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 Page 1 of 2 12
Username Post: 91 350 tbi issues        (Topic#249910)
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-27-10 09:41 AM - Post#1981498    

ok I have seen lots of topics on this issue and I have tried every solution i could find but nothing has worked so i turn to you all. I have a 91 chevy 1500 350 tbi. When it is started cold, the idle surges from between 500-1500 until it is warmed up or you are driving down the road. It will often stall when first started because of this. The surging continues no matter how much you have you foot in the gas unless u floor it, but when you let off it starts surging again, or until you are going about 10-15 mph then it stops surging, making for very jerky takeoffs the first few start/stops. It also stumbles badly until it is warmed up then it seems to be ok. It will also stall some times no matter what temp it is but does it worse in cooler temps, (early morning, late night), when you are just about to come to a stop or when you are trying to back in a parking spot where you are just letting the truck move on it own with no throttle input. This is what I have done to try and fix this issue with no luck. I have removed the TBI unit and cleaned it out thoroughly then reinstalled with a new gasket. (I did not remove the fuel pressure regulator/ injector assy from TB because i did not have gaskets to reassemble, thats my next move.) I have replaced the IAC, TPS, EGR valve, coolant temp sensor (right next to water neck), o2 sensor, fuel filter, MAP sensor, spark plugs & PCV valve. All vacuum lines are connected correctly and none are blocked. The timing is set to 0 deg. BTC per underhood label. Both injectors appear to have a good cone spray pattern. I checked the computer for fault codes and it gave me a code that the ignition control module is malfunctioning. I have no relaced that yet. Then on the drive to work this morning the SES light came on. I have not pulled the code for that yet. Im still at work. It was a bit cooler this morning than it has been for a while, that might have something to do with it. Please help. This is my daily driver and I really like my truck. Thanks.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
Low priced Genuine GM Auto Parts
someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
09-27-10 09:48 AM - Post#1981502    
    In response to tardisguy

Could you give us the actual code # you read? If it was 12, that is normal. If it was 42, check that your EST bypass wire is connected - the tan/black wire you disconnect to set base timing. If it was 43, on these trucks that is a knock sensor error.

What brand EGR did you buy and how was it selected?

Have you actually checked all around for vacuum leaks?

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-27-10 10:39 AM - Post#1981520    
    In response to someotherguy

yeah get the actual code, that will help. Also 90% of the time these TBIs surge it is going to be some kind of vacuum leak. The worse the surging the bigger the vacuum leak.
98 Silverado k1500 4x4 350


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-27-10 02:41 PM - Post#1981591    
    In response to 355Cheyenne

ok I just went outside and pulled the codes from the computer and the only code it has is #44 oxygen sensor circuit lean. I just replaced the oxygen sensor so what else could it be. The other code that it had is no longer there so I guess there is nothing wrong with the ignition module.

The EGR brand is BWD. They had it in stock instead of waiting for the AC Delco plus it was 30 bucks cheaper.

All the vacuum lines are in good shape. None are cracked and the rubber ends are still flexable. I replaced the gasket below the TB and made sure the sealing surfaces on both the TB and intake were clean. Another thing I noticed that I did not put in the original post is that the oil pressure gauge in the dash moves alot. The higher the engine RPM the higher to oil pressure goes. Is that normal on these trucks or not. I have a 86 monte carlo SS with a 305 and I have not noticed the oil pressure gauge moving that much in the car. I have only had the the truck a month and it started doing this after I ran a bottle of Gumout fuel injector cleaner through it. Thanks
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-27-10 05:03 PM - Post#1981651    
    In response to tardisguy

Oil pressure should increase as the RPM increases, that is fine. I know you said you checked for vacuum leaks, but all I can say is you need to look harder. a lean code + surging = vacuum leak. 100% sure now you have a leak some where. Now That being said after checking the easy stuff the other thing to check would be intake gasket. Pull all hoses off the valve covers and plug them, do you feel vacuum off the valve covers? if yes then you have a vacuum leak via bad intake gaskets.


I am 100% sure it is a vacuum leak.
Tom
98 Silverado k1500 4x4 350


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-28-10 08:18 AM - Post#1981900    
    In response to 355Cheyenne

OK I just went outside and started the truck, pulled the air cleaner, pulled the pcv valve out of the valve cover with the vacuum hose still attached. I also pulled the pipe that leads from the drivers side valve cover to the spacer that sits between the TB and the air cleaner. I plugged both of those and there was no vacuum coming from the hole in the valve cover where the PCV valve goes. Can there be a vacuum leak inside the TB somewhere because when it is surging, it makes a loud sucking sound, but when it is warmed up it makes the normal light sucking sound.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-28-10 10:05 AM - Post#1981926    
    In response to tardisguy

It is possible that the TB is wore out and it is leaking past the throttle plates or through the throttle plate shafts but given the evidence I think the leak is a lot larger.

You seem to have ruled out a leaky intake gasket. The next step is to isolate all vacuum accessories. First check the base of the TB where all the vacuum lines attach. There will be some up front and in back. Make sure there are no open ports. If there is, feel for vacuum. If you find an open port then that is the problem and plug it. If you do not find a open port then start pulling them 1 at a time and plug the port on the TB with your finger. If you find one that when plugged with your finger causes the problem to stop then that vacuum circuit has a fault and needs to be investigated and traced.

Tom
98 Silverado k1500 4x4 350


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-28-10 12:18 PM - Post#1981974    
    In response to 355Cheyenne

ok will try that. There is also a tube that comes off the intake drivers side under and slightly forward of the TB that leads to the brake booster. Could that also cause a vacuum leak?
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-28-10 01:31 PM - Post#1982009    
    In response to tardisguy

yes, both the fitting on the intake, hose and brake booster. You can spray carb cleaner on the fitting and hose and if it causes a change in idle, that would indicate you found a leak.
98 Silverado k1500 4x4 350


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3014

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
09-28-10 01:33 PM - Post#1982010    
    In response to tardisguy

It set a lean code, and it surges.

Test the fuel pressure with the engine running.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-28-10 01:47 PM - Post#1982014    
    In response to Chevytech

  • Chevytech Said:
It set a lean code, and it surges.

Test the fuel pressure with the engine running.





Very good point actually, it could be low fuel pressure as well.
98 Silverado k1500 4x4 350


 
someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
09-28-10 03:36 PM - Post#1982066    
    In response to tardisguy

  • tardisguy Said:
Can there be a vacuum leak inside the TB somewhere because when it is surging, it makes a loud sucking sound, but when it is warmed up it makes the normal light sucking sound.



When the idle speed drops, the ECM commands the IAC to open in an attempt to raise the idle back to normal. If the idle is dropping very low, the IAC is wide open. This is the cause of the sucking sound you're hearing. It's not the cause of your problem, just a symptom.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
Bill K.b 
Senior Member
Posts: 4259

Loc: upstate NY
Reg: 10-24-05
09-28-10 08:08 PM - Post#1982196    
    In response to someotherguy

Since the hose off the PCV goes to the throttle body, it should pull vaccuum through the PCV and the hose, not from the valve cover opening into the engine.
Those who can, do. Those who can't, criticize it on the internet.

1988 G20 van 5.7L - driver.
1993 3500 dually 5.7L NV4500 - tow truck
1991 G20 van - parts truck

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-29-10 05:43 AM - Post#1982317    
    In response to Bill K.b

Yeah it was sucking like mad through the PCV valve but there was no sucking from the valve cover so that’s good.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-29-10 06:19 AM - Post#1982326    
    In response to tardisguy

Well it shouldn't be sucking like mad from the PCV all the time. If you put your finger over the pcv blocking it off, does it idle better? You may need a new PCV is all.
98 Silverado k1500 4x4 350


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-29-10 07:11 AM - Post#1982347    
    In response to 355Cheyenne

I can hear the PCV valve clicking about 6 times a second and it has strong vacuum. Finger over end of PCV valve that sticks in the valve cover stops click but does not change idle issue.

Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
09-29-10 07:18 AM - Post#1982348    
    In response to tardisguy

hmmm
98 Silverado k1500 4x4 350


 
someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
09-29-10 07:57 AM - Post#1982365    
    In response to 355Cheyenne

The way I've always understood to check for vacuum leak due to bad intake gaskets (thanks to CDAUSA) is to remove the PCV and breather hoses from the valve covers, plug the holes in both valve covers, then remove the dipstick and see if the dipstick tube has vacuum. Some like to put a vacuum gauge on it, but you'd probably be able to feel it by plugging with your finger. If in doubt, use the gauge.

If so, bad intake gaskets causing vacuum leak.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-29-10 07:59 AM - Post#1982366    
    In response to 355Cheyenne

Does Autozone or Advance have a fuel pressure gauge in their loan a tool program or do I just need to buy one.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
09-29-10 08:12 AM - Post#1982370    
    In response to tardisguy

As much as I hate to recommend Harbor Freight, they have a simple fuel pressure test kit #92699 that is $20. Combine that with a coupon from numerous magazines and it'll be really cheap. Do note the "Made in USA" sticker on the first picture is not the set from Harbor Freight, but their kit is essentially the same parts. This same style kit is usually at most auto parts stores for a little more money.

The only catch is that the particular style isn't suited for testing TBI engines, as TBI's don't have a test port. HOWEVER...easy to remedy.

Inexpensive way: attach two scrap pieces of 3/8" fuel injection hose on either end of the Tee, then carefully force it over the ends of the hard line where the filter goes. It shoves on so firmly that you rarely need clamps at those ends (but do clamp it at the Tee.):


Lay out a few more bucks: get the Actron 0180-000-1320 test Tee fitting and use the cheapie Harbor Freight gauge set on it. You can mount it either between the hardline and fuel filter, or at the rear of the TBI unit. You can leave this there permanently if you like. It costs about $10 from online sources or even cheaper directly from Actron. Don't be suckered into spending $20 or more like I did before I found out Actron has it cheaper.


A little bit more money: get the whole kit from Actron - model # CP7817 test kit which includes the pressure gauge, hoses, and T fitting all in one package. About $40-$50 from most online sources, probably available at some auto parts stores for a little more. It's also got a nice pressure relief valve and hose.


If you find yourself working on EFI engines, a fuel pressure test kit is a necessary tool for your box.

Of course, both options - the cheapie HF gauge, and the Actron gauge, will also work for testing Vortec and many other engines that have the standard schrader valve test port built-in.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-30-10 12:03 PM - Post#1982961    
    In response to someotherguy

ok the low fuel pressure sounds a more likely suspect now. I did what 355 Cheyenne said about pulling one vacuum hose at a time and plugging the hole to see if that made the idle better and none really did anything to change the idle surge. I am still trying to see if I can borrow a fuel pressure tester so I don't have to buy one right now. The hunt goes on......
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
09-30-10 12:05 PM - Post#1982962    
    In response to tardisguy

The haynes manual says that the oil pressure switch is also the fuel pressure switch. If that is bad could that be causing the surge because it is telling the comupter the wrong thing.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
09-30-10 12:28 PM - Post#1982969    
    In response to tardisguy

No...the way the oil pressure switch figures into the mix can be misleading. The oil pressure switch is only there to engage the fuel pump in the event that the fuel pump relay fails. A symptom of this can be long crank times before the engine fires up; this is because as the oil pressure sensor sees about 4psi from you cranking the engine over, it completes the circuit and fires the pump.

* Not sure if this is 100% correct so adding this disclaimer until I can get the straight story.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


Edited by someotherguy on 11-29-10 10:52 AM. Reason for edit: No reason given.

 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
10-05-10 09:14 AM - Post#1985041    
    In response to someotherguy

I have not tested the fuel pressure yet. im gonna buy a tester this weekend. If the fuel pump is bad, do you recomend replacing just the pump or the whole unit (pump, sending unit, etc.)
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
10-11-10 07:13 AM - Post#1987759    
    In response to tardisguy

The truck has also become difficult to start once it is warmed up. If you drive for a while then stop and like run into the auto parts store real quick like 5-10 min or less, it will fire right back up but if you go and eat at a resteraunt or go to walmart and try and leave in 15-45 min later the truck just cranks and cranks and enventually starts but it takes a few tries. I would think that would be fuel related as well. Right? I still have not done the fuel pressure test yet. Bills got in the way of truck parts so next paycheck.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
11-08-10 01:12 PM - Post#2001418    
    In response to tardisguy

OK i finally got a fuel pressure gauge set and I tested the fuel pressure. It is reading only 8 psi before and after the filter with no change as throttle is applied. Im gonna replace the fuel pump this weekend.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
11-08-10 01:42 PM - Post#2001426    
    In response to tardisguy

Looks like chevy tech got it right :D
98 Silverado k1500 4x4 350


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3014

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
11-08-10 02:49 PM - Post#2001459    
    In response to 355Cheyenne

  • 355Cheyenne Said:
Looks like chevy tech got it right :D


Thanks 355Cheyenne!
I still wander by the site once in a while.
It looks like you and Richard are doing a lot of the lifting.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3014

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
11-08-10 02:54 PM - Post#2001463    
    In response to tardisguy

  • tardisguy Said:
OK i finally got a fuel pressure gauge set and I tested the fuel pressure. It is reading only 8 psi before and after the filter with no change as throttle is applied. Im gonna replace the fuel pump this weekend.


There are multiple failures that can causes the TBI trucks to have low fuel pressure other then the fuel pump. It could have a bad fuel pressure regulator or another problem.

As these trucks get older it is becoming a common problem for the rubber hose in the tank between the fuel pump and the sending unit to split. Some people notice when this starts happening the truck will run better with more fuel in the tank.

While you have the fuel gauge on it, stopping the flow in the return line and running the pump momentarily will test to see if a low pressure problem is caused by the regulator. A bad regulator can let the fuel return to the tank instead of maintaining the correct pressure. If restricting flow in the return line, using care not to damage the return line hose, makes a low pressure reading surge well above the specification pressure, then the regulator is the problem.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
tardisguy 
Contributor
Posts: 143

Age: 30
Loc: San Antonio, TX
Reg: 09-15-10
11-29-10 10:15 AM - Post#2011063    
    In response to Chevytech

ok I took chevytech's advice and changed the fuel pressure regulator. That was it. No more surging. It still dies when the engine is cold and stumbles some first drive of the day but I think its the cheap gas I filled up with because I was almost out. Thanks everyone for their help. I appreciate it.
Andrew
91 Chevy C1500 ext cab, TBI 350 auto, 2in suspension lift. (DD)
86 Chevy M C SS, auto 305 with port and polish, Flowtech Afterburner headers, duals to Jegs chambered mufflers (Weekend toy/project)
2012 Mitsu Outlander Sport (wife's DD)


 
Low priced Genuine GM Auto Parts
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