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Stalling 1987 G20 #748897
May 26th 2019 1:37 am
May 26th 2019 1:37 am
Joined: Sep 2016
Posts: 14
USA
G
gmcsmb Offline OP
stranger
gmcsmb  Offline OP
stranger
G
Joined: Sep 2016
Posts: 14
USA
I can't figure out why my van keeps stalling. It's a TBI 5.7 with a 700r4.

The engine shuts off at low rpm, with a light load though it's also shut off on me while coasting downhill--not fun. Lately it happens more when I'm parallel parking and turn the steering wheel. The van also seems to lack power. It failed a few smog checks with high NOX and HC. I figured the van was running lean and have already replaced the fuel filter, EGR valve and solenoid, and o2 sensor. I checked the fuel pressure near the filter and it was around 11psi at idle.

Not sure if this is related, but after driving for a bit and shutting the engine off, restarting is weird. Like the engine is skipping. I don't really know how to explain it.

I have a scanner and a vacuum gauge. Do any members who are experienced with repairing this engine have suggestions for things to test?

Re: Stalling 1987 G20 [Re: gmcsmb] #748899
May 26th 2019 2:17 am
May 26th 2019 2:17 am
Joined: Jun 2010
Posts: 14,301
Van Diego California
frscke1 Offline
frscke1  Offline

Joined: Jun 2010
Posts: 14,301
Van Diego California
Clogged exhaust .... no air thru stalls out


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Re: Stalling 1987 G20 [Re: gmcsmb] #748911
May 26th 2019 4:04 pm
May 26th 2019 4:04 pm
Joined: Nov 2013
Posts: 3,393
Michigan
Dyno_Dave Offline
pooh-bah
Dyno_Dave  Offline
pooh-bah
Joined: Nov 2013
Posts: 3,393
Michigan
You'll have to do some diagnosis.

TBI is fuel pressure sensitive. It likes to be in the 11-13 pound range, higher the better. If it's getting weak, then it will run poorly, be hard to start, etc.

An ignition module in the distributor that is failing can also act this way.

Re: Stalling 1987 G20 [Re: frscke1] #749134
May 31st 2019 5:06 pm
May 31st 2019 5:06 pm
Joined: Sep 2016
Posts: 14
USA
G
gmcsmb Offline OP
stranger
gmcsmb  Offline OP
stranger
G
Joined: Sep 2016
Posts: 14
USA
Frscke,

I attempted to check my backpressure with a vacuum gauge connected to manifold vacuum. At idle and holding around 3000 rpm vacuum was steady at 20in/Hg. If I can find the time and parts I'll try to rig a fitting into the o2 sensor bung to measure the actual psi in the exhaust, but it doesn't look like a clogged exhaust is the problem so far.

Re: Stalling 1987 G20 [Re: Dyno_Dave] #749185
June 02nd 2019 9:57 pm
June 02nd 2019 9:57 pm
Joined: Sep 2016
Posts: 14
USA
G
gmcsmb Offline OP
stranger
gmcsmb  Offline OP
stranger
G
Joined: Sep 2016
Posts: 14
USA
Dave,

I need to rig a way to connect my fuel pressure test kit closer to the TBI so that I can monitor the fuel pressure while driving and under load. The problem is intermittent, which I should have mentioned sooner. I'm not sure what might cause and intermittent fuel pressure drop. Bad ground or something?

Do you know of a way to test this ignition module in the distributor?

Re: Stalling 1987 G20 [Re: gmcsmb] #749193
June 03rd 2019 12:27 pm
June 03rd 2019 12:27 pm
Joined: Mar 2011
Posts: 341
NY
J
jcd74 Offline
enthusiast
jcd74  Offline
enthusiast
J
Joined: Mar 2011
Posts: 341
NY
Quick way to check for a clogged exhaust is to pull the 02 sensor, runs better restricted exhaust.

Re: Stalling 1987 G20 [Re: gmcsmb] #749225
June 03rd 2019 8:52 pm
June 03rd 2019 8:52 pm
Joined: Nov 2013
Posts: 3,393
Michigan
Dyno_Dave Offline
pooh-bah
Dyno_Dave  Offline
pooh-bah
Joined: Nov 2013
Posts: 3,393
Michigan
I have one of these, but I didn't pay this much for it. I planned to leave mine installed permanently, and add a small gauge.

EBAY

When the pump went on my '95, it was intermittent. Worse hot.

I don't know if parts stores have a tool that can check those modules or not.

Re: Stalling 1987 G20 [Re: gmcsmb] #749360
June 08th 2019 4:59 pm
June 08th 2019 4:59 pm
Joined: Jan 2006
Posts: 59
NC
C
CBnNC Offline
journeyman
CBnNC  Offline
journeyman
C
Joined: Jan 2006
Posts: 59
NC
I had similar issue with my G3500. Cleaning the Idle Air Control (IAC) and passages helped it. Also getting out on highway and running along at 70 mph got it breathing better.


'89 GMC 1 ton Ralley STX

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