Help! 86 dies with full tank

[Dcalebaugh]

Here is my challenge. When my tank is full the car is undriveable. It acts as if it is starving for fuel. If I drain the tank down to about half it runs perfect. This has been going on since I took it out for the summer last year. I have replaced so far: fuel pump, pulsator, sock, inline filter and relay. I even tried to simulate the problem by placing 120 pounds of weight in the back of the car while having a half tank to simulate the extra weight of ten gallons of gas thinking that maybe something is getting pinched by the weight of a full tank. No go. I have tried the full tank several times and each time it was undriveable, it wont idle and to keep it running at all I have to pump the pedal continuosly. I drain it to a half and it's fine. The tank looked ok inside from what I could see when I replaced the pump. I am questioning a venting problem but do not know how or if thats possible.

Thanks in advance,

Dave

 

[bradslt5]

i dont know if this will help, just an idea i had .have you looked a the vapor recovery system. is the charcoal canister and the parts that make it work. does the gas cap make that pffff sound when you open it . ck the return line and see if everything is ok there . do you have a factory service manual?if not i would get one .itwould greatly help diagnosing your problem. hope this helps o

 

[Dcalebaugh]

I am looking at the charcoal canister purge system as I don't know where else to look. I have the GM shop manual and it describes a problem with the purge system as a rich fuel problem, not what I appear to have. I thought for sure that of all the C4 owners I would not be the only one that ever had this problem. There is a direct corrulation between a full tank and a half empty tank.

 

[Ezmunie]

I wish I could help you with your problem, but I have never heard of having that kind of situation. It also sounds like a venting thing to me, but I wouldn't know for sure. Please let us know when you find out what it is.

 

[bradslt5]

ck to see if there is a ck valve somewhere in your system. our zr1s are alot different . but trying to be logical about it ,gives thought to a ck valve being bad somewhere . good luck.

 

[kenmack]

How about

Whenit's running like crap,try and do a fuel pressure test,Hell Idon't know,but these cars are extremely sensitive to the correct fuel pressure,maybe your new pump is a bum one .Weird!!!!!!!

 

[Bobsvette]

Here's my question, have you tried running the car with the gas cap off with a full tank? Also I don't know where it woud be located but there has to be a emergency cut off switch somewhere (you see them near one of the hinges is trunks of regular cars) and maybe when the tank's full it's reacting to it?

 

[Dcalebaugh]

The only thing I see that I havent checked on the tank is a vapor connector that is located just to the left of the sending unit. It appears to be bolted in place with two hose connections. One is the vapor line from the tank and the other is the vapor line that goes to the purge cannister. This all started last year when I took the car out for the summer. I always store the car with a full tank and add stabilizer.

 

[Dcalebaugh]

I have not done a pressure check yet, might be a good idea to get a gauge. However as soon as I drain off a half tank it runs great?

 

[Dcalebaugh]

Checked the charcoal cannister and purge solenoid. All functions properly. Next!!!

 

[Dcalebaugh]

Ok. Bought a pressure gauge and checked the pressure. With the key on but no start pressure jumps to 42 then down to around 18-19, engine running pressure fluctuates 35 to 36 psi.

 

[Dcalebaugh]

Ok update. Today I drove to work. Approx 1/4 tank of gas. Ran fine for ten minutes then fell on it's face big time. The only way I was able to get it to work was by continually pumping the gas pedal as fast as I could. Got to work shut off the car then tuned it back on and it started right up like nothing had ever happened. Started it up for the trip home and ran fine for about 2 miles then same thing. Limped it home by stopping several times and shutting it off then restart and it would run for a short amount of time just fine then start acting up again. Got it home and put the fuel pressure gauge on it and it was running at idle between 35 and 36. It took a while to get it to act up in the garage but when it did the fuel pressure bounced all over with a high of maybe in the 20's and a low near nothing. Turned it off and then back on and the pressure was fine and the car idled perfect. Would a pressure regulator act this way?

Thanks,

Dave

 

[bradslt5]

if it were me , i would replace the pressure regulator first . then clean the entire fuel system . every line to and from the tank .also clean the tank.to often we forget that our cars are aproaching 20years old . and deposits form and then get dislodged causing all sorts of problems . you could do the whole thing in a day. it really sounds like you got something floating in your fuel system . hope this helps and good luck

 

[Dcalebaugh]

Latest. I read that if you pull the vacum line off of the regulator that it will increase the pressure up towards 60 psi. When I pulled the vacum line off I replicated what has been going on, that is the pressure gauge fluctuated radically and the car stalled out as if it was starved for fuel. I have ordered a regulator rebuild kit and am hopefull. Any tips on pulling the intake to get at the regulator?

Thanks,
Dave

 

[vetteboy86]

You need to take the plenum off to do it right, heck to do it at all actually. It isn't that difficult. Take the bolts from the top of the tube runners off, either take the Throttle body off, or unhook everything from it. Don't forget the hard line in the rear for the vacuum booster.

Once everything is loose, slowly pull the plenum out. I I have never heard that the fuel pressure should jump to 60 when the vacuum line is unplugged. Usually when the fuel pressure is set on a vehicle, it is set with the vacuum line unplugged. This way, as the engine increases in rpm's the maximum amount of fuel pressure is what just got set. Most cases this is in the mid 40's.

Oh, I think I had the similar issue when I had a full tank. I think mine was a venting issue. Now I just dont top off the tank when I fill it.

 

[Dcalebaugh]

Thanks for the reply. Here is it what I have recently done. The shop manual says to add 10 inches of vacuum to the regulator and the pressure should drop 3-10 psi. Mine actually rises for a time and then eventually fluctuates wildly and the car stalls. I tried pinching the return line and the feed line with similar results. When it dies the pressure gauge fluctuates radically and after it stalls there is a weird clicking or pulsating sound that I can hear under the plenum until the fuel pump stops.

Dave

 

[vetteboy86]

When mine went bad, I actually removed the vacuum line to the regulator, and fuel was pouring out. I also, went through one gauge before I found one to work. The original I bought gave me erratic readings. The next one, reads solid as ever.

 

[Dcalebaugh]

Well today for what it was worth I changed the fuel filter again. I had a new one installed when I put in the new pump last week. But I thought maybe something got stirred up when the pump was changed so for the $9 might just as well. Unfortunately that would have been to simple. It starts and idles fine but the minute I give it any throttle it starves and dies. I did get a rebuild kit for the regulator but the more I read about the regulator the less I think this is the problem. I have not read about anyone having a regulator go bad and make the car undriveable, run crappy but not die.

Dave

 

[G Winter]

Have you checked the TPS ? If I am not mistaken the ECM uses those readings in part to control injector pulse. Someone correct if I am wrong.

Glenn

 

[Dcalebaugh]

No not yet. What really throws me off is the second I pull the vacuum line off of the pressure regulator it starts surging really bad and the fuel pressure gauge goes crazy and the car stalls. Even if I manage to get the vacuum line back on before it stalls it still surges and stalls. All I do then is turn off the key and turn it back on and it starts right up and idles fine until I either pull the vacuum line or try to rev the engine up then it repeats the process. I have most of the air intake stuff loose and ready to pull off so I can rebuild the regulator and eliminate that as a problem. I am also going to do a flow test to verify if I am running out of fuel.

Dave