i have been dealing with a real bad missing/stumbling problem for awhile now and today i checked the resistance on the inj. they were all 16.2 ohms which i beleive is ok. heres the prob, as soon as i cut the car off the fuel pressure drops to zero IMMEDIATELY, even when i pinch off the return. im am guessing this means that one or more of the injectors is hung wide open. fuel pressure is 38 with vacuum on and 45 with it off. would a wide open inj. cause a real bad idle and bucking and sometimes stalling prob? its seems like it is running super rich. i am at whits end with this tpi. are there any other test i can do to make positivley sure that i need to replace the inj? at low speed sometimes it bucks and runs crappy and sometimes it doesnt. when i am out on the road it seems to run pretty well, that is why i am stumped. any help is appreciated. i was dead set on a carb and my buddy talked me out of it, but this tpi is just so nerve wrecking. thanks in advance!!!

 

cmon guys

 

im having exact problem--sept mine wont start now! getting a code 34 too--im switching to carb, tpi is just to damn expensive and hard to diagnose.........

 

im >< this close to doing the same thing. too many variables when trying to track down a problem. please let me know how you like the carb.

 

well if you successfully pinched off the return line and you still lost pressure real fast then yes there is a fuel leak somewhere. Do you smell gas anywhere? what kind of FP gauge did you use for this test? have you checked for fuel leaks under the car or at any of the connections?

 

Could be the fuel pump. There is a diaphram or something in there that can come apart.
My friend was just talking about fuel pressure dropping just the other day and this happened a few years back on his 95 Z.

 

i have verified the fp on 2 seperate guages, and they both read the exact same. what is the diaphram in the pump you are talking about? would it allow fuel pressure to still bleed that fast with the return line pinched? when my car idles real bad like it has a dead cylinder the fuel pressure stays perfect. prob just getting more fuel than it can burn and flooding a cylinder. you guys know how to check the harness to make sure the prob isnt electrical related before i order my injectors and tear the car down? any help is appreciated and any test you know of would help a bunch.. thanks in advance!!!

 

The diapghram or should I say check valve, can become defective and allow the fuel to run back through the pump into the tank.
If you could hook up a fuel pressure gauge to the feed line on the body of the car, that would allow you to test the pump exclusively.

 

i pinched off the return while the car was running and i got about 84psi on the fp guage. i am not sure if that is what you mean though

 

No, what I mean is disconnect the feed line from the fuel rail and attach the fuel gauge to the feed line.
You are basically going from the tank to the pump to the fuel gauge. Turn the ignition on to prime the pump and watch the gauge. If it loses pressure right away, then it's a bad pump.

 

cool man , i will check it out. thanks

 

Ya, let me know what you find out.

 

well today i rigged up some fittings and unhooked the 3/8 feed line and hooked up my guage.... relay primes pump for 2 seconds then clicks off...fuel pressure goes up to around 80psi and then back to zero immediately. so...now that you are officially my hero.. what sort of drivability probs could a bad check valve do to my car? i mean when the car is running and even when its stumbling like it wants to die the fuel pressure stays steady at 38 with vaccum and 45 without. i am so confused on this problem. the car is my daily driver and it seems to do decent most of the time but sometimes it gets real nasty and doesnt even want to idle at all. i can feel misses while driving most of the time. would a bad check valve cause any of this???thanks for your help man i really appreciate it!!!!

 

Replace the pump and thank yourself later.


(cut the hole. )

 

do you think the pump is causing all my probs???

 

Yep, replace the pump and you will have no more problems.
Sounds like it's on it's last leg.
Walbro is the one I'd get, everyone I know has one.
Also change the fuel filter as well.

 

man you are a lifesaver!!!!!!!

 

Just helping out a fellow thirdgenner.
It's funny how I got this info about the pumps a few days before you posted. Strange coincidence, eh.

 

lol... that is ironic..but i do appreciate the help man...till next time later man

 

Anytime.

Later.

 

hey 1 more question...what purpose does the check valve have after startup and how could it cause my bucking stumbling prob?? thanks again man!!!

 

I am not sure what the purpose is after it is started, but the bucking/stumbling could just be a sign of a bad pump or it could be from the bad check valve.

 

Bad check valve won't cause any driveability problems, just a little bit longer crank times since the fuel system must be primed each time you start it.
If all of the injectors ohmed the same then it is safe to assume (for now) that they are not leaking.
To further the troubleshooting, replace the pump and see if it is causing the problem, if it doesn't cure it you'll at least know the pump is good and the longer crank times should be a thing of the past.
Replace the parts you know are bad and keep pressing on with the troubleshooting.

 

The purpose of the diaphram in the fuel pump is to act as a check valve. It keeps the fuel from draining back into the tank, thus keeping your fuel pressure and making it easier to start next time. I did not know that the bad check valve would cause the pressure to shot up to 80 psi though. I would still check out the pressure regulator. Just me though.

Mark

 

He was crimping off the return line when he got 80 psi, deadhead pressure, which is what it should read at that time.

 

i am going to buy a noid light and check and make sure my injectors arent shorting out or something. they were sent to cruzin 24k miles ago. this prob has been driving me nuts!!!!

 

Change the pump first since we know it isn't functioning right and see if you still have drivability problems.

 

first i am going to pull the plugs and see what they look like. then i am gonna check with noid, and then its pump time

 

I like using in-line pumps. Most people aren't fond of them, but I like the aspect of changing the pump in a matter of minutes instead of hours. Also makes upgrading easier.

 

what about the existing pump in the tank?? what all is neccesary with that type of install? definately something to consider!!

 

Unfortunatlely, you will have to remove it and mod your current intank setup by adding a rubber hose inplace of the intank pump.
I had a carbed car so I had no intank pump to mess with.
Or you can get the intank pickup from a carbed car. I have one here that I am selling and it has a working fuel level sender on it.

Since you have to pull yours out, I'd just go with the Walbro since it should last 10 times longer than in in-line one.
Estimated life on an in-line pump is 2500 hours. In-tank ones last about 25000 hours.

 

well i finally got off my lazy *** and replaced the pump. i just used the ac delco ep-241. i hooked my fp guage up to the supply, primed the pump and fp shot right back down to zero. wtf is going on here. my pump acts like it doesnt even want to prime all the way up, like it is lazy. when the car is running the pressure stays just fine. should my car be able to start with out the fuel pump relay hooked up? i read about a oil pressure switch is why i ask. because my car will not start without the relay hooked up. does the relay have any purpose after the pump is primed? could a dying relay cause my fuel pressure not to come up like its supposed to when its primed? it took like 3 cycles to come up just to 65 psi from the pump directly. somehow this is al tied in to a bad surging prob that happens ever so often. but usaully after the car is hot. a buddy put the car on his scanner and the only thing out of spec was the o2 sensor. it was staying like 950 then jumping up to 1300 he said. i dont know exactly because i wasnt there. i replaced the o2 today and it seemed like it really didnt help that much. for the most part it just runs kinda rough at idle and sometimes, like maybe once a week goes into total wtf mode. i can hold the pedal like half throttle and it just cuts out horribly, but most of the time only after i have driven it and get back in it to leave. always runs good the first time i drive for the day. i have been dealing with this shyt ever since my cat went soth and i replaced it with a straight pipe. also sometimes the starter just clicks, sometimes it spins nice and fast , and sometimes it just seems to be slowly turning. i dont know if that has anything to do with anything, but it seems to start alot fatser when the starter turns real fast. also when the pressure doesnt build upon me priming the system, the pressure will shoot to 40psi after several turns of the motor. what could this crazy prob be? i am so sick of this shyt it is unreal. i have been stumped for months. every sensor has 24k miles on it. except o2. new fuel pump, tune up 3k miles ago. any help is greatly appreciated, this is my daily driver and i want to get it running right without having to worry about it.

 

You're pig-rich. I saw it mentioned above...possibly injector(s).

Ohm reading only tells you the injectors ability to electrically operate...not mechanically operate.

Have you pulled the plugs? Look for a rich running cylinder or two, or three

 

what exactly would the plug look like if the cylinder was running rich? tommorow after work i will pull the plugs and see. should i buy a noid light to test the injectors? i never got around to doing that. all i did was placed the tip of a long screwdriver on each injector to see if they were all firing and they were. thanks for the advice man

 

Prime the pump a couple of times then pull the plugs, any leaking injectors will coat the plug in gas and the plug will smell strongly of gas.

Forget the noid light (for now) if you could hear the injectors firing with the screw driver

 

well i didnt get a chance to pull the plugs because my friend has my jack. but, i did do a different fuel pressure test. i started the car and pinched of the return...pressure stayed at about 80-85psi, then i got a buddy to cut the car off while i pinched the supply....ah ha... fuel pressure held at 40psi...so i released the return and the pressure still held...released the supply...pressure dropped to zero immediately. wtf is going on here? i am guessing my injectors are fine since the pressure didnt bleed when i pinched both lines off. does anyone know what could be causing this? i am ready to take my car to a dealer. this all ties in to the surging (sometimes) but running rough all the time and stalling sometimes when it surges. the iac motor tries its best to keep the motor running but after 20 seconds or so it just stalls, but that usually doesnt happen alot. maybe twice a week. but i dont really put alot of miles on it since i only live 3 and a half miles from work, and its backroad driving, no city. any help is appreciated, i am at whits end with this thing. also, the surging porbs and stuff only happen on startup, never happens after i am out cruising and i stop at a light or something. most of the time it happens after i go somewhere and get back in my car to leave, sometimes it just acts crazy. but i can make it act better if i get on it and run it hard. it just seems to clear all up. i dunno, im totally mindboggled by this one.

 

It's either the pump checkvalve (replace pump) or the pulsator between the pump and feed line (in the tank) has split. Going to have to drop the tank and check it out. If you drop the tank and the pulsator is bad, just replace it with a piece of fuel hose rated for fuel injection. And I'd replace the pump and strainer at that time too since the tank is already out.

 

i replaced the pump last weekend. would any of this fuel issue cause my other probs to? also takes like 3 primes to bring the pressure up to 40 on my guage.

 

Yes, if there are no external leaks then the pump is most likely at fault. If it takes 3 primes to get the pressure up then the pump is no good or the filter is all but completely blocked.

 

it took that long before i changed pumps. the pump swap didnt help at all. any more suggestions? i changed the filter about 1500 miles ago so i wouldnt think that would be it. figure this shyt out and i will gladly send you a 50 dollar reward. i am totally stumped.

 

did you inspect the pulsator between the pump and the line i had a hole in mine and didn't notice it when i changed my pump my press would not get above 10 pounds

 

looked fine, the press stays dead on with the car running, even when it goes into phsyco mode

 

The pressure may be fine but you are probably loosing volume. The fuel system should hold pressure with th pump off and yours isn't. You have laready narrowed it down to something in the tank, be it the pump or pulsator, there is a problem.

 

i replaced the pump and the pulsator last weekend.

 

anyone have a clue??

 

This says there is something in your tank letting pressure out. So, unless you have a ruptured line from the tank to the engine, its time to drop the tank again.

 

thanks man, i will check it out and let you know what i find.