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Newer truck question
#1366854 Sun Jun 28 2020 08:41 PM
Joined: Jul 2009
Posts: 361
5
Shop Shark
I was referred here to ask a few questions about my newer truck. So I have a 1990 3500 454 throttlebody injection. It has a rough idle and pops thru the injection when under full power. I pulled and replaced the plugs, cap,rotor, and sparkplug wires. still does it. once it is off idle (and that is about 1100 rpm it smoothes out and runs fine.In reverse it has more of a rough idle than in forward. plugs looked good when pulled no oil or carbon has 275 k but the motor was rebuilt in 2015 per previous owner. no smoke out the back but exhost has a gas smell to it. Where would be a good place to look next? Or if this is the wrong place just say getouta here. Thanks

Re: Newer truck question
59chevy36 #1366860 Sun Jun 28 2020 09:11 PM
Joined: Apr 2005
Posts: 8,763
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
What codes are you showing at the OBD2 port?


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!

Re: Newer truck question
59chevy36 #1366868 Sun Jun 28 2020 10:17 PM
Joined: Sep 2011
Posts: 710
B
Shop Shark
Just get stabs in the dark without some data & codes. Sounds like going lean, have you checked the fuel filter?


BC
1960 Chevy C10 driver 235 T5 3.73 dana 44
1949 GMC 250 project in waiting
1960 C60 pasture art
G.M dealer tech since 1980 & counting
Re: Newer truck question
59chevy36 #1366878 Sun Jun 28 2020 11:06 PM
Joined: Jul 2009
Posts: 361
5
Shop Shark
I dont have a code reader. but no ck eng lite and i have pulled codes with the old paper clip in the obd port. i have a friend who just bought a reader for newer trucks and it has a adapter that would fit mine . is there any good info to be gained there? will look at fuel filter ,dont think its that old. also had nothing to do this aftn so put a new coil on also. looking at the injectors at idle they are running a lot of gas. to my eyes

Re: Newer truck question
59chevy36 #1366881 Sun Jun 28 2020 11:18 PM
Joined: Apr 2005
Posts: 8,763
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
Run it by your favorite chain auto parts store and get them to print off the codes for you . Free service. Once you get the codes post them here and some of our master mechanics will advise the cure.


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!

Re: Newer truck question
59chevy36 #1366886 Sun Jun 28 2020 11:45 PM
Joined: Dec 2008
Posts: 954
5
Shop Shark
chevytalk.com is a place you can go to for information on your newer Chevy truck.


Brian
My 1955 Truck

My other 1955 Chevy

The older I get the more dangerous I am!!!!!
Re: Newer truck question
59chevy36 #1366904 Mon Jun 29 2020 01:15 AM
Joined: Oct 2005
Posts: 2,924
"Hey! I sound like Darth Vader!!
OBD II didn't happen until 1996 or so. Anything before that was minimal crap that, half the time, you needed to be a NASA scientist to figure out. OBD I might tell you that you have a misfire. OBD II will tell you that you have a misfire and tell you which cylinder it is, along with misfire counts, etc. OBD II data ports have been standardized since the 90's. So, if you need an adapter, you don't have OBD II.

I had a similar issue on my '98 which is a multiport injected engine. I currently have 175,000 miles on it. On my OBD II, it popped up a misfire on 2 of the cylinders. I had done all 8 injectors at about 120,000 because I knew GM had an issue with the OEM's, so in went some better performing Bosch. So, my misfire. Figured, maybe the injectors were going because I had recently done plugs, wires, cap rotor, etc. Replaced all 8 injectors with more new Bosch. Put it all back together (I have a two piece intake, etc.) and my misfire moved to 2 different cylinders. Say what? Did I just put in 2 bad injectors. I tend to be a little OCD on things and numbered the old injectors when they came out. So I pull the mess apart, again. Replace the "misfiring" injectors with 2 known good ones. Guess what? My misfire moved again???? I'm about ready to light a match and end my problems when it occurred to me that my problem could be spark. It shouldn't be because I had all new in there!! What it ended up being is that my distributor gear was soooo worn, it created all kinds of erratic spark issues! That poor gear was just slapping around in there against the cam. I looked in the hole and the cam gear looked good, so in went a new distributor with a metal gear! The original was a plastic/composite/whatever. No more erratic misfire!! No more unburned fuel smell!! No more hiccuping.

If your motor was rebuilt, it's possible they looked at the distributor and, since it looked okay, stuck it back in. But 275K is an awful lot of miles on 2 gears.

Just a thought.

BTW, I'm an ASE MAster Auto and Master Truck with an Undercar Specialist, Truck Equipment Specialist and some School Bus, Body and other stuff thrown in there. Plus a Mobile Hydraulics certification. My company requires this stuff for my job. They even pay for me to take the tests. I never thought much of them. All it meant to me was that I was good at taking tests! I still learn about this stuff every day because the OEM makes new stuff every day. Like how quickly a new F150 will vaporize in a fire because Ferd thought it would be a good idea to make the bodies out of aluminum. I'd share pics, but there really wasn't much to take pictures of.

Re: Newer truck question
MNSmith #1366951 Mon Jun 29 2020 01:02 PM
Joined: Jul 2009
Posts: 361
5
Shop Shark
I wondered about a new distributer. may look on line and see what is around. cant hurt. there is a parts store near will see what they can do with the codes

Re: Newer truck question
59chevy36 #1367059 Mon Jun 29 2020 11:33 PM
Joined: Nov 2000
Posts: 1,909
F
Shop Shark
Since you have a 1990, you have a GMT400 series truck. One active forum for those trucks is https://www.gmt400.com.


Professional Novice
Re: Newer truck question
59chevy36 #1367203 Tue Jun 30 2020 08:14 PM
Joined: Jul 2009
Posts: 361
5
Shop Shark
Well went looking for a distributer. hoping to find a hypo model. nothing showed up. This is a hei with the external coil. also does not have vacuum or centrifical advance. guess the computer does that for me. anyone have good luck with that type ?
which has always bothered me. How does it change the timing? is this a varible cam timing motor?

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