96 cobra breaks up under WOT

[Pedrothecobra]

Yea I made some jumpers at work today to fire it when I get home later. I ordered one just incase. I ohmed out the resistor and I’m only getting .4ohms not sure what I should be getting.

 

[Monday]

Have you looked at the capacitors in the computer? Two of them. I replaced mine when I did my intakes and never looked back.

You can get them off eBay

 

[Pedrothecobra]

So I tested the relay last night. It’s a normally closed, so no power and I have .2ohms across the wires. When I power it I have .900 mega ohms. Not sure what I should actually be getting if that’s supposed to be full open. I do have a new relay on its way

 

[Pedrothecobra]

The E

Have you looked at the capacitors in the computer? Two of them. I replaced mine when I did my intakes and never looked back.

You can get them off eBay

ECU is new

 

[ttocs]

there are normally 5 pins on the relay. pins 85/86 go to the coil and when energized make it click. The other three pins go to the switch contacts and two of them are common when it is not energized(pins 87a and 30) and two are common when they are energized(87 and 30). If your measuring the resistance on 87, 87a and 30 pins there should be next to no resistance on them when they are common.

 

[Pedrothecobra]

Yea I have no resistance when the relay is at rest and I should be reading open when the relay changes state which I’m not so I’m thinking it’s hanging up

 

[ttocs]

ok well to be sure we are not confusing our terms, no resistance = an open circuit. Its the same as if you were to hold the two ends of the meter with out touching anything, its open and will read infinite resistance.

But now again I am not sure what pins your reading.

 

[Pedrothecobra]

no resistance to me is .1ohm, usually what you get when you hold your meter leads together. OL would be an open circuit or if your leads were not touching anything, everything else in between is resistance lol.

 

[Pedrothecobra]

ok so UPDATE: im pretty sure this Schematic is wrong, the fuel pump relay is showing normally open. the relay in the car is a normally closed. that aside i took a voltage reading at the coil wires across the relay connector(pin 86/85) last night and i have 12V which is supposedly normal below 3200rpms. my issue is the voltage never goes away which should close the relay and allow full voltage back to the pump (cutting the resistor out of the circuit) while in the higher RPM range. so we pulled the relay and jumped the pins to send full voltage (pins 30/87a at relay connector) back to the pump, i only got 12.5V at the pump and im still dropping pressure when i lay into it. psi goes up to about 50 and drops to about 20 when im at WOT. took some resistance readings of the wires, starting at the CCRM and working my way back to the pump, wires all tested good. the interesting thing i found was i have a slight short to ground at pin 30 on the relay connector coming out of my PCM and by slight i mean 6.9kohms. i was curious because even with the relay out of the equation im only getting 12.5v at the pump when my body voltage is 14v. now ive shaken down and inspected most of the body harness involved with this circuit im not getting any change in resistance to ground while doing it. if i unplug the PCM it goes open which tells me this circuit is pulling a ground through it. (i have inspected all my grounds/connections and they all seem to be in good order. that being said if we circle back to the coil side voltage not dropping out at higher rpms.......looking at the drawing i assumed the signal to drop the coil voltage and close the relay came from the PCM. (wht/rd) but i see there is a red wire that comes from the CCRM that also supplies one side of the coil. now this schematic is decent but i cant determine who sends the output to remove voltage and close my relay bypassing the resistor. ( i want to get the circuit operating correctly before i start pulling apart harnesses) anyone have any deeper knowledge of this circuit? TIA...... hopefully this post makes sense to who ever is reading it lol

 

[ttocs]

if you jumped the relay then that is not the problem and it sounds as though you have the same problem with or with out it in place now?

How old is the pump and the hose attached to it inside the tank? I have to wonder if when the pump gets the higher voltage if it isn't creating enough pressure that it finds a leak either in the hose or the connection to it and its blowing out the extra pressure but back into the tank.

 

[Pedrothecobra]

correct. im never seeing full body voltage at the pump. pump was supposedly replaced at a shop about a month ago, i dont suspect it wasnt replaced but you never know... im still not sure where the signal comes from to remove voltage from the coil to close the relay and allow the circuit to bypas the resistor. im leaning towards the CCRM since the PCM is new


i do see the CCRM supplies one side of the injectors, im wondering if my issue is the injectors are staying wide open instead of pulsing causing the pump to not be able to keep up? and thats why im seeing the drop. car pulls hard during the drop while im easing into the throttle, its when i lay into it hard approaching WOT is when i see the drop, if that makes sense

 

[Adultingsucks]

Pedro's helper here. From what Pedro is saying, everything seems accurate. We confirmed that the leakage to ground on the LTGRN/Yel line at the fuel pump harness connector only appears when the PCM is connected, and all other circuits/connectors are isolated. I tend to believe that this small leak is a path to ground via PCM circuitry. What is unknown is the driving force behind the FPR relay coil. The relay is energized from startup (normal) opening the circuit path from the CCRM to pins 30 & 87a then ultimately to the pump. From what I've read, at >3250rpm, the PCM should cut the driving signal to the FPR, de-energizing that relay, and closing the circuit path from CCRM full body voltage to the pump. The FPR and Resistor are wired in parallel so as to create a low output/high output scenario from the pump. Looking at the CCRM I/O, I'm inclined to ask if the Tach signal into the PCM, or maybe it was the CCRM, is the driving force for the change. This tach signal is shown on page 1 of 2 from the book we are working through. If the tach signal isn't being processed correctly, or the CCRM is failing, I'm curious if this is what is keeping the FPR latched up.

I also agree with ttocs that having installed the jumper across FPR 30 & 87a, to supply full voltage to the pump, and not seeing that much of a difference, would point me in the direction of a fuel delivery issue. So in my mind, we have two issues on the table.

 

[Pedrothecobra]

Pedro's helper here. From what Pedro is saying, everything seems accurate. We confirmed that the leakage to ground on the LTGRN/Yel line at the fuel pump harness connector only appears when the PCM is connected, and all other circuits/connectors are isolated. I tend to believe that this small leak is a path to ground via PCM circuitry. What is unknown is the driving force behind the FPR relay coil. The relay is energized from startup (normal) opening the circuit path from the CCRM to pins 30 & 87a then ultimately to the pump. From what I've read, at >3250rpm, the PCM should cut the driving signal to the FPR, de-energizing that relay, and closing the circuit path from CCRM full body voltage to the pump. The FPR and Resistor are wired in parallel so as to create a low output/high output scenario from the pump. Looking at the CCRM I/O, I'm inclined to ask if the Tach signal into the PCM, or maybe it was the CCRM, is the driving force for the change. This tach signal is shown on page 1 of 2 from the book we are working through. If the tach signal isn't being processed correctly, or the CCRM is failing, I'm curious if this is what is keeping the FPR latched up.

I also agree with ttocs that having installed the jumper across FPR 30 & 87a, to supply full voltage to the pump, and not seeing that much of a difference, would point me in the direction of a fuel delivery issue. So in my mind, we have two issues on the table.

 

[Adultingsucks]

After looking at the photo of page 1 of 2, it seems that what I referred to on my earlier post about the tach may not jive. Looking at it, I would say now that is the output to the tach from the PCM. I think taking a look at the intake air temperature sensor or IAT sensor is necessary, and hasn't been done yet.

 

[ttocs]

it could also be as simple as a bad ground at the fuel pump. When you test for voltage there are you grounding the meter to the body or are you testing both wires going to it?

 

[Pedrothecobra]

it could also be as simple as a bad ground at the fuel pump. When you test for voltage there are you grounding the meter to the body or are you testing both wires going to it?

im testing it at the body. i have the ground wire from the cig lighter oicked up and a line ran back to the fuel pump. i may throw the meter on the fuel pump line and do a voltage drop test to see if im losing voltage from a possible bad connection. at this point i cant rule anything out

 

[Pedrothecobra]

After looking at the photo of page 1 of 2, it seems that what I referred to on my earlier post about the tach may not jive. Looking at it, I would say now that is the output to the tach from the PCM. I think taking a look at the intake air temperature sensor or IAT sensor is necessary, and hasn't been done yet.

im pretty sure i looked at that originally when i was doing data logs, we can look i have all of them saved

 

[Adultingsucks]

There are write-up on how to test the IAT I've seen online also.

 

[Pedrothecobra]

come on over

 

[ttocs]

check the voltage using both the power wires and see if its any different