Help diagnose fuel/alternator issue

hasonic

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Hello guys hope you're all doing well. I been doing some research in the forum and im kinda of narrowing it down to possible fuel pump issues but want to get second opinions before i start going crazy and rip everything apart.

I bought the car about 2 months ago. Car was running very well, good drive ability and solid power across the board. Long story short alternator took a massive dump on me.

Now, i replaced the alternator with a kenneth miley 3g/3.2 pulley and the big 3 wire of my own. When cold it holds 14.5/14.4 at the battery post and about 13.9 to 14.0 at the sct4. after it warms up it starts to drop the more things i turn on all the way down to low 12s and even dying on me.

Now i was checking my sct out and started noticing that my fuel pressure was mid teens and my fuel pump duty cycle was jumping from .20ish to .50 as my pump voltage would jump from 13.5 to 6 volts. So i did a log with the car completely cold assuring good alternator voltage and no accessories on. hoping some can point me out in the right direction.
 

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*Jay*

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Start looking over all of your battery, alternator and starter wiring both positive and negative. Also start inspecting everything that looks like a ground. Go as far up/down the wiring as you can, look for any hard kinks, bulges, damage, melting and random bits of tape. I had a total hackjob done on my wiring by the previous owner with what I am assuming was a big stereo or trunk battery install.

Screenshot_20200728-104354_Drive.jpg
 

hasonic

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Start looking over all of your battery, alternator and starter wiring both positive and negative. Also start inspecting everything that looks like a ground. Go as far up/down the wiring as you can, look for any hard kinks, bulges, damage, melting and random bits of tape. I had a total hackjob done on my wiring by the previous owner with what I am assuming was a big stereo or trunk battery install.

View attachment 1657784

Thanks for the heads up, I'll double check. I kinda went through it already and the wiring looks pretty much untouched.

I rechecked today and I discovered I have a vmp BAP. Im still getting that intermittent spike in fuel pump duty cycle and rail pressure. Even with the car cold and alternator charging 14 volts it's happening. Im leaning towards a pump going out but also wondering if the relays related to the fuel system fail normally on these cars. How about the bap, do the fail normally?

Can anyone else look at my log and give their 02?
 

*Jay*

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Get your charging system checked out at a parts store, not sure how much a fuel pump can affect charging but these cars are notorious for toasting alternators.
 

olympic

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Your FPDC and pump voltage are cycling wildly up and down at a fairly constant rate. Likely the BAP is failing or has bad wiring connections. Check its ground and the splice connections into the fuel pump harness. After that use a multimeter to check the voltage coming into and out of the BAP while the car is running.
 

MG0h3

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You need to use a voltmeter to check for voltage drop. Perfectly good appearing connections can be dropping a ton of voltage.


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GNBRETT

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Check the little plug that goes into the alternator sometimes the little clip breaks off and it will rattle out slightly and check ur alternator wire itself.

Ur fuel problems are voltage related which are charging system related.

Ur alternator may be failing as well. Ive killed two alternators before I went to a 240 amp.
 

hasonic

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Get your charging system checked out at a parts store, not sure how much a fuel pump can affect charging but these cars are notorious for toasting alternators.

Already replaced with new kenneth 3g/3.2 pulley setup. Same setup that I replaced. Took out old alternator and tested it out with my current battery and both passed. Charges when engine bay cold, but when it heats up it goes downhill.

Your FPDC and pump voltage are cycling wildly up and down at a fairly constant rate. Likely the BAP is failing or has bad wiring connections. Check its ground and the splice connections into the fuel pump harness. After that use a multimeter to check the voltage coming into and out of the BAP while the car is running.

Kinda did that but I will double check again cause I just randomly tested it. Is there a hyperlink to all our wiring so I can trace the fuel pump diagram from start to finish?

You need to use a voltmeter to check for voltage drop. Perfectly good appearing connections can be dropping a ton of voltage.


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Will be doing that

Check the little plug that goes into the alternator sometimes the little clip breaks off and it will rattle out slightly and check ur alternator wire itself.

Ur fuel problems are voltage related which are charging system related.

Ur alternator may be failing as well. Ive killed two alternators before I went to a 240 amp.

Most definitely are but I have a brand new 3g 200 amp upgrade from kenneth that many people here have had good results with. I been doing my test only when the car is cold and the alternator is charging 14v plus.
 

hasonic

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Do you have a battery light on after you start???

No at all, even when voltage drops into the 12s, i did the big 3 wire kit with 2 gauge. Do we have the wiring diagrams for the cobras here on the site or where can I find them?
 

01yellercobra

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Already replaced with new kenneth 3g/3.2 pulley setup. Same setup that I replaced. Took out old alternator and tested it out with my current battery and both passed. Charges when engine bay cold, but when it heats up it goes downhill.



Kinda did that but I will double check again cause I just randomly tested it. Is there a hyperlink to all our wiring so I can trace the fuel pump diagram from start to finish?



Will be doing that



Most definitely are but I have a brand new 3g 200 amp upgrade from kenneth that many people here have had good results with. I been doing my test only when the car is cold and the alternator is charging 14v plus.
Just because it's new doesn't mean it's good. Having the voltage drop as things heat up is a good sign it's the alternator. I've had the same issue in the past and it was the alternator.

Fix your voltage issues and I bet everything else will come in line.

I don't think the light will come in until voltage drops into the 11's. I remember when mine hit the 12vdc range I didn't see the light.
 

hasonic

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Just because it's new doesn't mean it's good. Having the voltage drop as things heat up is a good sign it's the alternator. I've had the same issue in the past and it was the alternator.

Fix your voltage issues and I bet everything else will come in line.

I don't think the light will come in until voltage drops into the 11's. I remember when mine hit the 12vdc range I didn't see the light.


I agree about the new alternator being bad, gonna get a replacement from kenneth but my data log shows that even at start up, when the engine bay is cool and the alternator is charging 14 volts the same symptom occurs. The voltage shown at the ecu stays in the 14 give or take .2 volts and the pump gets mid 13 volts and suddenly drops to 5 volts and shoots back up right away while the voltage at the battery is still in the 14 volt range.

Am i wrong to think maybe some relay along the fuel wiring harness might be going off, i heard theres like 2 or 3 relays related to the fuel system my car has already 73k miles.

Im trying to find that wiring diagram for the fuel system so I can start from the beginning and trace it all the way to the pumps.
 

MG0h3

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I would think a relay would just fail open, not give partial voltage.

Never know though.

Are you seeing the 5 volts at the pumps or feeding the FPDM?

If it’s at the pumps, I’d look at voltage feeding the FPDM while experiencing the 5 volts at the pumps.

The swinging back and forth suggests a control issue to me, something the FPDM could be doing.

On the other hand, I would not expect the circuitry itself between the fuse block junction and pumps to cause what you are describing.


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c6zhombre

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You have a lot of possibilities here for issues.....are the pumps themselves the original factory? If so, they're near 18 years old and it's not a matter of if but when they fail. Once you get the alternator issues ironed out one way or the other....you might want to invest in a full return fuel system with brand new pumps. You're asking a lot running an aftermarket blower, time to upgrade the feeding.
 

Albatross

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Is your BAP wired before or after the Fpdm? I know it can cause issues if wired after the Fpdm. Just an idea of something to check also.
 

hasonic

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Thanks for all the suggestions guys. so i traced the fuel pump wiring system from fuse on engine bay all the way down to connector on the tank right before the pumps. all the wiring had 13.5 +/- volts up to the BAP (BAP is pre FPDM) after the BAP the wiring was 18 volts up to the fuel pump connector.

What i did notice was that the voltage from the red and black wire that connects the pump to the FPDM was all over the place from 1 volt to 11 volts just swinging wildly. isn't this the ground wire for the pump?

I have no clue if these are original pumps but the car makes 599rwhp so not sure. And yes i am looking into a return system but not sure if to do so now or later.

while checking the fuel pump connector i saw one of the wires had a 5.2 volt reading so im guessing thats what you're talking about, correct?

I did notice the my iat sensor is not plugged into the intake, is that a common thing when modding, i have a jlt intake.

I also noticed the FPDM got hot enough to where you touch it for a few seconds you have to let go.

At this point i am really leaning towards the fuel pumps, unless the 02's are going bad but my short term fuel reading are both even on my sctx4. I dont think a fuel filter will cause such fluctuations

Any other suggestions before i drop the tank?
 
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03cobra#2

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I know you probably don't want to hear this but if you are going to drop the tank I would probably just do the return system. You get to the point with these vehicles (the age) that you may just want to go ahead and overhaul the fuel system. They make return systems that can use the existing fuel line and fuel rails to make the switch much easier....of course you will need a retune but you will be set. Make sure you get a new filler neck gasket and don't reuse the old one.
 

MG0h3

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Pin3 is pump ground.

Pin10 is pump positive.

I never had to deal with issues with mine so I’m not totally familiar with how far they modulate the voltage.

Those wild swings do seem a little erratic and I have seen people say extreme heat is a sign of failure.

If you ping MalcolmV8, he can probably the question I posed.

Black306 makes and sells modified FPDMs so he would be a good source of info as well.


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MG0h3

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Ok, I just read back through this whole thing.

I find it hard to believe we had a charging issue and fuel delivery issue develop simultaneously.

It sounds like you’re still seeing very low voltage and stalling? I guess we need to know if there is a fuel problem causing low rpm/low voltage and then stalling OR we have a voltage problem causing all of this.

If you’re holding correct idle rpm and your voltage is falling off, I’d address that and THEN move to the fuel issue if it still exists.


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