This is in regards to my '89 IROC (L98, TPI).

It seems my car has developed a new problem out of nowhere. I noticed the past few mornings, when I get up and drive off for school, I can have the pedal down about half throttle but my car will just chug along slowly picking up speed. Then, out of nowhere, it will just "kick in" and start driving normally. This is pretty much on the first one or two takeoffs. At first I thought it was something slipping in the drivetrain but then I realized that the engine speed wasn't picking up.

However, I learned today that this isn't something that just happens when the engine is cold. I was leaving a Starbucks after having been there for only about an hour, started the engine, and then it idled down after a few seconds and died. Started again and same thing. Then, I gave it some gas the next time it started up and kept the engine speed at about 2500 RPM. When I let off, it barely wanted to idle, but it didn't die. So then I put it into reverse and gave it some gas to pull out of my parking space, and it just died in the middle of the street while I was pulling out. I tried starting it several times, but it wouldn't even start. After about three minutes, it finally started and it acted fine after I got it on the road.

Any idea what the problem could be? I tried tapping the MAF sensor but that didn't help--and I'm not too surprised since the computer wasn't throwing any codes. Also, I changed the fuel pump less than six months ago.

Thanks in advance!

 

Can you hear the fuel pump whine? I would check the pressure at the feed line.

 

Hi. I have a similar problem. Would anyone know the cause of this issue? My GTA has been randomly stuttering when I press the gas and hesitating. There are no check engine codes. This problem happens for a few minutes and then just suddenly goes away. It started out happening like once a week for a few weeks and now it happens like every day. I think it back fired a few times. What could it be? Maybe a bad MAF? Thanks.
-Crystal

 

Is your fuel filter clogged? That applies to Sancho and cryztal.

 

Hi thanks for the suggestion about the fuel filter. I was thinking maybe it was that and was going to have it changed. But could that cause intermittent problems? Because the problem I have only occurs like 5-10% of the time I am driving. It is so bizarre how it happens then just goes away. It doesnt seem to matter if the car is warm, but it happens shortly after start up, seems after I drive a mile or so. Then I hit the gas and barely any response and the rpm is struggling to rise, rising a pinch and dropping (hesitation). It's wierd. I wish I knew the cause. Thanks for any suggestions.
Crystal

 

When was the last time you opened it up and blew the carbon out of the system, maybe added some injector cleaner to the fuel. Just a thought!!!!!!!!!!

 

Also, whens the last time you did a simple tune up? Cap, rotor, wires, plugs, all that good stuff.

 

Hi. Thanks for the replies. The last time it was acting up, yesterday, I unplugged the MAF sensor. Then it acted worse making popping noises. A month ago or so the MAF sensor connector came undone and got chewed up by the fan. I put on a new connector a few weeks ago. After that the check engine light came on with Code 36, MAF burnoff circuit. That code is cleared now and hasn't come back. Two weeks ago the car got new plugs & wires. Not that long ago it got a new msd distributor, distributor cap and ignition module. Pretty much 80% of the car has been replaced, =). That's my estimate. I put all my money into the car. So I hope to figure this problem out. The last time I opened the butterfly and cleaned it out must have been a year ago or something like that, I am not sure. Thanks and any more suggestion might help.
Crystal

 

I would still double check your fuel pump and make sure you pump is keeping up. You have the typical symptoms of a fuel pump that is on its way out.

 

Hi. Thanks for the help. My brother mentioned the fuel pump. But I thought it would act up all the time and not just some of the time. Could a fuel pump on its way out give low fuel pressure some times and other times be fine? How do I test the fuel pump? Do I check the fuel pressure when I am having this problem and check it when I am not having a problem and compare? What kind of fuel pressure should I be getting? Thanks.
-Crystal

 

I would check with the guys on the TPI board. They know their stuff and can recomend the best method for testing feed line pressure. I belive you will need 40 to 50 PSI at the regulator. A failing pump can work like you described and be fine one minute and then suck the next.

 

There is a Schrader valve on the fuel rail. Attach a fuel pressure gauge to it & disconnect the vacuum line to the fuel pressure regulator. The pressure should be a steady 38-45 psi.

 

Can you explain why you disconnect the vacuum line to check? I was reading my pontiac manual for 88 350's it was saying the regulator is built to provide a steady 36 PSI through the fuel rails (which is where your gauge attaches), But I have heard about this pulling the vacuum on these boards before, but could not find anything in the manuals about that. What affect does pulling the vacuum line have, increase pressure decrease pressure??

 

"Don't tell me I have to change my fuel pump again... :"

Your low on headlight coolant.

 

I was kind of curious about that also. Why pull the vacuum line to test fuel pressure if the engine is off and there is no vacuum to begin with. I thought it was that you pulled the vacuum line when you had the engine running and wanted to adjust or set the adjustable fuel pressure regulator. My, my, my.

 

Doing some more research I think I have my own answer so I will post it for anyone else. Trickster I think it was mistated to check pressure with vacuum off during just the "key on, motor off" check. This check is where I am still slightly confused. I believe this checks for leakdown to see if your pressure stays stable after priming. Now with the Holley AFPR (I just bought one not on yet) I was reading another post where it was stated they are designed to release pressure during this test SO not sure whats up with that.

In general the difference in vacuum on or off during check is.

Vacuum hose off = Simulates WOT setting do to vacuum at 0, so this is the condition you want to set your max pressure.

Vacuum hose on = This will drop somwhere between 5-10 PSI lower than your vacuum hose off setting. So as the Pontiac manual states our stock regulators (in the 88 350's at least and probably most) should be pushing about 36 PSI. So if you install your gauge up to your rail and have the vacuum connected, as in normal driving operation, you should see somewhere in the 36psi range on your gauge when you pop the hood.

 

Hello omcrider,

I have a friend who just bought and installed a holley AFPR. On this particular AFPR, after the system primes and you get a fast reading, it does bleed off rather fast. Irritated him no end when he found out about that function. He thought he had a bad AFPR and bad injectors and a few other things. I have done the fuel pressure check numerous times with the engine off and have not disconnected the vacuum line. That particular step is not even mentioned in the GM service manual for checking fuel pressure.

 

Right you are Trickster, I was a little dissapointed that my expensive very thick original GM service manual had very little on actually checking fuel pressure under different conditions. It did have some good diagnosing trees to help determine problems but they also sometimes left something to be desired. I guess they were written for profesional GM mechanics and not your backyard technician, so some of the basic stuff like "apply 12v to fuel pump relay to check blah blah," yet it doesn't give you the steps required to do that, so if you don't already know how, your still stuck. So a combination of the book and these boards really helps things come together.

 

I agree, but look at when those books were written and what we have learned since. What did your manual run you, mine was $60.00 and has gone up to $146.00 since I bought mine. But geez, they sure beat haynes or chilton.

 

They sure are I got mine off ebay for about $45 bucks, It is way more complete than either Chiltons or Haynes.