87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust - The 1947 - Present Chevrolet & GMC Truck Message Board Network

93FatBottom · 03-18-2016, 12:19 PM

I recently did my ECT sensor, MAP sensor, checked for vacuum leaks. Checked fuel injectors and they seem to be working well (no leaks or off spray patterns. Currently have no codes popping. If snap my throttle in park, it will act like its ran out of gas for about two seconds and then rev. If I then quickly let go of the throttle it'll pop (very slight backfire) from the exhaust. Truck never fails to start nor does cranking time fluctuate, so I'm pretty confident it's not fuel related. If I drive it under very light throttle it will stall, especially if I let off. I've read O2 sensors can definitely cause these problems but EGR sounds most likely. I'll probably pick up an EGR from Autozone or Napa today. I may do the O2 as well, but i want to look into upgrading to a heated sensor.

Has anyone experienced similar troubles with their TBI 350?

Thanks guys!

allengator · 03-18-2016, 12:32 PM

have you tried cap/rotor/plugs/wires???

68c10owner · 03-18-2016, 12:44 PM

Does the truck have any codes?

Mattchu60 · 03-18-2016, 03:21 PM

I had issues with mine 3 years ago, not the same but similar, would backfire under load. I chased it for probably 3 months, finally gave up and put new wires and cap/rotor on - solved the problem. I also put in a new O2 Sensor and coolant temp sensor before figuring it out, replaced all the vacuum lines, new spark plugs.

Blessed66 · 03-18-2016, 04:46 PM

Quote:

Originally Posted by 93FatBottom

I recently did my ECT sensor, MAP sensor, checked for vacuum leaks. Checked fuel injectors and they seem to be working well (no leaks or off spray patterns. Currently have no codes popping. If snap my throttle in park, it will act like its ran out of gas for about two seconds and then rev. If I then quickly let go of the throttle it'll pop (very slight backfire) from the exhaust. Truck never fails to start nor does cranking time fluctuate, so I'm pretty confident it's not fuel related. If I drive it under very light throttle it will stall, especially if I let off. I've read O2 sensors can definitely cause these problems but EGR sounds most likely. I'll probably pick up an EGR from Autozone or Napa today. I may do the O2 as well, but i want to look into upgrading to a heated sensor.

Has anyone experienced similar troubles with their TBI 350?

Thanks guys!

Try this pretty good YouTube video on troubleshooting. You mention in the title it runs rich, but it "feels" like it's running out of gas when you blip the throttle in park.

I'm currently swapping a TBI into a carb'd truck, and am pretty comfortable with TBI at this point, but if you're not throwing codes, that makes it tougher, but it means you can kinda (but not 100%) rule out sensors. If they were out of range with what the other half dozen sensors are doing, it'd likely pop a code.

An EGR valve could be an issue (See here) so it's something to check. Basic plugs, wires, cap, rotor. Check the little things first.

87 STEPPER · 03-18-2016, 08:17 PM

I'd ck the vacuum lines goin to the EGR and all of 'em for that matter then I'd remove the EGR line from the manifold side and either use a vac pump if u have 1 or just suck it! The EGR should move to the open position and return to closed by spring pressure when u quit suckin'

If it works leave it alone maybe ck the EGR mount gasket for leaks.

There is one other thing that can cause a similar problem like yours and that is the fuel pressure regulator it may have a ruptured diaphragm or a broke or week return spring.

Good luck.

2manycars2littletime · 03-18-2016, 09:58 PM

In addition to the above recommendations, I would check the Throttle Position Sensor too.

cadillac_al · 03-19-2016, 10:10 AM

With no codes I would look at fuel pressure, vacuum and timing. Those things aren't monitored by the ECM. Could be ECM too.

93FatBottom · 03-22-2016, 08:46 AM

Thank you so much guys! You've given me a major head start!

No codes at this time, cap/rotor plugs/wires were done in September.

My dad wants me to check the coil.

I pulled the EGR off and cleaned it and the port and blew it out with air and put it on with a new gasket and now it's no no where near as bad but still noticeable.

Still driving the truck daily.

ZacharyDouglas1992 · 03-22-2016, 11:23 AM

try unplugging your EGR valve altogether and running it that way. You will get the CEL to come on after a while, but if it runs way better other than that, you'll know what the problem is. That is how I was able to diagnose mine.

other than that - it sounds like you could have a timing advance or fuel pressure issue.

93FatBottom · 03-25-2016, 09:43 AM

So I ran it with no EGR, seemed to run a little better, but I finally popped a SES light. Low voltage at TPS, DTC 22...

lkfldredneck · 03-25-2016, 11:47 AM

Have you checked the Coolant temperature sensor that is ontop of the intake?

i had a 94 TBI that had the same kinda problem. Couldnt figure it out, i replaced everything, EGR sensor, o2 sensor, etc. and the problem ended up being the coolant temperature sensor.

When that sensor goes it doesnt throw any codes and it acts like it is trying to start in extreme cold weather (Something like -80) and just dump fuel into it making it run rich and stumble and so on.

03-18-2016, 12:19 PM	#1
93FatBottom Registered User Join Date: Jul 2011 Location: Simi Valley, CA Posts: 80	87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust I recently did my ECT sensor, MAP sensor, checked for vacuum leaks. Checked fuel injectors and they seem to be working well (no leaks or off spray patterns. Currently have no codes popping. If snap my throttle in park, it will act like its ran out of gas for about two seconds and then rev. If I then quickly let go of the throttle it'll pop (very slight backfire) from the exhaust. Truck never fails to start nor does cranking time fluctuate, so I'm pretty confident it's not fuel related. If I drive it under very light throttle it will stall, especially if I let off. I've read O2 sensors can definitely cause these problems but EGR sounds most likely. I'll probably pick up an EGR from Autozone or Napa today. I may do the O2 as well, but i want to look into upgrading to a heated sensor. Has anyone experienced similar troubles with their TBI 350? Thanks guys!

03-18-2016, 12:32 PM	#2
allengator Registered User Join Date: Dec 2010 Location: Burleson, Texas Posts: 596	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust have you tried cap/rotor/plugs/wires??? __________________ Allengator Outta the Blue (my band - available for hire in the DFW area!) 1980 Chevy SWB Pickup (build thread) 1951 Chevy Sedan Delivery 2004 Chevy Tahoe Z71 2011 Harley Davidson Street Glide 2018 Silverado Z71 Crew Cab

03-18-2016, 12:44 PM	#3
68c10owner Registered User Join Date: Oct 2003 Location: Carmichael, California Posts: 3,011	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust Does the truck have any codes? __________________ Anthony

03-18-2016, 03:21 PM	#4
Mattchu60 Registered User Join Date: Jan 2014 Location: Swaledale, IA Posts: 485	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust I had issues with mine 3 years ago, not the same but similar, would backfire under load. I chased it for probably 3 months, finally gave up and put new wires and cap/rotor on - solved the problem. I also put in a new O2 Sensor and coolant temp sensor before figuring it out, replaced all the vacuum lines, new spark plugs.

03-18-2016, 08:17 PM	#6
87 STEPPER STILL PLAYS WITH TRUX Join Date: Nov 2002 Location: Melbourne, Fla. Posts: 2,764	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust I'd ck the vacuum lines goin to the EGR and all of 'em for that matter then I'd remove the EGR line from the manifold side and either use a vac pump if u have 1 or just suck it! The EGR should move to the open position and return to closed by spring pressure when u quit suckin' If it works leave it alone maybe ck the EGR mount gasket for leaks. There is one other thing that can cause a similar problem like yours and that is the fuel pressure regulator it may have a ruptured diaphragm or a broke or week return spring. Good luck. __________________ ~~Bruce~~ MY 87 STEPPER MY 99 2D/WD TAHOE

03-18-2016, 09:58 PM	#7
2manycars2littletime Registered User Join Date: Feb 2016 Location: Troy MI Posts: 14	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust In addition to the above recommendations, I would check the Throttle Position Sensor too. __________________ Keep your head up...and your stick on the ice.

03-19-2016, 10:10 AM	#8
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,378	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust With no codes I would look at fuel pressure, vacuum and timing. Those things aren't monitored by the ECM. Could be ECM too. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

03-22-2016, 08:46 AM	#9
93FatBottom Registered User Join Date: Jul 2011 Location: Simi Valley, CA Posts: 80	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust Thank you so much guys! You've given me a major head start! No codes at this time, cap/rotor plugs/wires were done in September. My dad wants me to check the coil. I pulled the EGR off and cleaned it and the port and blew it out with air and put it on with a new gasket and now it's no no where near as bad but still noticeable. Still driving the truck daily.

03-22-2016, 11:23 AM	#10
ZacharyDouglas1992 Registered User Join Date: Nov 2013 Location: Fowler California Posts: 140	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust try unplugging your EGR valve altogether and running it that way. You will get the CEL to come on after a while, but if it runs way better other than that, you'll know what the problem is. That is how I was able to diagnose mine. other than that - it sounds like you could have a timing advance or fuel pressure issue. __________________ 1967 CHEVELLE MALIBU 427/700R4 1971 CHEYENNE 10 350/350 1983 GMC K3500 454/400/205 1987 R10 TBI 350/700R4 2014 CRUZE 2.0 TURBO DIESEL

03-25-2016, 09:43 AM	#11
93FatBottom Registered User Join Date: Jul 2011 Location: Simi Valley, CA Posts: 80	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust So I ran it with no EGR, seemed to run a little better, but I finally popped a SES light. Low voltage at TPS, DTC 22...

03-25-2016, 11:47 AM	#12
lkfldredneck Registered User Join Date: Jan 2016 Location: Ontario Posts: 123	Re: 87 TBI 350 runs rich, stalls, stumbles, slight backfire out exhaust Have you checked the Coolant temperature sensor that is ontop of the intake? i had a 94 TBI that had the same kinda problem. Couldnt figure it out, i replaced everything, EGR sensor, o2 sensor, etc. and the problem ended up being the coolant temperature sensor. When that sensor goes it doesnt throw any codes and it acts like it is trying to start in extreme cold weather (Something like -80) and just dump fuel into it making it run rich and stumble and so on.



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