My 86GT has been running rough and has been hard to start for a month or so now. The only thing that seems to help is if it is at running temp. Until then the symptoms are very noticeable. It bucks and hesitates when accelerating but has enough power to maintain speed once you get it up there. I did a couple of things like change the fuel filter/cap/rotor/wires/plugs and ign module and then I finally checked the fuel pressure. (note that the filter had lots of silt on the inlet side, explained below) It will only prime to 20 psi and when the engine starts it jumps to 32 psi. Obviously the cause of my problems. This has been verified with two different pressure gauges so at least I am comfortable that the readings are correct. I do not have a means to watch the fuel pressure gauge while driving so these readings are with the car in Park. If I rev the engine, the fuel pressure drops momentarily to about 28 psi and comes right back up to 32 psi. I did not have a way to unplug the vacuum line from the fuel pressure regulator without unplugging the vacuum from the map sensor so I don't know what the effects of removing vacuum while the engine is running are. I did check all the vacuum lines and they are not leaking.

I checked the fuel pressure several years ago and it was 43 psi at that time.

The reason for suspecting the fuel pump is that when I got the car, the fuel pump was inop. This was because the car had sat for several years and the tank corroded fouling the strainer and clogging the pump. I only rinsed out the tank and replaced the pump. I did not do anything to prevent the corrosion from spreading. Along with that, I threw away the fuel pulsator dampener thingy that connects the pump to the supply line and replaced it with the short piece of fuel line that comes with the pump. So, I believe that there is a strong possibility that the short fuel line could have ruptured or the tank continues to corrode either of which could cause problems.

The only reason I suspect that the regulator could be a problem is that the pressure holds steady at 20 psi when primed and 32 psi idling and when the engine is revved the pressure only drops a little and then pops right back to 32 psi without going over.

Any thoughts?

Charlie

I had simmilar problems once....I 'think' my fiero must have been sitting sometime in the past because when I got fuel and starting problems I found a lot of rust debris in the filter and rusted metal fuellines (inside) , also after the filter...Then I found the injector inlets were full with rust particles. Rust may also jam the regulator..
When I replaced the fuelfilter and having the injectors cleaned/rebuild/tested it ran fine again
Not to say this is your case...but a thought
good luck !

Thanks for the ideas. I guess I had better buy a new fuel regulator and get ready to install it. If that does not fix it, then I will buy one of those corvette pumps recommended for the 3800 swaps and install it while the tank is down for inspection/cleaning.

Charlie

You may want to double check the vacume line that goes to
the fuel pressure regulator. It also goes to the MAP sensor. If
there is any leak in that line it will cause low fuel pressure along
with the MAP sensor not getting the right air pressure.

If it only gives you problems when its cold it could be you also have an o2 sensor issue. These cars use unheated sensors and thus can be bit of a PIA when cold espeacally when dirty. We recommend to our header customers to switch over to heated o2 sensors, whereas our headers lower the exhaust temp.

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quote Originally posted by Larry Nakamura: You may want to double check the vacume line that goes to the fuel pressure regulator. It also goes to the MAP sensor. If there is any leak in that line it will cause low fuel pressure along with the MAP sensor not getting the right air pressure.

Thanks for the thought. I checked it along with every other hard plastic vacuum line and to my surprise, none of them were leaking. The only other thing I need to check is the egr tube going up to the plenum. I put a brand new one on a couple of years ago so I want to see if it is still ok. Since I will be taking the plenum off soon to replace the regulator, I can check it then.

Charlie

When thinking about the fuel system don't forget to
include the overflow can (under passenger wheel well),
and the vapor canistor (has vacume lines too). Just
something to think about when trying to trouble shoot
fuel/pressure problems.

I have decided to drop the fuel tank first and see what kind of shape it is in. Yesterday I ordered one of the 255LPH TREPerformane pumps to replace the stock pump. I am assuming that the foriegn material in the tank has clogged the strainer and or the pump.

Charlie

any update on this?
im having very similair problems with my fiero
i still havent got a pressure gauge >.> I will be getting one this week

was the problem with the fuel pump or with the regulator?

the reason i ask is that i suspect something wrong with my regulator
there have been several times that the car will stall out and when i press the shrader valve air comes out
i cant see how the puel pump would be pumping or allowing air in and the only thing that makes sense to me is the regulator could be out
the car did sit for a while before i got it and has been sitting off and on since i got it

im going to hopefully get it inspected tomorrow and hopefully start diagnosing the issue again
my truck died on me this weekend so i am having to repair the fiero sooner than i was planning
hoped to sell the truck and fix the car, now it looks like ive gotta fix the car, then the truck and decide what to do later, lol

updates!! need em

I bought one of those cheapy Harbor Freight testers for $15. It works well enough for the few times you need it. You might consider a gauge bolted to the schrader valve too.

im on my way to harbor freight right now

Download and read the manual as to what pressure readings you shoudl get. The pressure IS supposed to vairy according to the intake manifold pressure.

The problem you are having sounds like a weak fuel pump. If you recall times ago, that people would get "vapor lock" on their cars because the fuel in the fuel lines evaporated into a gas. I am thinking that is what you are getting.

The reason most all Fiero owners don't get this is because the fuel pump will pump fuel to above 40 psi, but the fuel regulator will return excess pressure to the tank. If the fuel pump becomes less than enough to get to the 40 psi the regulator never opens at all and no fuel is returned to the tank. At times if the fuel line gets warm enough the fuel evaporates inside the lines but since(if) your fuel pump is weak, no fuel/vapor is returned and you have a no-start situation.

So my expectations is that you will find your fuel pressure low, but enough to get the engine to run usually. If the fuel pressure gauge reads low, the test to see if it is the regulator or not is to squeeze the rubber part of the return line with a vice grips. If that makes the fuel pressure increase to above 40, then your regulator is bad. If the pressure is still below 40, then you have most likely a bad fuel pump, or maybe a bad filter, or bad rubber hose from the fuel pump to the metal line leaving the gas tank.

[This message has been edited by phonedawgz (edited 06-07-2010).]

what youre saying sounds right for me phonedawgz
i havent hooked up the pressure gauge yet, its freakin hot outside

my problem happened again today, it holds pressure but its all air or possibly evaporated fuel
press the shrader valve when the car wont start and i get a loud high pressure his of air/vapor
turn the key off and on a few times and hit the valve til fuel comes out and she starts and runs with very little problem

once the sun goes down im going to go back out there and take some pressure readings but from whats happening and what youve said it sounds like a weak fuel pump as youve said
she is going in the shop tomorrow to get the ball joints replaced so i will find out how much they want to evaluate the issue and possibly replace the fuel pump if they agree thats the issue

i hate working on cars in summer in texas, lol

for now ive got a temp solution to keep me on the road with bleeding the fuel lines of air when she wont start

I've got a wood stove in my garage plus a ceiling fan to circulate the air so my feet don't get cold. We're 66 deg F right now. The temps are supposed to be lower tomorrow.

i want out of this state, lol
or to at least get the ac fix in the fiero now
going to do that tonight

it was 97 degrees today
right now its 94 with a heat index of 99
it was an actual 100 degrees at 4pm saturday
spring is wound a little tight around here this year lol

quote Originally posted by yashmack: any update on this? im having very similair problems with my fiero i still havent got a pressure gauge >.> I will be getting one this week was the problem with the fuel pump or with the regulator? the reason i ask is that i suspect something wrong with my regulator there have been several times that the car will stall out and when i press the shrader valve air comes out i cant see how the puel pump would be pumping or allowing air in and the only thing that makes sense to me is the regulator could be out the car did sit for a while before i got it and has been sitting off and on since i got it im going to hopefully get it inspected tomorrow and hopefully start diagnosing the issue again my truck died on me this weekend so i am having to repair the fiero sooner than i was planning hoped to sell the truck and fix the car, now it looks like ive gotta fix the car, then the truck and decide what to do later, lol updates!! need em

Ooops!

I usually provide a final update once the problem is solved. Apparently I did not do this here...

It turned out that the pump was fouled by fine rust particles that both got through and also clogged the fuel strainer. Replacing the pump and cleaning the tank thoroughly solved my issues.

When I dropped the fuel tank it was obvious I did not do a very good job of cleaning the tank from the previous fuel pump replacement. After looking at some used tanks and not finding any that were not corroded I decided to try cleaning this one out better. I used about 1400 BB's inside the tank and shook it as violently as I could for about a total of 15 minutes. It took a couple of hours because I had to rest between shaking it for a minute or two. Then getting all the BB's out and rinsing out all the fine rust powder takes a while too. However, the result was much, much better than before. I suspect the new pump and strainer will last more than a couple of years before giving the same trouble. The car has been running fine since I installed the new fuel pump.

Charlie

quote Originally posted by yashmack: it was 97 degrees today right now its 94 with a heat index of 99 it was an actual 100 degrees at 4pm saturday spring is wound a little tight around here this year lol

I worked for the Union Pacific Railroad from 95-96 in Ft Worth so I feel your pain.

Let us know how the fuel pressure looks. And the pressure should hold after the key is OFF for several minutes.

ok so the 15 dollar gauge from harbor freight sucks, it has a leak around the connection hose at the fitting for the gauge itself >.>

it goes up to about 20 psi when i first turn the key and slowly drops after the pump stops
this could be due to the leaky pressure gauge or something else, i really have no idea now
there is no o-ring between the adapter hose and the gauge....
i dunno if there is supposed to one there or not but it does leak around the fitting for the gauge
im going to go get my money back tomorrow or see if there is a part missing, like an o-ring

i cant find what its supposed to read in the service manual either
its says to refer to section 6EF and then that section doesnt exist...

ok, i moved an o ring from one of the other hoses that came in the kit and got it to seal
it holds pressure at 22 but no higher
i crimped off the return line and still only up to 22 psi
looks like i got a bad pump most likely
ive already replaced the filter so that is most likely not the cause
going to give it to the mechanic tomorrow and tell him what ive done
hope to have her back in a few days

by the way i apologize for hijacking your thread hehehe

[This message has been edited by yashmack (edited 06-08-2010).]

Damn it's nice to have test tools, and to see what's happening!

Nice to see someone actually troubleshoot instead of just pre-conceiving some part bad and then trying to prove that part is bad without testing anything. Cheaper on the wallet, but it doesn't make the parts store quite as happy.