350 TBI Idles well, but pretty much dies otherwise...HELP! - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 04-09-2010, 12:20 PM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
350 TBI Idles well, but pretty much dies otherwise...HELP!

My 350 TBI in my truck is becoming undriveable with a really bad bog and hesitation/stumble when I try and take off at any rpm or speed. It's pretty much always there, I can get it to behave a bit once I'm moving but that's really only between 20 and 40 mph and that's by hitting the sweet spots.

I've read a lot in the past few days on different forums of people with similar issues, a lot were fuel pressure related, some TBI gasket etc.

All these guys threw a lot of parts at their cars before solving the issue as what they did was just speculation and seems to me they wasted a bunch of money. I'd like to avoid that and hope you guys can help. I've tried to include all the info I can think of, let me know what you think and if any other info is needed.

History:

Engine was put in aprox 9 years ago, came out of a early 90's van/truck, it's clean and looks like a lot was replaced when it was swapped in. Truck pretty much sat the last 7 years and I bought it 2 months ago.

When I picked it up it started fine had lots of power.

The next day it was idling and just cut out, it started doing that consistently after idling for more than 3 or 4 minutes once it was in closed loop.

It also developed a bad bog/stutter/lean backfire on the highway, especially uphill, the heavier the load the worse it was. In open loop idled fine, closed loop it would hunt between 2 idle speeds.

The lean backfire is gone since I replaced the coolant temp sensor and it idles fine now too.

Vehicle specs:


'84 K30 pickup with manual gearbox and 90's TBI engine (low miles, driven very little so I'm told, the moss was tell tale sign...)

2 into 1 exhaust, single muffler NO cat.

350 TBI no mods all stock w/ smog pump, EGR everything (I don't like these things...)

It used to be a diesel so the brakes run of the power steering pump so no vac. booster/hoses to worry about either.

I run it in 2wd

It's always been a hard starter taking between 8 and 12 revolutions of the engine before it catches. Doesn't almost catch either, once it starts it starts directly just takes it turning over about 5 or 6 seconds, warm or cold.

Once idling in Neutral it doesn't smell rich, with my nose in the tailpipe it seems fine.


Symptoms:

Idles quite smoothly, runs about 1100 RPM at startup and after 2 minutes or so settles around 850RPM.

If I try and take off it falls flat on it's face, by babying it with lots of throttle and little increments of clutch I can get it to go, barely. Can't get much past 3k RPM as it start to bog badly and the lower the RPM the more it wants to quit and will just die, but clutch in, no load it idles just fine. It will however backfire occasionally and stall occasionally when I'm trying to get it to go, I think it's flooding. There's no carb backfire.

If I try and give it more gas it just get's worse and every so often it will give a big backfire out the exhaust, like small arms loud!

It's pretty much undriveable. But idles fine and moves through the rev range perfectly in Neutral. I can apply the throttle any way I like and it responds well: gradual build up, Idle to WOT etc. Nothing seems to phase it then...

It started as a boggy/misfire uphill on the highway and has gotten worse and now won't take off from a stand still without babying and even then it will stall and misbehave.

What I've done so far:

Replaced Coolant Temp Sensor as readings showed it was faulty. Hoped this was the issue, it did solve a hunting Idle issue and intermittent cut out issue but that's all (it used to just switch off after about 3 minutes of idling but is fine now)

Checked the EGR by hand, it moves but has resitance, no vacuum at idle (so EGR controller should be ok)

Should the EGR move completely freely or have some resistance?

Checked for vacuum leaks by spraying all around TBI base and all vacuum hoses with starter fluid none to be found. Also did visual inspections no obvious cracks or damaged lines.

Replaced PCV, old one was a bit sticky.

Smog pump is pumping air in.

Inspected injectors both are pulsing well at idle and when given throttle in Neutral seem to spray evenly.

On the to do list:

Check and replace if necessary:

Plugs, wires, cap and rotor.

Check voltage on TPS (what max voltage should it give?)

Check fuel pressure (9-13psi right?)

Suggestions?

Could the TPS even be faulty as in Neutral it's fine all along the RPM band...

Whatever I can scrap to make this thing simpler and rule potential problems out I'm all for, no emissions laws applicable to this vehicle where I live

Look forward to hearing your thoughts on this as it's driving me CRAZY!!!!!!!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-10-2010, 08:41 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I've since checked the EGR again, it moves freely hot or cold.

Cap and rotor are in good shape.

Timing is right on.

It's an 87 TBI motor btw I found out today.

Also after simply checking all of these things today it ran fine. Dah!

From a cold start for about 5-10 minutes it ran fine and then behaved like before, stalling, stumbling and starting really hard after stalling.

Got it back home, checked all I mentioned before, ran about a 3 mile test run, all was fine again with one minor hesitation around 2500rpm that happened once...

What gives?!
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-10-2010, 02:38 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 57
Posts: 5,181
Wiki Edits: 26

Thanks: 7
Thanked 111 Times in 96 Posts
I would take the EGR off and clean it to make sure it is closing all the way. Since you messed with it and it was ok for a short while, it may be all carboned up. This could be due to the bad coolant temp sensor, if it was running rich for any length of time. The TPS is not a real common failure item and doesnt usually exhibit the symptoms you are describing.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 01-27-2011, 12:20 PM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Bump.

Just wanted to try and revive this. The truck sat unused due to this issue it's really random and I'd like to get this fixed.

Any help would be apreciated.

Again to summarize:

Starts fine cold, runs for a while (does seem to miss a bit of power under load but it's hard to compare as it has a lowly geared manual) then every so often it just shuts off when idling at a stoplight or whatever. It has sputtered a lot on the highway too.

When it dies it will start right up, seems like if I try and give it gas that makes starting harder and it won't catch as quickly, perhaps flooding.

Otherwise see my first post.

Thanks!
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 02-25-2011, 11:26 AM
Registered User
 
Join Date: Feb 2011
Location: There
Posts: 1
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I had this exact same problem with my 93 TBI engine. After checking nearly everything you did and some other things, I finally checked my fuel pressure with a T fitting at the fuel filter. It was only running around 9 psi. VERY VERY LOW. But it idled fine and would die out if I gave it much gas.

With that said, that leaves 2 things. The fuel pressure regulator in the TBI and the fuel pump. Mine was the fuel pump. And while I was in there, I went ahead and finally fixed my gas gauge by replacing the fuel sending unit.

Hope this helps you.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 02-25-2011, 11:36 AM
adantessr's Avatar
'23 T-Bucket Pickup
 
Last wiki edit: Troubleshooting ignition Last photo:
Join Date: Jun 2010
Location: South Charleston , WV
Age: 62
Posts: 1,549
Wiki Edits: 3

Thanks: 43
Thanked 17 Times in 15 Posts
Used to be a diesel

You most likely need to change the fuel pump in the tank to the pump that is required for that engine. You very well could have low fuel pressure .
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 02-25-2011, 11:41 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks guys, I'll check the fuel pressure.

I'm pretty sure the pump is the correct one for the engine as it used to be a diesel with a mechanical pump. they changed the motor and tank from a different truck.

I'll post results of fuel pressure.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-04-2011, 04:19 PM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Allright, finally got around to checking the fuel pressure.

It's fine, 12PSI

engine will just cut out, like turning the key off, after running for a few minutes. It will start right up again after cranking 3 to 4 seconds, almost like a cold start.

I can keep it running if I feather the throttle and keep the idle a bit higher when I anticipate it dying.

While driving it still randomly bogs and sputters, more so under hard acceleration.

thanks in advance,
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-08-2011, 01:56 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Can anyone weigh in here or perhaps advise of a place with more comprehensive TBI knowledge/experience?

thanks
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 05-08-2011, 03:34 AM
Registered User
 
Join Date: Apr 2011
Location: new york
Posts: 11
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
thanks guys
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 05-08-2011, 03:54 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by caaraa
thanks guys
Say what now?
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 05-08-2011, 04:19 AM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,657
Wiki Edits: 0

Thanks: 15
Thanked 59 Times in 56 Posts
Even so I`m not sure if this is related to your issue or not it maybe worth checking into. TBI engines have a really bad habit about carboning up severly in the lifter valley and the throttle body, so severe it can completely clog up the ports. When you said the truck sat for a given amount of time that threw a flag up. after it`s long nap when it was started again was it ran at high idle of around 1800 RPM for 20 minutes? If not the cam could be going flat. Chevy`s that sit are bad about eating the cams if the engine isn`t cycled.
You could yank both valve covers, let it idle and see if you see any rockers barely moving compared to the rest, if so the cam is history. Another thing I`ve thought of is since the truck sat, there could be trash in the fuel tank, even so you checked it and it read 12 psi, if the sock is picking up trash, it`ll run the way you discribed. Last place I`d check would be the ignition system. Get a spark tester and get a look at the spark, if it`s yellow it`s weak, if it`s blue it`s okay.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 05-08-2011, 05:22 AM
willowbilly3's Avatar
Member
 

Last journal entry: Body mods
Last photo:
Join Date: Jun 2004
Location: Black Hills, South Dakota
Age: 61
Posts: 1,208
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Have you put a vacuum gauge on it? Sounds to me like it might possibly be a plugged cat. If the vac gauge goes right to normal then starts backing down it would indicate high back pressure, or you could use a back pressure gauge but not many people have one of those.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 05-08-2011, 09:31 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: NL
Posts: 138
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by willowbilly3
Have you put a vacuum gauge on it? Sounds to me like it might possibly be a plugged cat. If the vac gauge goes right to normal then starts backing down it would indicate high back pressure, or you could use a back pressure gauge but not many people have one of those.

I haven't and will (put a vac. gauge on)...

Good thinking, i.e.: idling it builds up backpressure and cuts out, driving/cruizing it builds up too but not enough to kill it?

This is an interesting new avenue to check. Thanks!

@ DoubleVision:

More solid ideas! Crap in the sock could mess with fuel delivery maybe even dropping pressure intermittently causing a shut off and obviously get screwy under load and poor spark speaks for itself although the cap rotor and wires are good but worth checking again! I now have a to do list with new hope, we shall see. Once I know whatsup I'll post it, nothing worse than an open ended thread.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 05-08-2011, 10:09 AM
Registered User
 
Join Date: Jan 2010
Location: The clouds
Posts: 27
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
When it quits and fails to start pull the air cleaner and see if the tbi is squirting fuel. This should tell you whether it's fuel or spark you're chasing.
However my first thought is the module in the distributor or the pick up coil. Check the distributor bushings by trying to wiggle the shaft side to side with the cap off. These tbi's are famous for a bad distributor and or module
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Goodwrench 350 w/ TBI BadHabitSS Engine 17 07-27-2007 11:37 AM
87' 350 tbi.. out of truck.. chevelle4542speed Engine 1 05-29-2007 10:40 PM
91 rs tbi 305 to 350 carbed tat2 Engine 2 05-15-2004 06:46 PM
305 tbi into an older 350? help... NOSBOSS Engine 2 03-23-2004 09:45 PM
rebuilt 350 TBI running rough warlok Engine 9 11-24-2003 07:02 PM


All times are GMT -6. The time now is 10:30 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.