report back. This problem is not likely to be causing the idle issues, unless the solenoid is stuck open. At idle there should be no vacuum on the EGR side of the solenoid. A stuck open EGR gave will cause rough idle or stalling. It would also cause an EGR fault if the code is based on detecting EGR flow.

Try posting a screen shot at idle.... better than nothing at all.
 

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If actuator test is available for your year, make, model, engine, it will come up in the list of functions of scanner.
 

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Discussion Starter · #16 ·
Ok Thanks I will try that. Also what would cause my valves to be white like this? I checked each on the driver side of the block and they all were the same color.
 

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Discussion Starter · #17 ·
I got some pics with the data so i did replace a relay but i don't think it was the fuel one. also i found this in the book so looks like its not getting 12 volts i have not checked it .

Circuit Description:

When the ignition switch is turned "ON", the electronic control module (ECM) will activate the fuel pump

relay and run the in-tank fuel pump. The fuel pump will operate as long as the engine is cranking or running,

and the ECM is receiving ignition reference pulses.

If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after key "ON".

Should the fuel pump relay, or the 12 volt relay drive from the ECM fail, the fuel pump will be run through

an oil pressure switch back-up circuit.

Code 54 will set if the ECM does not see the 12 volts signal at terminal "B2" during the 2 seconds that the

ECM is energizing the fuel pump relay.
 

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Not easy to get much out of those. Can't see 1/2 the screen clearly. It appears to show the closed TPS at 0.62 volts. And it indicates that is within the acceptable range of 0.45 volts to 1.25 volts. That would not set a low TPS code. Hence the code for TPS low must be stored from a past event, and is probably intermittent. Clear the codes and see if it comes back.

Were you holding the pedal on the floor where TPS is 4.34 volts. I would expect it to be higher. Any chance your floor mat is under the pedal?

Best way to test the TPS is to use a volt meter at the sensor, reading between the signal wire and the black ground wire. Starting with the throttle closed, s-l-o-w-l-y rotate the throttle to fully open. Watch the voltage carefully for sudden dropouts (brief very low reading) and spikes (brief very high reading). Do it again while moving the harness connector. Loose pins can cause intermittent problems.

You idle air counts appear to be 17. Was the idle stable? If not, if RPM dropped, did IAC counts increase? I don't think I saw an RPM reading. Not a very useful way to read the data.

You are looking at the fuel pump (relay) and DTC 54? What problem is that for? I don't see that mentioned in the above posts. What's that all about?

Did you read my comments about the results of you compression test? Did you think about that as a possible problem?
 

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Discussion Starter · #19 ·
Yes I did have the pedal half way down to read at 4.34. also when the scanner was in the diagnostic mode it made the idle very stable and it did not go up and down. Also the code 54 I just had seen it there no sure about it also I don't know how to clear the codes. The compression test for cylinder number 3 was about 95 so would that offset the idle also ? I need to check the timing to but this idle issue has been going on for about 2 years now. I did adjust the idle screw and took off the foil cap because I was annoyed ever time when it would stall when you are stopped and the idle issue is when the car is up to temp not when cold. What data do you need from the scanner like tell me what ones you need to help more. thanks
 

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Discussion Starter · #20 ·
Also I tested the EGR solenoid and it had no voltage with the car running and with just the key on. One other thing is that every time I use the scanner and power it from the cigarette lighter outlet it blew out the 20amp fuse for the inside lights. At first I swapped the 12pin gm1 adapter and switched it out with one other I had and that didn't work. Then I use a different seral cable also so it seemed like there was a short in the cigarette lighter power cable. So I found that very odd and just used the power cable that you put on the car battery.
 
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