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1993 K1500 TBI stumbling/surging #4547652
10/18/17 08:51 PM
10/18/17 08:51 PM
Joined: Feb 2015
Posts: 710
Sask, Canada
BrianF Offline OP
BrianF  Offline OP
Joined: Feb 2015
Posts: 710
Sask, Canada
Well a few months back I picked up a 93 GMC 1500 2 wheel drive rez truck from a friend. 370,600km on the clock and V8. Its got a few problems but otherwise is a decent truck for what I need it for. I replaced the brake switch and got the TCC locking up again but have to chase a low speed surge/stumbling problem. The hose that routes the PCV to the throttle body was rotten so I have that plugged for now. But the main issue is this: once the engine is up to temp it stumbles from idle until around 1500rpm and then it levels out and drives fine on the highway and pulls great through the rev range. It idles fine but once you tip in that is where it stumbles. It never dies.

When it is cold it starts and runs fine. Because of this I was thinking oxygen sensor first. Thinking closed/open loop operation.

Any thoughts?

Thanks!


2006 Trailblazer LT. Castrol Edge with Fram Ultra.
2017 Ram 3500 SLT Megacab. Duron SHP 10w30 with Hastings LF608.
1993 GMC 1500. It has oil and still runs
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547657
10/18/17 08:57 PM
10/18/17 08:57 PM
Joined: Sep 2015
Posts: 1,529
USA
mk378 Online content
mk378  Online Content
Joined: Sep 2015
Posts: 1,529
USA
Throttle position sensor, check it with a voltmeter. Also check that the tubing from the MAP sensor to the intake is intact.

Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547671
10/18/17 09:08 PM
10/18/17 09:08 PM
Joined: Aug 2008
Posts: 18,659
Ontario, Canada
StevieC Online content
StevieC  Online Content
Joined: Aug 2008
Posts: 18,659
Ontario, Canada
Could also be a coil / wires breaking down or leaking spark at specific times. But check the TPS first.


'18 Highlander - AMSOIL SS 0w20 / ATF / Severe Gear
'06 Santa Fe - 535,000km AMSOIL SS 0w30 / ATF (R.I.P)
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547759
10/18/17 11:33 PM
10/18/17 11:33 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
It's acting like the accelerator pump is not squirting when the engine is coming off idle, but this engine is throttle body injected; no carburetor. Hmm...

Re: 1993 K1500 TBI stumbling/surging [Re: StevieC] #4547762
10/18/17 11:37 PM
10/18/17 11:37 PM
Joined: Feb 2013
Posts: 10,712
Phoenix, AZ
Nick1994 Online content
Nick1994  Online Content
Joined: Feb 2013
Posts: 10,712
Phoenix, AZ
Originally Posted By: StevieC
Could also be a coil / wires breaking down or leaking spark at specific times. But check the TPS first.
+1


2015 Hyundai Sonata 2.4L 84k Mobil 1 AFE 0w30 & OEM
2000 Toyota Camry 2.2L 230k Valvoline 5w30 & Fram Ultra
1996 Jeep Cherokee 4.0L 147k Mobil 1 HM 10w40 & Fram Ultra
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547855
10/19/17 05:17 AM
10/19/17 05:17 AM
Joined: Nov 2007
Posts: 258
Richmond, VA
DNVDMAX Offline
DNVDMAX  Offline
Joined: Nov 2007
Posts: 258
Richmond, VA
Disconnect the EGR and plug any tubing you disconnected in the process. See if this helps. If so, I can be the EGR, cracked tubing, or the control solenoid.

Carbon may also prevent the EGR from fully seating. After doing the above, I'd also manually manipulate the EGR diaphragm through the slots to check if it's stuck.


06 GMC 2500HD DMAX EFILIVE M1 TDT 5w-40 FRAM Ultra
91 GMC K1500 5.7L 5w-30 Quaker State HM Bosch D+
72 Nova 350 SBC 74mm AirWerks Turbo 15w-40 HDEO
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547879
10/19/17 06:08 AM
10/19/17 06:08 AM
Joined: Dec 2009
Posts: 5,046
Tn.
CourierDriver Offline
CourierDriver  Offline
Joined: Dec 2009
Posts: 5,046
Tn.
A 24 yr old ride has a right to be stumbling at that age,,lol


Forks Over Knives Official Plant-Based Group check it out on facebook
Re: 1993 K1500 TBI stumbling/surging [Re: CourierDriver] #4547901
10/19/17 06:43 AM
10/19/17 06:43 AM
Joined: Aug 2010
Posts: 5,685
Champlain/Hudson Valley
Kira Offline
Kira  Offline
Joined: Aug 2010
Posts: 5,685
Champlain/Hudson Valley
Spent A LOT of time attempting to diagnose a friend's '89 K1500.
The engine sputtered badly. No real telling if higher revs changed anything though there was some smoothing at speed.
The symptoms pointed to fuel delivery and/or spark management.

THE FIX: Turns out there was a built in tap off on the battery cable (big red one) coming from the clamp. It powered the nascent fuel controller (the flat black 4" X 5" thing held by a bracket right near the throttle body-don't know about '93). The lead swaging of the clamp was full of lead oxide. A new cable fixed all our ills.

FYI: The "computer part for the ignition" was housed in a compartment which was a bulge. Half of this bulge was the back of the glove compartment and the other half reached into the engine bay. The firewall was bulged to accommodate it.

Hope tis helps.

Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547940
10/19/17 07:43 AM
10/19/17 07:43 AM
Joined: Aug 2005
Posts: 907
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 907
dayton oh
this one is a classic failure.pcv system blocked caused the blowby to enter the tbi through the vent.
rots the fpr spring and drops fuel pressure.
the tbi baseplate passages plug with crud.
clean it up and rebuild the fpr first.
do not plug off the pcv!
fix it.
also make sure the sensor ground cluster at the water outlet is clean and tight.
these 2 things account for the lions share of problems.

Re: 1993 K1500 TBI stumbling/surging [Re: Kira] #4547960
10/19/17 07:58 AM
10/19/17 07:58 AM
Joined: Aug 2005
Posts: 907
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 907
dayton oh
that black module is the esc.
fuel management is in the ecm.
loss of power via that battery tap will indeed cause lots of issues.
Originally Posted By: Kira
Spent A LOT of time attempting to diagnose a friend's '89 K1500.
The engine sputtered badly. No real telling if higher revs changed anything though there was some smoothing at speed.
The symptoms pointed to fuel delivery and/or spark management.

THE FIX: Turns out there was a built in tap off on the battery cable (big red one) coming from the clamp. It powered the nascent fuel controller (the flat black 4" X 5" thing held by a bracket right near the throttle body-don't know about '93). The lead swaging of the clamp was full of lead oxide. A new cable fixed all our ills.

FYI: The "computer part for the ignition" was housed in a compartment which was a bulge. Half of this bulge was the back of the glove compartment and the other half reached into the engine bay. The firewall was bulged to accommodate it.

Hope tis helps.

Re: 1993 K1500 TBI stumbling/surging [Re: kc8adu] #4547967
10/19/17 08:03 AM
10/19/17 08:03 AM
Joined: May 2012
Posts: 2,500
Indiana
Phishin Offline
Phishin  Offline
Joined: May 2012
Posts: 2,500
Indiana
Originally Posted By: kc8adu
this one is a classic failure.pcv system blocked caused the blowby to enter the tbi through the vent.
rots the fpr spring and drops fuel pressure.
the tbi baseplate passages plug with crud.
clean it up and rebuild the fpr first.
do not plug off the pcv!
fix it.
also make sure the sensor ground cluster at the water outlet is clean and tight.
these 2 things account for the lions share of problems.


I agree with this. My 1990 K1500 has the 350TBI....and this fixed many of my problems as well.

The PCV on these things really tends to plus in the TB. I'd go to NAPA and get a TB rebuild kit. Take the TB off, clean it all up, replace the FPR diaphram and all the seals and gaskets and make sure the PCV port is cleaned really well. This shouldn't take you too long, it's kind of fun because it's all so easy, and you'll know from now on you don't have a fuel problem.


2018 Chevy Silerado 3500HD 6.0L Gas: RLI 10w30
2010 Accord-LX K24: VSP 0w20/MaxLife 10w30 + LG BioTech HD
2014 CR-V LX K24: M1 0w30
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4547984
10/19/17 08:22 AM
10/19/17 08:22 AM
Joined: Aug 2005
Posts: 907
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 907
dayton oh
hopefully all the kits have the spring now.
many in the past did not.most common failure part and not in the kit.stupid.

Re: 1993 K1500 TBI stumbling/surging [Re: kc8adu] #4548002
10/19/17 08:39 AM
10/19/17 08:39 AM
Joined: May 2012
Posts: 2,500
Indiana
Phishin Offline
Phishin  Offline
Joined: May 2012
Posts: 2,500
Indiana
Originally Posted By: kc8adu
hopefully all the kits have the spring now.
many in the past did not.most common failure part and not in the kit.stupid.


Mine didn't have a spring...this was the kit from Napa about 4-5 years ago.

I cleaned up the spring the best I could. I then put some light grease on it to prevent it from rusting. Since the spring "might" have been "tired" and lost some of it's function, I put a single US $0.25 Quarter in the throttle body to act as a spacer for the spring to give it a bit more force onto the FPR.


2018 Chevy Silerado 3500HD 6.0L Gas: RLI 10w30
2010 Accord-LX K24: VSP 0w20/MaxLife 10w30 + LG BioTech HD
2014 CR-V LX K24: M1 0w30
Re: 1993 K1500 TBI stumbling/surging [Re: BrianF] #4548561
10/19/17 06:17 PM
10/19/17 06:17 PM
Joined: Aug 2005
Posts: 907
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 907
dayton oh
the $0.25 mod is a common way to boost fuel pressure a bit.
as for the spring most are in at least 2 pieces when i see them.the blowby backing up due to no vacuum on pcv blows right on it and rots it fast.
drive too long like this and the engine will sludge up.

Re: 1993 K1500 TBI stumbling/surging [Re: kc8adu] #4551662
10/23/17 06:35 AM
10/23/17 06:35 AM
Joined: May 2012
Posts: 2,500
Indiana
Phishin Offline
Phishin  Offline
Joined: May 2012
Posts: 2,500
Indiana
Originally Posted By: kc8adu
the $0.25 mod is a common way to boost fuel pressure a bit.
as for the spring most are in at least 2 pieces when i see them.the blowby backing up due to no vacuum on pcv blows right on it and rots it fast.
drive too long like this and the engine will sludge up.


kc8adu: No doubt. When I bought my truck, it was a sludge MONSTER. I took the VC's off and scooped the crusty nasty crud out. Several times I filled the engine with kerosene and sometimes a mix of kerosene and toluene, disconnected the dizzy cap and would would crank it over for 15-20 second burst several times through out the day for several days. Drain and refill.

I bought my K1500 with 150k miles for $1800. I've put over 60k miles on her. She's still running decent.


2018 Chevy Silerado 3500HD 6.0L Gas: RLI 10w30
2010 Accord-LX K24: VSP 0w20/MaxLife 10w30 + LG BioTech HD
2014 CR-V LX K24: M1 0w30
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