I recently bought this car and I have a drivability issue I need help with. The car is a 305 5 speed, headers, cats removed, and egr vacuum lines plugged. The fuel pump will go to approximately 40+- psi when I turn the key on, but immediately drops when the relay cut the pump power. The car starts fine and will idle as long as you want. The pump holds about 40+- psi when the car is running and gains a couple pounds when you hard rev the engine, pressure never drops while sitting still. The seller said it has a new TPS (I checked the ohms to verify), IAC, plugs and wires. I have installed a new pressure regulator, cleaned the injectors, air temp sensor under the plenum. The car will crank and idle with no problems, it will rev sitting still with no problems even when warm, It seems to drive normal driving no problems, the issue comes in once there is some heat (around 180 or so and up probably) and at medium to hard acceleration it wants to spit and buck. When I go back to normal driving it runs OK. I assume it must be the fuel pump since it is about the only thing not replaced? Sorry for the long description, but I wanted to put as much info as possible.

 

Take close up , detailed, in focus pictures of your injectors and any part numbers on them and by where the injector connector is looking for a stylized "RP" logo and post them in your thread. You should be able to rotate the injector some if need be to get the pictures.

If your car has its original GM Rochester Products fuel injectors then they are junk and should be thrown away and replaced with the proper Delphi fuel injectors for your application.

 

What pressure regulator did you install?

 

It is an AC Delco regulator

 

What is the fuel pressure when....

 

I did not have a gauge on it then. I do not have a permanate gauge in the car.

 

My initial hunch is you are correct, I had similar behavior with my first GTA when the fuel pump was going bad - that being said it wont hurt to verify some other things before dropping tank. How are the condition of your ignition components? cap/rotor/ignition module (get it tested)/pickup coil - these could be corroded and causing issues under heat/load.

 

Need to see the pressure when the symptom is happening. When the symptom is happening.

Doesn't need to be a permanent gauge. Duct Tape it (or affix it how ever you prefer) to your windshield or bring it into the car so that you can see it while driving....while the symptom is occurring.

 

Did this problem just occur or has it been this way since you purchased it?

 

I will put the fuel pressure gauge on it and run it down the road.

 

Yes, it has happened since I bought the car, maybe around a month or so. I changed the typical parts hoping it was one of these, other than the fuel pump. It has not had the check engine light on at any time.

 

I put the fuel pressure gauge on the car yesterday and ran it down the road. The pressure did drop to 25-30 psi when I ran the car up to around 3/4 throttle, but the car did not jump and buck. At normal driving the psi stayed around the 38 -40 psi range. I think some of the difference is the car did not have alot of heat in the engine yesterday when I drove it. It was threatening rain so it was a quick run down the road and back and it never acted up. Maybe the pump is getting hot the longer I drive. Needless to say with the pump dropping pressure, I will be replacing it soon

 

IMHO I think you need a tune. My best freind has a 92 G92 car, 5 speed. He experiences the EXACT same issue with the bucking @ high rpm/acceleration. His started after an injector change. Usually when mods are made to the car the tune needs to be adjusted. This is the case with your car, headers, not cat, no EGR. This could be enough to throw your fueling off and causing a lean/rich condition in the higher RPM's when the engine is hot which is what causes bucking/hesitation. The computer sees the EGR system so with it just removed you are throwing something off just in that system. With headers, if the O2 sensor wasn't changed to a heated one it will read wrong as it does not come up to temp like in the stock manni's. Are your injectors original?
Before the tune this happened every time he drove the car, now after a round of dialing the tune in it very rarely happens any more. It also helped his overall performance and the car runs better now than it has in a minute!

 

I think he needs a pump. I think that seems pretty obvious at this point. The tune isn't the cause this driveability issue.

Also, he doesn't NEED a tune b/c of exhaust and EGR. Car will run fine...even great, on the stock tune with exhaust and no EGR. Many an F-body owner has ran their F-bods with exhausts, EGR's missing...and a lot more, and had satisfactory results (no driveability issues). Myself included.

A tune would help (if it's any good)...but it isn't a NEED. If course, a tune would help, even on a box-stock car, right? Right. Every car "needs" a tune, but it's NOT HELPFUL when people recommend tunes to "fix" driveability issues that are caused by actual problems. That is called, "Giving bad advice". Fix the problem...then consider a tune for the reasons that you would tune any car.

 

Your opinion Tom, all I have to say is it what's fixed my buddies "drive ability" issue which is the same exact issue the OP has.

 

My opinion? That's years of experience, driving the OP toward an actual diagnosis.

Did it though?
Doesn't sound FIXED, to me. So "get a tune" advice was really, a WAG.

Giving advice to people needing help that is based on "a buddies problem" that was sort of, maybe? fixed, isn't really good advice. I'm sorry to be an a-hole, but it isn't. Giving diagnostic advice to HELP (teach him to fish) the OP identify the problem, that is giving good help. As a mechanic, and the boss of mechanics for 30+ years, that's how we do it. We diagnose first. The OP identified 25 PSI fuel pressure under load. That is an objective problem. That needs to be fixed....then you posted that he should get a tune?

Did you read the thread I linked? "It needs a tune! It needs a tune!". Was that good advice? No, it wasn't.

 

You are right...I am out!

 

if its not fueling its probably an ignition problem. The ICM will do the exact thing when they get faulty especially when they heat up.

 

I put a new fuel pump in over the weekend, took it out for a test drive and got about 1 1/2 miles and the pump stopped. It seemed to have fixed the stumble I had been having before shutting off. I drug it home and could not hear the pump kick on, so I got busy for a few minutes, then went back and laid under the car with a stick and moved the bulk head connector around. I hooked up my pressure gauge to make sure it wasn't pumping and when I turned the key the pump kicked on. I turned the key again to prime the system and then I started the car. I let it idle watching the pressure and it acted like there was no problem. I turned it off and restarted it multiple times (no driving time) revved it several times and no problem. I hope it was a loose connection, but I need to make sure my neighbor is home before taking it down the road again. I did notice my electric fan did not turn on once it got up to temp, so I will be replacing the fan sensor.

Has anyone removed the in tank pump and run an external pump on one of these cars. If so what tank pickup was used. It would make like much easier when the pump dies.

 

how's your fuel pump relay? That could be the problem. In-tank pumps should generally be pretty reliable.

 

You have three things to check, at this point: the fuel pump relay that ULTM8Z brought up, the fuel pump fuse, and the oil pressure switch. The pump should have kept running on the oil pressure switch, even if the relay were bad. But it didn't, so that already went bad previously...or the fuse blew, which would cut power to both the oil switch and the relay.

 

I have not checked the relay with a multi meter yet. I did hear the relay clicking on and off and could feel it also. Initially the pump still didn't kick on, but did later, which is why I think it was either the bulk head plug was maybe loose or the pump stopped for some reason. It has been raining every afternoon when I get home, so I have not had the opportunity to check and see if the car will crank.

 

I know it's not the fuse, because it started working again and I had not changed the fuse. I don't think it is the relay because I was driving the car when the pump stopped working. I could hear the relay clicking when I was on the side of the road, and once I got it home. I have not checked it with a multi meter yet. Maybe the oil pressure switch, but the car had oil pressure just before it shut off, I am very much a gauge watcher in my older cars.

 

The relay should also be providing power at the same time, in parallel with the relay. The importance of the oil pressure switch in this case is one of two things:
1. If the oil pressure switch is functioning properly, the problem that caused the pump to stop is somewhere in the circuit that is common to BOTH the oil pressure switch AND the Relay. You can test the oil pressure switch, and if it's good, then for sure it wasn't the relay, either. It was something else.
2. Is the oil pressure switch bad? If it is, and then the relay could have caused the problem. Could have. Not likely, but possible.

Anyway...that's an interesting correlation between wiggling your bulkhead connector and the pump working again. I'm can't recall if the FP circuit runs through the bulkhead or not but if it does, I'd scrutinize that.

 

So I finally had a chance to run the car down the road this weekend. I drove it normal and ran it up hard threw the gears into 4th a couple times. It did not stumble or shut off, so I have to assume the bulk head connector was loose, even though I still don't think that was the problem. Next chance I get I will take it for a longer cruise and see what happens, of course with a friend on speed dial just incase.

I do have another issue though, my radiator fans never kicked on when I let it get just above 220. I have changed the sensor on the pass side. The fan does come on with a clip in the OBD plug. What else could be the issue.

 

Fan relay(s) may be bad. Or the wiring going to the relay.

If you turn on the ignition, then take the wire off the sensor and ground it, do you hear the relay trigger? That would at least diagnose the secondary fan relay.

If you can ground the trigger side of the primary fan relay (the wire that goes to the ECM) then you can prove out the primary relay too.

 

I finally found what was causing my fuel pump issues. Before Hurricane Helene skirted the coast of Florida, I had moved the car. It started, but was a hard start. Once we were in the clear I was going to move the car again and it wouldn't crank, because the fuel pump was not running. Well here comes Hurricane Milton so I didn't get to work on it any for a little bit. I checked the wiring at the bulk head going from inside the car to outside the car and it was working correctly with the relays cutting power after a couple seconds. So I went ahead and bought another new pump, dropped the tank, installed the new pump and put the tank back in. I did not finish the job before checking it and it still did not work, so I pulled the tank back out and did an ohms test on the sending unit wiring. Come to find out the in tank plug had gotten hot at some point, slightly melted the plug and lost connection. I fixed that problem, plugged the sending unit with the pump attached and hit the key and it worked. After a few mile drive running the car up to speed, it seems everything is good now. What a PITA. The only good thing is now I have a spare pump in stock. Thanks for everyone's help.

 

Thanks for updating the thread with your solution.

Glad it didnt need a "tune".

 

"Need". Some folks don't know the definition of the word...especially when it comes to tunes.

Glad the problem was diag'd and repaired.

 

I don't appreciate the dig dude. Here is your quote, " I think he needs a pump. I think that seems pretty obvious at this point." ... I guess you need to look up the definition of the word.

 

Glad you found the melted plug, that's a tricky one! As I've learned the hard way, sometimes the only way to troubleshoot is to dig in and inspect every little thing. Don't know why people get so hostile on this board sometimes - we are all working toward the same goal, if you think someone is wrong about something just state your opinion and move on, there's no need to keep chiding them.

 

It wasn't directed at you. I was actually replying to Aaron R. and in my head, it was about a different thread and a different person's comments, I think Aaron is aware of...and in that context, it was meant to be humorous. Anyway, it probably looked like it was directed at you Vinny, so I apologize if it did.

You're point is valid, however....I did say that and it apparently wasn't the pump, but rather the wiring.

 

Thank you Tom.

 

vinny, Tom and I are often on the same page about some other weird things on these forums. Wasn't a dig at you but I can definitely see why it looked that way. Sorry about that.

Thanks for being a good sport too and shaking hands after the dust cleared. Too many people walk away from a discussion when they cant handle a disagreement. Good to see a lively discussion, solution, then everybody having a good laugh and a beer afterwards.