I just got a new 7, its a 89 gtu turboII conversion. Its street ported, 3mm seals, race pinned, 850cc secondaries, cosmo fuel pump, apexi safc, full racingbeat exhaust etc, its very fast, my question is, sometimes around 4-5,500 rpm, it starts spitting and sputtering like its starving for fuel, i live in MO and the guy i bought it from lives in FL, when i got the car back to MO he mention that the fuel pump may be miswired (somehow?) he said that the pump may not be gettin the full 12 volts it needs to pop the secondaries off, i was wondering it there is something else that would cause that sputterin annoying s@#t i was thinking the fuel pressure regulator...the afc isnt tuned yet, ive only had the car around a week, im just trying to get the minor bugs worked out before i get into heavy tuning...sometimes it sputters, sometimes it boost just fine to 16 psi...im not sure what the problem is...any help would be greatly appreciated thanks brad

 

If it runs good for a while, then starts sputtering, etc...,check the inlet filter on the fuel pump first, that one just got me too....

 

just wondering wayne how would one go about cleaning that filter?

 

fuel filter? just replace it. you can't really clean them -- they work under the same basic principle as an oil filter.

one time use only.

 

do they sell them at autozone or someplace like that? and we arent talking about the fuel filter that is in the engine ba. we are talking about the one in the fuel tank that is connected to the fuel pump.

 

well, when i had 850's in my secondaries, it sputtered like crazy at about 6k in first and sputtered 500rpm lower in second, another 500rpm lower in third and so on. i was running mad rich tho and was flooding the motor out. with the mods you've listed, i feel you are having the same problem as me. injectors are just too large until you tune it out with the AFC or get smaller sec.

 

oh, the tank filter can be cleaned, but with injectors that big, fstrnyou is right. you gotta tune those suckers down some.

 

If you suspect the Fuel Pump Is leaning out on you, than tee a 0-6psi guage on the feedline. Tape the guage on to the windshield. At 2nd and 3rd gear - awhile at WOT, see If your fuel pressure (whatever It was at Idle) does not go below 5psi. On streetported Engines, the pressure drop should not go below 30% from the Idle pressure. This, according to Racing Beat.

 

where can i attach a multi meter to my fuel pump to see what kind of voltage it is getting?

 

i guess you could tap into the plug in the left rear corner. i don't see how that would hurt anything, have a friend ride along to read out the voltage while you drive.

 

the left rear corner of the car?? i mean i know where the fuel pump is but im not sure exactly where you are talking about. if you could clear it up that would be great

 

Follow the fuel pump harness to its connector. It's under the rug on the back of the left rear strut tower. The large Blue wire on the chassis harness is the power wire.

You should read about 9volts at idle and when not under boost. Under boost you should see close to 13volts. That 13v should be with the lights turned on, heater or a/c also turned on. The speculation is that running at night with the above items turned on....the voltage at the pump is in the dumps and hence not putting out its full potential....and possibly leaning out the mixture.

Have a go at it. Run at full boost and look at the voltage. Now do the same but turn all the lights/acc on and compare the figures.

It's a good idea to do a run like this up a steeeeeep grade so you put a REAL load on the engine. Not some downhill blast with hardly any load.

 

dude actually that sounds right man....mine usually runs like crap at night. and since im in tennessee i always have the bright lights on at night, my defroster or heater on full blast, and my rear defrost. alright im going to try that today..i have a DMM so it should be easy...thanks a million icemark

 

ok just got back from doing this test. found the connector clipped to the driver rear strut tower had a blue wire in it. shoved my red DMM lead into the blue wire and my black lead to ground. started the car, got 10.6v at idle, and around 10 with lights on heater on and rear defrost. but when i got into boost it didnt step the voltage up any! Granted i wasnt flooring it but i had the boost guage half way up and was accelerating hard and never saw it go up more than .02v. was i not pushing it hard enough or what?

 

Nope, does not take much boost to make it jump from 9 to 12-13 whatever volts.

Answer this: The Blue wire in the chassis plug...when you mate that plug to the fuel pump plug, is the wire that mates with the Blue wire on the pump plug a Black/White wire. It should be and probably is. Just wanted to know just in case.

If memory serves, and it will have to because I'm not near a diagram....there is on my 87tubo car a pin 3D on the ECU. That pin puts a ground on the fuel pump resistor relay, except when you go to boost the car. Then the ground is removed by the ECU and the relay relaxes and the path to the fuel pump does not have a resistor in it anymore.

Question: does your stock boost gauge work at all??????? That should tell me if the ECU is seeing boost from the boost/pressure sensor.

Off to watch FI on SPEEDVISION!

 

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The circuit works like the SERIES FIVE diagram above. Ignore the pinouts shown for the ECU.

On a series four, its pin 3D that is important. Here's what you do.......pull the small plug off the ECU. Then remove the wire from pin 3D and tape it and set it to the side. Reinstall the plug to the ECU and restart the car. The meter on the pump wire should now read battery voltage/alternator voltage of about 13.5v give or take.

To remove the wire.....pull the plug. Look at the mating end of the plug. With a very tiny, itty bitty small screwdriver or equivalant, insert the blade and pull down on the locking tab and extract the wire. Sorry, I can't describe it better than that.

The removal of the wire will tell you if its the relay or the ECU output that is keeping the 13v from showing up during boost.

This procedure works. I've done it a couple of times.

 

This jpg shows how 3D on the ECU will latch the relay in the fuel pump resistor relay package, and keep a full 13v from going to the fuel pump. When the relay is latched in, it pulls the contacts apart for the full voltage, and in the circuit goes thru the resistor resulting in a lower voltage..

 

why can't we just run 13volts all the time? just get rid of the resistor relay all together. just a thought, cause sometimes when i first start my car, i can hear the fuel pump spinnin like crazy and when i tap the gas, it switches to 9v and i can hear the relay switching. after a bit, it stays at 9v and i'm not sure whether or not it even goes to 12 after that, guess i need to check mine as well while driving.

 

my boost sensor and guage does work but it doesnt have the "pill". im not too good with wiring diagrams. i may have been doing this wrong i stuck my positive lead into a blue wire on the fuel pump side of the plug. im going to do a more extensive test monday. but if anyone knows how to get rid of the relay completely and run 13v all the time i would be interested. would it run rich at idle? i dont really care if it does just wondering?

 

i dont think that the injectors are too big, the only time that the car doesnt pull full tilt is about the first time i get on it or rev it above 5 grand...it will cut out for a minute then ill slow down....and run another 2nd gear pull and it will go till the redline...it seems that after the car gets warm, the secodaries blow just fine, like i said, the guy i bought it from said that there may be a problem with the voltage to the fuel pump and suggested i hard wire the power wire to a toggle switch to ensure that the pump was gettin the full 12 or 13 volts that is need to keep the fuel pressure high enough the blow the secondaries...the cosmos fuel pump should be plenty for just about any size injectors i believe...correct me if im wrong.. thanks for the feedback! its greatly appreciated

 

lYou stuck the meter lead into the wrong wire as you suspect. It's the BLUE wire on the chassis harness side of the plug that needs looking at.

I'm sure you noticed how the color of the wires change from one side of the plug to the other. The BLUE changes to BLACK/WHITE .........the black/white being on the fuel pump harness side.

On starting you get the full 12v. Once started it goes to 9 volts til you hit boost. Even a low boost will trigger the full voltage.

I just went and read your very first part of this thread.........NO. I don't think the fuel pump is the problem with your car. I just saw the part about the pump and responded to how you could tell if the pump was working as advertized. The sputtering could be that the engine is getting TOO MUCH FUEL instead of not enough fuel. I rank that as the most likely reason for your problem. But I'm just a guessing.

 

hey i went out and tried every other wire on both fuel pump and chassis side of the plug the only one i could even get close to 9 volts at idle was the blue chassis-side wire but it would never go from 10 - 13...WTF!!

 

IF the Blue wire never changes from nine to twelve/thirteen....then temp remove the wire from pin 3D of the ECU and start the engine. Even at idle you should see battery voltage with that pin 3D disconnected from the ECU.

If you don't feel confident on pulling a wire from the ECU...........get into the parts changing business and remove and replace the fuel pump resistor relay.

Or as an altenate.......back probe pin 3D with a meter. Put the meter on ohms. You should see a ground there. Now go for a ride. Boost the car. The ground should go away when in Boost.

OR.....cut the wire to pin 3D several inches from the ECU so you can splice it back together later. Start the engine. You should see 12v on the alternator even at idle now. This is not a power wire so your not going to short anything out or mess anything else up. Its only purpose in life is to put a ground on the fuel pump resistor relay so it'll put out only 9v when not at boost.

The color of the wire is BR or brown with a red stripe if you will. It's on the small plug on the ECU. With the plug connected up, and looking at the wire end of the plug, it'll be on the lower row.....second wire counting from the right. Brown/Red wire. Will not short out a thing when cut. Will not effect any other thing in any fashion. Bullet proof wire cut......just leave enough wire to splice the two parts back together if you decide to do so later. I prefer to just remove the wire with a tool like a stiff toothpick as I described in an above post.

 

so you are saying if i disconnect this wire i will get the full battery voltage to the fuel pump at all times?

 

Yes is the answer. That is a true fact of life. I recently depinned mine to prove to NXCONVERTIBLE something about the afr if the pump was/was not putting out 12v at idle. When disconnected...the voltage at the pump went to 13something volts(alternator voltage) and when the pin was installed it went back to the 9volts. The afr did indeed change from something like 13.2 to 12.9 (I don't remember the exact figures).

So I'm saying that if everything else is kosher and working....then the cutting or other removal of that wire from the circuit will result in battery/alternator voltage at the pump being at the pump when it's running. Not the 9v you see now. See the diagram I posted.