I've noticed that my fuel pump has been cycling longer than normal lately. I'd say over 5 seconds or so. Is this normal? I thought I read on here one time that there was a relay or pulsator or something that could go bad and cause this? My car also has been stumbling on hard acceleration SOMETIMES(almost acts like a slipping clutch, but no rise in rpm's) and runs GREAT other times. Bad fuel pump? I still need to test fuel press and WOT fuel press. Any preconceptions though? Thanks!!!

------------------
'91 GTA:5.0TPI-5-spd, Hypertech Stage 2 chip, 160stat,!TB,!Cat, K&N, Flowmaster muffler, Accel Coil,TPI Air Foil, 1LE Alum DS, poly-tranny mount, KYB's all around, & a Hotchkis Strut tower brace.
Mods in progress:
-L98 w/ZZ4 cam/springs
-Edelbrock headers
-3" flow setup
Future:
-T56/heavier clutch
-Hurst or Ripper
-4.10's
-Ram Air II Hood
-1.5" Springs
-Rebuild suspension!
Others:
-39 Chevy coupe
350/350/3.55posi
-52 Chevy p/u
-77 Bonneville 400PONTIAC/400turbo/posi
Original 50k mile 2 door... Gramp's old car!
*** Gotta love those Poncho's***

 

We had a discussion about a few months ago. The discussion should be in the archives somewhere. The general concensus was the cycling was a result of extremely cold days. The fuel pump cycles the fuel to "warm" the fuel for better atomization and quicker start ups. My old pump did this and my new walbro, even my '95 'vette "cycles" especially now since it is like 0 degrees here in NJ.

 

Attention...There was never a fuel system on any gm car that cycled the fuel to warm it.The pump on a TPI car is turned on by the computer via a relay at start up and after start up there is a oil pressure switch that closes and completes a circuit that supplies contsant power to the fuel pump until the engine is shut down and oil pressure is low.THE FREAKIN FUEL PUMP DOES NOT CYCLE ....Now to really blow your minds the reason the fuel is circulated all the time(while the engine is running) through the fuel rail and tank is to COOL IT !!<fuel>

------------------
87GTA,350,Auto,MAF screens removed,195 thermostat,cold start injector UNPLUGED,K&N,modified air intake,ADSchip,3:70s,3inch cat back Flowmaster single outlet,TPS.54,Bosch Plat plugs,base timing 6BTDC,22 MPG,what a ROACH,Bilstiens in the rear....,don't let yer meat loaf

[This message has been edited by RP1987GTA (edited December 27, 2000).]

 

RP1987GTA-
OK, but why is my pump still running after I shut my car off. Its not cycling??????? Then what the he** is going on. It is REALLY cold here(about 0-10) like the other guy mentioned. Oh well, thanks for the help and hope to hear more.

 

Ok here is your answer :your oil is thick when its cold,so it takes longer to drain off the oil gallery,hence the oil presure switch supplies power to the fuel pump until the oil pressure is low.So when you turn the engine off there is still enough oil pres. to hold the switch closed for a few seconds.Let me guess your using 20/50?

 

You're the **** man! I guess I can't say that though. I am running 20w50, but with a little others too(my car is burning or leaking a little) and its on the way out so I don't worry much about my oil, but I have been using 20w50. I guess thats why, and YOU'RE right. Its been really cold here so I guess the oil has been even thicker lately. My motor still runs awesome oil pressure, even b4 the 20w50. Oh well, guess I have no worries then. What do you think about the stumbling though? Check fuel pressure? Change fuel filter? I don't think its my clutch just because when it stumbles/slips, there is NOT a rise in my rpm's(aka slipping clutch). Thats why I think it may be a fuel system prob. What yay think? ANyone else? THX!!!

------------------
'91 GTA:5.0TPI-5-spd, Hypertech Stage 2 chip, 160stat,!TB,!Cat, K&N, Flowmaster muffler, Accel Coil,TPI Air Foil, 1LE Alum DS, poly-tranny mount, KYB's all around, & a Hotchkis Strut tower brace.
Mods in progress:
-L98 w/ZZ4 cam/springs
-Edelbrock headers
-3" flow setup
Future:
-T56/heavier clutch
-Hurst or Ripper
-4.10's
-Ram Air II Hood
-1.5" Springs
-Rebuild suspension!
Others:
-39 Chevy coupe
350/350/3.55posi
-52 Chevy p/u
-77 Bonneville 400PONTIAC/400turbo/posi
Original 50k mile 2 door... Gramp's old car!
*** Gotta love those Poncho's***

 

RT, Please read thoroughly before the sarcasm, the purpose of these boards are to clearify why, not criticize. The shutdown sounds good but the oil sending unit does not turn off the fuel pump regardless of oil pressure (big misconception), the oil sending unit is a back up if the fuel pump relay fails (at least my service manual says that). let me be more specific, the pre-morning start up, that is what I am attempting to resolve.

In the morning on extremely cold days ONLY , first start up, both the vette and camaro, the pump cycles for more than 3 seconds, sometimes up to ten (10) seconds, can you explain this? Oh yeah the Ford does it even longer in the morning. Why, Explain the morning pre-startup "cycling"?


[This message has been edited by blak92! (edited December 29, 2000).]

 

GTA91
-------
Your stumbling is most likely caused by your TPS (Throttle Position Sensor)!! Check the TPS, if you need to know how look in a Chiltons or Haynes manual! I believe there is also an article on thirdgen here that explains how to check it! The voltage to the TPS is supposed to stay the same as you incerease throttle but when the TPS is going out, the voltage will jump with acceleration causing a "stumbling"!! Check it out!

------------------
1986 Trans AM
305 TPI
Completely Stock
Soon to upgrade to a 327 TPI with pocket ported 64CC heads, comp cam, TPI air foil, Adjustable Fuel Pressure Regulator, possibly bigger injectors!
Current project: Installing an Accel Inline Fuel Pump since I've been through 3 Fuel Pumps in 2 Years! :-(

 

Yes and no....the fuel pump relay will be energized as long as the key is on...the oil pressure switch you're referring to provides an alternate (parallel) path for voltage to the fuel pump...losing oil pressure will not shut the fuel pump off...unless the FP relay is not operating.

The purpose of the oil pressure bypass switch is to provide the fuel pump with voltage in case the ECM driver (quad dricer I believe) or FP relay goes south.

 

8mike9 yer totally lost!!!!the ECM is the ONLY thing that can turn that fuel relay on...enough said ...i'm done with this thread too many my friend told me this or ...the guy turns his key on in the morn and doesn't start the car right away.....ECM primes the fuel rail <3-5 sec run time>then if you don't crank it over ....ECM does not enable the fuel relay until it gets the signal from the ing.module....if the fuel relay is bad or ECM output driver is fried cranking the engine over until aprox 8 psi oil pres is reached will bypass the fuel relay sending 12vdc directly to the pump until oil pres. is no longer...bye bye daddy ...bye bye mommy

 

No, I'm not lost...

What you have written above, is correct, but what you wrote before, is incorrect...unless I read it wrong...

You're stating that if I'm tooling down the road, lose oil pressure...my fuel pump will shut off?

Me don't think's so...but I'd better run and ask my mom to be sure....er. maybe dad will know.

[This message has been edited by 8Mike9 (edited December 29, 2000).]

 

LOL,

I am with you 8Mike9. The oil sending unit will not prevent you form blowing the engine if you lose all oil pressure.
I guess my service manual must be wrong RP1987!

Mike, Any clue about the extra priming on extremely cold days?


------------------------
92 Z28 350 5 Speed
95 Competition Yellow Corvette 6 Speed

[This message has been edited by blak92! (edited December 29, 2000).]

 

OK guys, so which is it? Checl my fuel pump? Check my feul pump relay? Check what??????

*Also- Does anyone else think it could be my TPS causing the stumbling? When it does the stumbling, ALL motor power goes down. Its like it hits a huge brick wall until you let off or it stumbles on through. Usually I let off because it feels so bad. What is going on? I really don't want to replace a fuel pump if not necessary.
THANKS FOR THE HELP EVERYONE!

 

If you haven't adjusted your tps lately you need to do it anyway so start there. Follow the procedures in the tech section and make sure the voltage increases smoothly as you open the throttle (use a regular, not digital, voltmeter for that part).

I have always understood that if you're going down the road and lose all oil pressure your fuel pump will cut off. This is in case you have a wreck your fuel pump won't keep pumping gas all over your carcass!



------------------
87 IROC-Z, 5.7, auto, 3.27, leather, !cat, Holley fpr, K&N'S, SLP 1-3/4" Jet-Hot coated headers, SLP .218/.224 .495/.502 cam, Comp 1.5 roller tip rockers, $uperPITAram, Edelbrock lower intake, Holley 52mm tb, Dynomax\Flowmaster catback. Coming Soon(?)- Fasttrack/Accell DFI

1989 Pontiac 20th Anniversary Turbo Trans Am - 161,000 miles, !cat, 9" K&N

 

Brain fart message...

[This message has been edited by 8Mike9 (edited December 30, 2000).]

 

What a total brain fart I had...hope noone had a chance to read it before I wiped it out...

How cold are we talking here? I know in the winter when I've been in the 20's in my car, it still only primes for the 2 second duration...

ONe thing the think about, and I'm only tossing around an idea here, is that we know the ECM energizes the FP relay for 2 seconds...now it's possible that this "two second" time is via a timer, preset and nothing you can do about it...or...it could be that the ECM monitors the FP voltage for the "prime time" (not Deon), and if that's so, it could be possible that when really cold, you may have lower voltage that the ECM does not in terpet as a prime signal...not as I mentioned before, purely conjecture because I'm not sure if the voltage is sent via a tiumer...or timed via feedback through the realy to the ECM (where the ECM monitors for high/low FP voltage).

I'll try to locate my manual and see if it goes into this...may take a day or so for me to find it..it's packed away right now.

 

I've noticed that on my TTA when it's really cold sometimes the fp will keep running if I turn the key on the back off w/o cranking it. I have to cycle the key a couple of times before it will stop running. Could the relay be "sticking" due to the cold weather?



------------------
87 IROC-Z, 5.7, auto, 3.27, leather, !cat, Holley fpr, K&N'S, SLP 1-3/4" Jet-Hot coated headers, SLP .218/.224 .495/.502 cam, Comp 1.5 roller tip rockers, $uperPITAram, Edelbrock lower intake, Holley 52mm tb, Dynomax\Flowmaster catback. Coming Soon(?)- Fasttrack/Accell DFI

1989 Pontiac 20th Anniversary Turbo Trans Am - 161,000 miles, !cat, 9" K&N

 

better ck under yer constabulator for frozen electrons,an old woman down the street with a 72 nova told me she has the same trouble.

------------------
87GTA,350,Auto,MAF screens removed,195 thermostat,cold start injector UNPLUGED,K&N,modified air intake,ADSchip,3:70s,3inch cat back Flowmaster single outlet,TPS.54,Bosch Plat plugs,base timing 6BTDC,22 MPG,what a ROACH,Bilstiens in the rear....,don't let yer meat loaf