my car has a demon.

one day when i pulled out onto the highway my car stalled then backfired badly. i was able to drive it home at about 25 mph. anything above that and it would just stumble and backfire.

opinions seeded to think it was the fuel pump. i replaced that. while trying to set the fuel pressure we noticed when you turned the key on the prussure would jump up and the drop right back down. i drove the car home it started out ok but after about 10 minutes......it stalled and backfired but i was able to drive it home doing about 25mph, just the same as before.

next part....AFPR. i just got done putting it on and still have the same problem with the fuel pressure. even with the regulator adjusted as far IN as i could get it the pressure would only come up to about 40 psi and agian would drop right back down as soon as the fuel pump shuts down. i have not tried to start the car because i figure it will just do the same thing.

the engine only has about 15k on it. all the injectors, FPR etc. were changed when engine was installed.

oh ya, it's a 91 z with a vortec tpi engine.

anyone got any ideas?

 

sounds like leaky injectors

The Trickster!!!!!!!!!!!

 

hi tirx,


these have 15k on them, that sux big time.

anyway to determine which one is bad or does it matter?

could it be a short or something causing it to hang open?

if the injector(s) is/are bad, would that cause the other problems too?

 

The best place to start is the fuel pressure regulator. To check it, first install the fuel pressure gage on the fuel rail and then pinch off the fuel return line and turn the key to on. If the pressure holds, then you have a bad fuel pressure regulator(I went through three of them). If it doesn't hold, the next obvious step is the injectors. To see if you have a injector leaking take the plenum off and remove the 4 bolts holding the fuel rails to the manifold. Then lift the fuel rail so that the injectors are lifted above the manifold where the tips can be seen. Next have someone turn the key to the on position and observe the injectors to see if one is leaking. To answer your other question, yes it could cause your other problems because a leaking injector can cause an abundance of fuel in a cylinder and flood it out.

The Trickster!!!!!!!!

 

thanks trix........i swear that carb is looking better all the time!!

hey, i see you are from conway.....nice little town. you ever eat at Central Park?

ya, i know it aint a tech question.

 

Yep.

Been there, got a couple of automags that I shoot at the local range when they don't throw me off for scaring the other customers with the hand cannons. Started to ask if you were at Seymore Johnson until I read your profile. Yeah, I know this isn't a tech response :hail:

The Trickster!!!!!!!!!!

 

yep, they are leaky injectors OR you have a bad O-ring somewhere, i had the exact same problem with my car a while back, ended up being a bad injector O ring. Let the car prime and the look aroud all of the injectors for any fuel leaks.

 

ok...... another non tech respone.

gj on the auto mag. nice hunk of steel. you got the 44 or 357 version?

just tell the other customers to be glad it aint a barrett.

i spent 13 yrs in myrtle. we owned a small motel.

thats a no on seymore, i was born and raised here.
(Southern by the grace of ***)

by chance do you know jim ward?

i will get on the injectors tuesday....monday is booked.

 

Both in various barrel lengths with a .45 win. mag barrel thrown in for good measure. Also have to load my own. Definitely a non-tech response. :hail: :hail:

 

My friends 86 Z28 had a host of problems.
Wouldn't hold pressure at all after it primes or when you shut the car off. Car ran great once it started though.

His problems were 1 or 2 leaky injectors on the pass side, you could hear them leak when we turned the pump on manually.
Replaced the inectors.
Still had the problem holding pressure.
Changed AFPR
Still had the problem.
Cold Start Injector was leaking so we plugged the line at the back of the rail.
Problem was still there.
Changed Fuel pumps.
No change
Put my Holley pump on and problem was solved.

We found out the old and new AFPR were good, his old pump and new pump had bad check *****.
Now he's got a brand new fuel system.

 

all the stuff with the pump was replaced with the pump. is there anyway to know if that is the problem?

man, that carb is looking better and better.

 

Hey Slohand,

What have you been able to check on it so far and what were the results. Also, did I send you a copy of a fuel diagnostic chart that I have and if I didn't, would you like a copy. BTW, which did you want to borrow, my .44 automag or my .308

The Trickster!!!!!!!!!!!!!!!!!!

 

Wait a second...

The fuel pressure won't go over 40psi ever. And is erratic. And replacing the fuel pump has somehow not entered the equation why?

 

Obviously it has been done and it didn't correct his problem. Now he is looking to see what else could cause it and how to fix it.

The Trickster!!!!!!!!!!!!!

 

My bad. I guess i glazed over that part since all the symptoms still said that was it. Besides it's power, pretty hard to lose all that pressure. Unless you got a bad pump out of the box. The worst kind of problem to get...

 

How true Ed, been there and done that three times. Finally did it myself the last time along with my brother-in-law. Last sh*thead that did it put the **** wrong size o-ring around the sending unit and pinched it to boot. Had gas pouring all over the place when I filled the tank. And leaking injectors will give same problem. also remember, he put a adjustable fuel pressure regulator on and it will also cause the pressure to drop if it's leaking.

The Trickster!!!!!!!!!!!!!

 

ya, the pump was changed. when he went to adjust the pressure it would drop back down as soon as the pump shut off.

also, he could not get the car to run with the pressure under 40psi and had to adjust it to about 60psi to get it to stay running.

now, being the dumbazz i am.....i have looked in the repair manual and either don't know what i am looking at or it isn't labled as a fuel return line.

can you please educate me as to where it is located????????

trix....i still think you should get the barret.....my personal favorites are my original hk91 (new in 82) and my rem 700pss
i just love those 2in groups at 200yrds

 

Hey slohand,

Yeah, I wish I could get that Barret also. However, the wife said she would make me a deal. I buy her a brand new house with all the furnishings and I could buy the Barret. Well I'm still working on a new chair, does that count? Any way, there are two metal fuel lines coming off the tpi fuel rails that connect to two more metal fuel lines by way of rubber fuel lines. The larger of the two metal lines is the fuel pressure line. The smaller metal fuel line coming off the rail is the fuel return line. To check the fuel pressure regulator, you need to pinch off the rubber line on the fuel return line. Yeah, I love those very small grouping at two and three hundred also. I was on the Air Force rifle team at Myrtle Beach a good many years ago shooting a M-1 Garand.

The Trickster!!!!!!!!!!!!

 

rifle team? now im impressed. every get to camp perry?

lol on the chair. if you buy her the house you should get a ma duece and a hummer to mount it on.

thanks for the education on what im looking for. i will let you know what i find.

have a good nite!!

 

the plot thickens..........

ok, just went out and found the return line. had someone get in and turn the key on......0 read that zero fuel pressure.

i do have the plenum off but i can't see how that would make a difference.

i tried messing with the AFPR but no matter how far in or out i turned it i got zero fuel pressure. you can hear the pump come on and run but again.....zero fuel pressure.

i even pushed in the pressure release to see if maybe my new guage was broken and it will not pump any gas out of the pressure release line.

next i took off the fuel pressure guage and pushed in the on the schrader valve and i little gas started to come out and i relased it.

now what????

 

Hey Slohand,

You have e-mail!!!!!!!!!!!!

The Trickster!!!!!!!!!!!!!!!!

 

5SIZ!!!!!!!!!!!!!!!!!!!!!!!!

 

thanks for the info trix.....a gr8 help.

will email you about what i find.

now, pardon the HE double hockey stix outta me, but exactly what does that last post have to do with anything?

 

absolutly nothing, but us mods have to have fun to every once in a while. or else our heads will explode.

 

you were too late

 

finally!

ok i unplugged the fuel line where the rubber part is. almost no gas came out when i unbolted it. next i turned on the key and it pumped out about 2-3 ounces rather quickly then 'clicked' off. i tired this 3 times and got the same result each time.

is this correct?

 

Yep

Will send more later.

The Trickster!!!!!!!!!!!

 

You probabley have a bad pulsator. When you replaced the fuel pump was there a plastic thing between the pump and the supply line? If so they are notorious for leaking, replace it with high pressure fuel line and all will be well.

 

Like sands through the hour glass.....$650 and still not done.

ok, new injectors, new tps, new AFPR and still have same problem.

i finished the car this evening. cranked it, set the fuel pressure. checked for leaks etc. and the took the car out. i drove about 2 miles and then stopped for gas. the car felt pretty good but i took it easy. after filling it with gas i head for the on ramp to get up on the highway. after i accelerate up the ramp i pull out to pass and feel the car start to stumble so i back off the gas and pull back in.

i coast up to the exit and as i am pulling off i give it some gas and the engine stubles and misfires.

the 'better' part is it let me dreive 35 to get home instead of 20 and it did not backfire. anything above 35 and it just misfires.

this seems to be tempeture related, although it only got to about 150 before it stumbled.

anyone wanna take a stab? or a gun shot? or a bomb? nuclear?

 

update time.......

i wish i had better news.

replaced the throttle position sensor suspecting a malfunction there. NO luck. after about 10 minutes of run time at about 150 degree temp. the car starts missing like crazy again and it is back to the 25 mph trip home.

 

add to the list of replacements a new mat sensor as well.

 

Hook your fuel pressure guage up. Turn the key to run. Does your fuel pressure still go up to around 40psi then drop down around 0psi?

 

Man, I hope you have some better luck soon. I had the exact same problem, but I put some accell injectors in and problem was solved. Good luck man!!

 

'better luck'...lol... i think i am goin to need more than luck.

i bought a holley at the suggestion of someone on the board. the first one i put on, the fuel pressure would go up and then slowly go back down to 0 but it took about 8-10 seconds. thinking it was bad i bought another and it did the same thing. after checking with a 'tech' it seems it is designed to do this. i am guessing as a safety measure. with the car running it is set at about 42 because of the 24lb injectors. i can't keep the car running right long enough to see if this is the best pressure.

again, this problem seems temp. related. after cranking the car runs ok until it gets to about 150 degrees. i have also noted that the higher the temp the worse it is when it goes.

does anyone know it the 'mis-fires' are normal in limp home mode?

 

I'm wondering if you have a bad coolant temperature sensor (CTS) since it's starting to become temp related. With a misreading CTS, it may be telling the ECU it's up to -42 degrees outside. ECU tells the injectors to flow fuel like crazy at those temps... I hate combined problems like this... Good luck man!

Get a scanner of some type running. It's better than throwing money at it again. Plus, next time you will have the scanner to avoid throwing more money at it...

 

thanks for the input.

i have been looking at scanners but am not sure which one to get,
suggestion?

there are many for sale on ebay and i was considering purchasing one there.

i may just go get a cts and try it. maybe that 'luck' i have been waiting on will arrive.

 

I have heard alot of people having problems with the cts!! It might be a good shot, you never know. I would definetly get a scanner for that thing.

 

CTS is on and still have same problem. car runs fine til about 150-160 degrees and then it will not run above 25-30 mph which i think is the 'limp home mode'.

also i noticed on one of my other posts i said i put on a MAT it was actually a MAP.

suggestions on the next sensor etc?

even though i don't have the solution yet all your input has been appreciated.

a special thanks to you Trixter!!

keep the ideas comming please

 

now for the news........

add a MAT sensor to the list of new stuff.

also note it will take at least one more piece of new stuff.

anyone? anyone at all?

 

Did that include the pulsation damper? If not, you may have fuel leakage inside the tank. Even if the pulsation damper was replaced or eliminated with a section of hose, you may have leakage inside the tank. That can include damage to the steel lines as well.

I fought this one for quite a while on a Fiero, even starting and driving it for several days while trying to diagnose the mysteriously variable fuel pressure. I finally discoverd the problem - this is the way it came out of the tank:



As for the CTS, TPS, MAT, O² (pick one or all), none of the engine sensors will affect fuel pressure, and until you solve that problem, you can replace components endlessly with no improvement (unless you own stock in the parts company). Get back in focus, and get the system to maintain fuel pressure. Since you have the plenum off, it will be easy to remove the fuel supply line and test the pressure right at the line, with NO injectors and fuel rails connected. You could also do the same thing at the fuel filter if you have the filter pressure test adapter.

 

yes, pulsator damper was replaced.
fuel pressure stays at a constant 42psi with the car running. the drop only occurs with the car off when the pump is priming. it goes up to about 35psi and the slowly drops back. now it only does this with the holley.

the other AFPR (jet)holds pressure.
i was told that the holley was designed to release pressure.
i have bought 2 of the holleys and they both do the same thing. after the pump primes it allow fuel to run down the return line. like i said the other reg. holds pressure so i figure the guy who told me the holley was designed that was was correct.

oh ya, the car is back together but will come apart as needed.

thanks you for replying!! mighty Vader

 

oops!!!!!!!!!!!

Hey Slohand,

Thought you was going to hot Atlanta for a day or so. What happened!!!!!!!!!!

 

hi trix,

i'm off to atlanta, running late as usual. i will check the board when i return.

stay fast!! and get the dang leak fixed : D

 

Have you tried to monitor the fuel pump voltage during the prime cycle? The pump gets voltage through the FP relay during prime, and via a redundant path through the auxilliary oil pressure switch once the engine is running. Pumps can be very voltage sensitive, and your low pressure during prime could indicate a low voltage due to resistance in the FP relay and its circuit.

If I'm reading your information correctly, it seems that the pump is producing adequate pressure while running, but does it still drop quickly after shut down, or does it now maintain pressure with the new regulator?

 

Hey Slohand,

Got the leak fixed, washed and shined the car, spread about a ton of gravel in the driveway. Hot, tired, wanting a cold one, and the wife decides that I have to take her out for dinner

 

Hmm, I know for a fact that my fuel pump is fine (Tested fuel pressure), but when I prime the system before startup, it will only prime the system 15-20 psi?

Would replacing the relay help?

 

Did you buy a "master" brand pump by any chance (sold at autozone) ?

I've replaced 3-4 of these in a 1 week period on some cars. Sure they take 'em back, and chuckle. The alternative is buying the real pump (ac-delco) or a performance pump such as walbro, or holley.

I'm not joking. Don't believe me, call autozone and ask them how many "master" pumps go bad.

While your at it, ask them about their "valuecraft' 19 dollar alternators.

-- Joe

 

ok, im back. not bad 6 hours from gboro to atl. in an suv. i love my valentine I.


starting from the time i get in the car and turn the ignition on. this is with the new holley (second one, first one does same thing)

by turning the key without starting the car the pressure goes up to about 36-38psi and then starts dropping slowly back down.

if i start the car the pressure hold perfectly steady at about 40-42psi which is were i have the regulator set with 24lb injectors.

again, the car runs fine until it gets to about 150 degrees and then the system just goes screwy.

i have not tested pressure after shut down or the voltage. again this only develops the problem after the car has been running and the tempreture hits about 150 degrees. if the test needs to be done i will get it done.

the fuel pump was ac delco. i learned my lesson with 3 new 'gold' alternators from auto zoned in 2 weeks.

Trix,

good job on the car and good job on the drive way. sounds like your wife still need training.

i'll send you a pic of how a wife should greet her man when he gets home.

 

this may be a long shot by did you try the o2 sensor maybe its telling the computer your running lean and its keeps adding fuel not sure if the o2 gets hot by that time though

 

the o2 sensor has about 10k on it.

i became convinced it was doing this when it went into closed loop so i unhooked the o2 sensor and it did the same thing at the same temp.