Firebird Nation banner
1 - 20 of 20 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
I apologize in advance if providing too much information, but hopefully someone can help me out.

1995 3.8l base model firebird...cold air intake tube from ebay, k&n air filter....this is where it all started...with cold air setup, car would idle like crap, i could disconnect mass air sensor and it would run good but get terrible gas milage...so i decided to put stock air box setup back on...did..car ran fine for a day...wake up next day..car wont crank...getting terrible clattering sound from fuel relay and pump wouldn't prime or anything...new relay and had same results...something was causing it to lose voltage from pcm....now the relay has 4 wires going to it...blk/wht-ground to chassis, pink-constant hot, grey-to fuel pump and drkgrn/white-signal wire from pcm...we probed all wires with key on engine off(obvious since car wont start) and all seemed to be fine but...the pcm signal wire(drkgrn/wht) was getting 2 different readings....when probed to negative battery terminal, we were getting 10.xxVolts which i believe it should be a full 12v...so for shits and giggles we probed to the positive bat terminal from the same pcm signal wire(drkgrn/wht)...its getting 2.xxVolts....now im not the smartest man in the world, but i pretty sure we shouldnt get 2 different currents over the same wire from the pcm and also i know without the car running, i should only get signal from the pcm signal wire(drkgrn/wht) for 2 seconds to prime fuel pump then should be nothing....thats not the case...it gets current all the time just not when key is all the way off....so we think okay, there must be some sort of short or grounding issue somewhere...so while investigating, we found the wiring harness that runs behind the crank pulley under waterpump had all be exposed and covered in years of oil and dirt..we clean it up cover all wires continue checking for cuts, corrosion and everything...nothing....everything "seems" to be good...but car will not start...i can turn the fuel pump on by connecting 12v to the prime wire under hood but even with that it will not start...car will try to crank but with no result...fuel line has pressure..fuel pump is less than a year old..so now im not sure what exactly im asking but I need help...im completely lost..could i have really messed something up putting stock air box back in? like really? i checked all wires by the relay box and ones that run under the air box, all seems to be fine....now i did at one point figure out that if i unplugged the air temp sensor while the relay was rapidly clicking it would stop..then plug it back in and it would start again...but it only did it those 2 times..after that it had no effect to anything...is my pcm shot? or is there a possiblility that a wire some where is exposed or corroded that is making the pcm send positive and negative signals down the same wire(drkgrn/wht) or is that how it is supposed to be? HELP
 

·
Administrator
1994 Firebird Formula 381ci LT1 / TH400+GV O/D
Joined
·
14,425 Posts
Have you actually measured the fuel system pressure? Is the SES light on? Have you scanned it for codes?
 

·
Ramblin' Wreck
Joined
·
5,083 Posts
but...the pcm signal wire(drkgrn/wht) was getting 2 different readings....when probed to negative battery terminal, we were getting 10.xxVolts which i believe it should be a full 12v...so we probed to the positive bat terminal from the same pcm signal wire(drkgrn/wht)...its getting 2.xxVolts....now im not the smartest man in the world, but i pretty sure we shouldnt get 2 different currents over the same wire from the pcm ...

or is there a possiblility that a wire some where is exposed or corroded that is making the pcm send positive and negative signals down the same wire(drkgrn/wht) or is that how it is supposed to be? HELP
You thinking is messed up there. Current and voltage are not the same. Don't confuse them. Current (amperes) is the flow rate through a wire. Voltage (volts) is the potential between two places. When you measured the first time referenced to ground and got 10.xx volts, then measured the same wire referenced to battery positive and got -2.xx volts, that was perfectly normal. The difference between the two numbers will be the battery/alternator voltage 10-(-2)volts=10+2=12volts. To minimize confusion, always measure referenced to ground. Current can only be measured in a wire by cutting or separating it somehow and inserting the meter between the two pieces. Rarely do we have to measure current unless we are checking for alternator charge rate or tracking down a short.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #4 ·
no have not measured fuel pressure...fuel pump is not even kicking on....when i use the 12v prime under hood it turns on but wont start...no throwing any codes and no lights on that shouldnt be...no ses no security or any of that jazz
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #5 ·
You thinking is messed up there. Current and voltage are not the same. Don't confuse them. Current (amperes) is the flow rate through a wire. Voltage (volts) is the potential between two places. When you measured the first time referenced to ground and got 10.xx volts, then measured the same wire referenced to battery positive and got -2.xx volts, that was perfectly normal. The difference between the two numbers will be the battery/alternator voltage 10-(-2)volts=10+2=12volts. To minimize confusion, always measure referenced to ground. Current can only be measured in a wire by cutting or separating it somehow and inserting the meter between the two pieces. Rarely do we have to measure current unless we are checking for alternator charge rate or tracking down a short.
ok cool so then my pcm wire in theory should be able to get the full 12v from battery then..do i need to measure the current from the relay back to pcm? i have exposed spots on both wires ive made for testing if needed?

in my relay the pcm lead(drkgrn/wht) and the ground(blk/wht) should charge the magnet inside the relay and allow current to flow from pink wire to gray wire..so either the pcm lead wire not getting power from pcm when its supposed to or the ground is bad(but had spliced a diferent ground for that wire during some earlier testing back to original wiring now)
 

·
Administrator
Joined
·
2,476 Posts
Sounds like you need to download the Factory Service Manual and follow the appropriate diagnostic flow-charts. Those flow-charts will detail everything you need to do, what to look for, what to measure, where to measure, what values to expect, what to do if they are out of spec, etc. If you can pull a trouble code, it gets even easier.

...not every condition / code will illuminate the SES light. Scan anyway. While on SES, does it light up with first key-on and go out after a couple seconds? Every time I hear "No SES" I think: Maybe it's burned out. ;)

PCM hardly never goes bad. This is more likely something you have caused (started w/cold-air, got better when OEM airbox reinstalled) or more likely exasperated with the cold air install. Check every wire in and around the area the cold air kit / factory airbox location. You may have something randomly shorting/grounding. You may have pulled a connector or damaged one or a wire or pinched something somewhere without realizing it.

Do other things break when something else is repaired/replaced? Sure. Happens all the time. Usually related though. Can a fuel pump or something else break with the cold-air install? Sure. Related? Not likely. Scanners are our friends.

Most likely this is something simple and stupid that is 100% related to your "modification". Get out there and go over every millimeter in the engine compartment that you were working around. You could have set something on the motor, picked it up, and snagged something without realizing it. FSM will see you through this. It is an *amazing* resource.

Good luck.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #7 ·
Sounds like you need to download the Factory Service Manual and follow the appropriate diagnostic flow-charts. Those flow-charts will detail everything you need to do, what to look for, what to measure, where to measure, what values to expect, what to do if they are out of spec, etc. If you can pull a trouble code, it gets even easier.

...not every condition / code will illuminate the SES light. Scan anyway. While on SES, does it light up with first key-on and go out after a couple seconds? Every time I hear "No SES" I think: Maybe it's burned out. ;)

PCM hardly never goes bad. This is more likely something you have caused (started w/cold-air, got better when OEM airbox reinstalled) or more likely exasperated with the cold air install. Check every wire in and around the area the cold air kit / factory airbox location. You may have something randomly shorting/grounding. You may have pulled a connector or damaged one or a wire or pinched something somewhere without realizing it.

Do other things break when something else is repaired/replaced? Sure. Happens all the time. Usually related though. Can a fuel pump or something else break with the cold-air install? Sure. Related? Not likely. Scanners are our friends.

Most likely this is something simple and stupid that is 100% related to your "modification". Get out there and go over every millimeter in the engine compartment that you were working around. You could have set something on the motor, picked it up, and snagged something without realizing it. FSM will see you through this. It is an *amazing* resource.

Good luck.
Thanks for you reply! I check for codes every time I try to start it and before i give up...i used to throw a code for the coolant temp sensor but found it was exposed near the connector and repaired..now nothing..no codes...As for the hunt for what I did..yep..that pretty much what I am doing..I have been at it for 4 days now trying to figure out what I did...im pretty sure its something I did..as it always goes with my car...just trying to narrow down the hunt lol...i drained my battery earlier trying different things to get it to start..gonna take to the zone tomorrow and have it charged and back at it tomorrow....ill update with any findings...i appreciate everyones help and input please if you have an idea or something you think may help let me know....where would i find the factory service manual?
 

·
Administrator
Joined
·
2,476 Posts

·
Administrator
1994 Firebird Formula 381ci LT1 / TH400+GV O/D
Joined
·
14,425 Posts
Let's try and organize this a bit better - can be hard to follow one giant paragraph:

What is the problem:

- with cold air setup, car would idle like crap,

- i could disconnect mass air sensor and it would run good but get terrible gas mileage...

- put stock air box setup back on...did..car ran fine for a day

- wake up next day..car wont crank.

- getting terrible clattering sound from fuel relay and pump wouldn't prime or anything.

Let's be clear on what happens when you turn the key to start (Correct if I'm wrong):

-starter engages

-??engine cranks, but will not start?? (not everyone uses the word "crank" the same way")

-??Does it make a sound like a plug is occasionally firing, and engine is popping, backfiring??

To start, the engine needs fuel, spark and compression.

-What is the fuel pressure? You indicate when you supply 12V to the fuel prime connector, the pump runs. Check the pressure at that point. It is more likely you have disturbed or damaged a wire near the front of the engine. And clearly if the pump does not prime when you turn the key to the "run" position, power is not getting there. That is the most disturbing part. Gary did note that your electrical analysis had errors, so I would recheck to insure that the load side of the relay (orange wire, terminal 87) is receiving 12V power, and the relay is passing the 12V through to the pump. so hook your volt meter up to the gray wire at terminal 30 on the relay, and a good chassis ground.

- Is the fuel pump relay still chattering

- have you checked the fuse for the fuel pump? Looking at the 96 manual (95 manual does not have the 3.8L engine, may have been issued as a supplement, because the 3.8L engine did not appear until late in the model year) it is fuse 3 (PCM BAT) in the instrument panel box.

-Have you checked for spark at several of the plugs?

Let's assume nothing you did affected the compression.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #10 ·
Let's try and organize this a bit better - can be hard to follow one giant paragraph:

What is the problem:

- with cold air setup, car would idle like crap,

- i could disconnect mass air sensor and it would run good but get terrible gas mileage...

- put stock air box setup back on...did..car ran fine for a day

- wake up next day..car wont crank.

- getting terrible clattering sound from fuel relay and pump wouldn't prime or anything.

Let's be clear on what happens when you turn the key to start (Correct if I'm wrong):

-starter engages

-??engine cranks, but will not start?? (not everyone uses the word "crank" the same way")

-??Does it make a sound like a plug is occasionally firing, and engine is popping, backfiring??

To start, the engine needs fuel, spark and compression.

-What is the fuel pressure? You indicate when you supply 12V to the fuel prime connector, the pump runs. Check the pressure at that point. It is more likely you have disturbed or damaged a wire near the front of the engine. And clearly if the pump does not prime when you turn the key to the "run" position, power is not getting there. That is the most disturbing part. Gary did note that your electrical analysis had errors, so I would recheck to insure that the load side of the relay (orange wire, terminal 87) is receiving 12V power, and the relay is passing the 12V through to the pump. so hook your volt meter up to the gray wire at terminal 30 on the relay, and a good chassis ground.

- Is the fuel pump relay still chattering

- have you checked the fuse for the fuel pump? Looking at the 96 manual (95 manual does not have the 3.8L engine, may have been issued as a supplement, because the 3.8L engine did not appear until late in the model year) it is fuse 3 (PCM BAT) in the instrument panel box.

-Have you checked for spark at several of the plugs?

Let's assume nothing you did affected the compression.
- car will crank as in starter engages and motor turns but never fires up...no pops or anything

-checked every fuse in car multiple times all are good

-car is '95 bird with original 3.8l engine in it im assuming mine was towards the end of the 95's production life(sure not important but either way lol)

-relay is no longer clattering or anything...i have taken off the casing to see what exactly the relay is doing..now its not clicking over like it should dunno why because i hadn't done anything from when it was clattering to now(other than testing and checking wires)

-i can force the relay to click over if i apply a 12v+ led to the post where green wire should go but even with that car never starts

-not sure if because batt was running low or not but last night while trying to crank was getting a weird thumping sound every 2-3 seconds

-i dont have a gauge for anything to test fuel pressure but if i clear fuel lines, then prime pump, then release pressure from the valve on fuel rail gas shoots out like a fountain(so hopefully its good...pump is less than a year old with lifetime warranty may just exchange it to cover that basis?)

-i have not check the spark plugs yet because pump is not turning on by its self i have to use the prime line or jump the relay to get it to work

-terminal 87 for me is pink not orange have tested getting 12v as well as gray wire getting 12v
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #11 ·
one thing i fell i need to mention that i forgot

a few years ago fans stopped working so i wired them to a toggle switch under my dashboard....dunno if that makes any difference...havent had any problems out of them or my car since then
 

·
Administrator
1994 Firebird Formula 381ci LT1 / TH400+GV O/D
Joined
·
14,425 Posts
-terminal 87 for me is pink not orange have tested getting 12v as well as gray wire getting 12v
When do you have 12V on the gray wire? Should only have it 1) if you apply 12V to the signal side of the relay; 2) 12V applied to the prime connector; or 3) the PCM applies 12V to the signal side of the relay. If you have 12V at the gray wire, and the PCM is applying 12V to the signal side of the relay, the pump should be running.

I found the supplement to the 95 factory manual for the 3.8L V6. Clears up the issue with wire colors:

.
 

Attachments

·
Registered
Joined
·
14 Posts
Discussion Starter · #13 ·
***UPDATE***

The Bird is finally back up and running. After many many many hours of testing and frustration.

* I pulled entire pcm wiring harness and exposed all wires.

*Crankshaft position sensor - all wires were exposed and shorted together.

*Not sure what connector but goes in the tail end of tranny on the side - both wires were exposed and shorted together.

*was having no luck even after fixing those issues

*hooked it all back up to just see what it would do and tada nothing

*put obdII scanner on it to check for codes - gave a read error(first time ever)

*after researching I decided to check wires for the obdII plug

*My dumb self forgot to turn key off or disconnect battery first but the fuel relay started clicking as i messed with wires up under dash

* pinpointed the wiring causing the relay to click off and on...it is the black wire that leads into the relay...apparently the wire must be broken where it goes into the connector because if i bend it in half, works like a charm. I did at one point bypass the connector and wired up my own connector using single pigtail connectors but it never did anything. I really think that the crankshaft sensor, tranny things and the negative wire on relay were all causing the problem. My car also used to have a weird stutter during warm up and it has seem to have gone away. After much work, frustration and determination, I finally got my baby running strong. I haven't replaced the relay harness yet..making trip to junkyard tomorrow =)

Thank you FBN for all your help. Everyone here was extremely helpful and really if it wasn't for y'all, I would have prolly took her to the junk yard. Thanks Everyone!
 

·
Administrator
Joined
·
2,476 Posts
Glad you got it sorted.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #15 ·
Update....so the bird still not fixed...I've been through entire pcm harness and everything looks okay

When fuel pump relay is clattering...the obd2 will give a no read error on the scanner..car will start but the fp relay clatters every few seconds and car stutters and revs up...ill see if I can get a video up soon of it...I'm beginning to think my pcm may be causing my issues...local junkyard sells used for $30 so I think I'm going to try that. ..any ideas or input wpuld greatly help
Also my cruise control stopped working about a year or so ago...not sure if related or how it could be but just trying to provide any info that may help
 

·
Administrator
1994 Firebird Formula 381ci LT1 / TH400+GV O/D
Joined
·
14,425 Posts
What does this mean:

When fuel pump relay is clattering...the obd2 will give a no read error on the scanner..
Do you mean there is no code set for the fuel pump? If so, there is no code for a faulty fuel pump, or for loss of fuel pressure.

Or, do you mean the communication with the ALDL link is lost?

The connector on the tailshaft of the trans is most likely the vehicle speed sensor (VSS). You indicate you lost the cruise control a year ago? Did you also lose the speedo, or experience intermittent failure of the speedo? There is a code for the VSS. Did it ever show on your scanner? I don't see any of this causing the fuel pump relay to chatter.

You reference the black wire on the fuel pump relay. Do you mean the black wire with the white stripe? What did you do to fix that wire's intermittent loss of ground?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #17 ·
I did not lose spedo..still works...I cannot communicate with obd2 at all...just says communication error...when fuel pump relay is not clicking I can read codes on obd2 but just tells me no codes to display

The black/white wire to fp relay had a bad connection within the harness..it was frayed and barely attached...I pulled that pin out..recrimped the wire in the pin and put it back in harness

Sent from my SCH-S968C using Tapatalk
 

·
Administrator
1994 Firebird Formula 381ci LT1 / TH400+GV O/D
Joined
·
14,425 Posts
I think you may still have a problem with the black/white ground wire, or a connector in the dash that it passes through.. That wire is identified as circuit "451" in the fuel pump wiring diagram above.

On the ALDL connector diagram in the 1995 3.8L factory manual supplement, there is a black/white ground wire that is also identified as circuit "451". It connects to pin 5 in the ALDL connectors. That circuit is also the source of multiple PCM grounds. Circuit 451 grounds at the right front of the engine block.

The black/white ground wire goes through instrument panel connector #3, pin B, before it goes to the ALDL connector and the other things that it grounds. This connector could be the problem.

Did you actually find a broken wire when you repinned the connector for the fuel pump relay?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #19 ·
New pcm....no more issues...confirmed....pcm off a 97 camaro....just popped it in and my bird ain't never run this good...I think the electrical shorts fried the pcm

Sent from my SCH-S968C using Tapatalk
 

·
Administrator
Joined
·
3,302 Posts
Have you checked the pink wire that powers relay points. It runs to fuse 5 of ip fuse box.

If the pink wire intermittently losing power then getting power back while pcm is commanding fuel pump on, then points would open & close rapidly. Thus the clicking noise.

Same is true if dark green/ white wire from pcm to relay coil is intermittently losing power. This power energizes relay coil causing magnetic field that closes relay points. Same as above, if power is lost to relay coil intermittently and then re established, points would open and close rapidly.
 
1 - 20 of 20 Posts
Top