Reading OBD1 codes on my 1990
Thread Starter
Racer
Joined: Mar 1999
Posts: 323
Likes: 0
From: Webster, NY
Reading OBD1 codes on my 1990
Hello, I've been baffled with a problem that I've been having with my car...first of all it's a 1990 with the std. 350 motor and A/T. it has only 11K orig. miles. Aside from the usual problems that plague the C4 with the Bose, inflation restraint light, it's been a good runner. As of recent, the the car after warmed up will start to run rough and lack acceleration and then eventually stall and won't re-start. After sitting it will once again start and go through the same issues. I tried reading the OBD codes and only code it spits out is the 12 code 3x which means that it's in diagnostic mode..........no other codes flash. Don't know where to proceed with this problem as I can't pinpoint the cause of it. One person who owns a '90 told me he had a similar problem and it threw a 14/15 code for an engine coolant temp sensor. Replaced it and it's good again. My car doesn't throw that code at all and no codes at all besides the 12 over and over.....any idea where to proceed at this point. Afraid to drive it to a shop as it may stall out on the road and never get me there......thanks in advance for any ideas.
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
A '90 regardless of miles is generally "assumed" to have injector problems. There's numerous reads throughout the forum regarding checking, reasons for failure BUT if you've no ECM faults, good fuel pressure, good filters and QUALITY fuel it I would believe the first check.
If you've got someone that has serviced it regularly OR is very familiar with early GM PFI you might get a local "evaluation"- a proper "scanner" and familiarity with it a +.
Read more regarding "injectors" etc before moving forward!!
I'm a sales person for no one, I won't don't criticize anyone's recommended procedure for checking BUT I'd suggest that you're evaluating only relevant L98 procedures.
If you've got someone that has serviced it regularly OR is very familiar with early GM PFI you might get a local "evaluation"- a proper "scanner" and familiarity with it a +.
Read more regarding "injectors" etc before moving forward!!
I'm a sales person for no one, I won't don't criticize anyone's recommended procedure for checking BUT I'd suggest that you're evaluating only relevant L98 procedures.
Last edited by WVZR-1; Jun 22, 2016 at 02:25 PM.
Safety Car
Joined: Aug 2013
Posts: 4,429
Likes: 605
From: Minneapolis Mn
Might be of value: how long have you had the car? Is this something new or been doing it a while? Any changes, repairs etc done to the car around the time this started? May sound dumb: have you changed brands of gas lately?
If injectors are suspected, I personally would try a can of Seafoam or GM Topend cleaner in the tank and see if that has any effect after a tank or so of gas.
Just based purely on the description, it does sound like the engine may be starved for gas (as noted). I have heard of and seen (on small engines) where something was plugged in the fuel system where a vacuum started being created in the tank after running a while, effectively starving the engine. It would be interesting to have an in-line pressure gauge to see when it happens if you actually have pressure or not.
If injectors are suspected, I personally would try a can of Seafoam or GM Topend cleaner in the tank and see if that has any effect after a tank or so of gas.
Just based purely on the description, it does sound like the engine may be starved for gas (as noted). I have heard of and seen (on small engines) where something was plugged in the fuel system where a vacuum started being created in the tank after running a while, effectively starving the engine. It would be interesting to have an in-line pressure gauge to see when it happens if you actually have pressure or not.
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
One thing that I see pop up from time to time on this forum is the ignition module, it heats up car dies then cools down and starts again. As soon as the car dies pull a spark plug wire and check for spark.
Thread Starter
Racer
Joined: Mar 1999
Posts: 323
Likes: 0
From: Webster, NY
Re: OBD1 codes on my 1990
I have so far purchased a MAP sensor, an ignition module and will replace them to see if any improvement results.....all good points that seem to point to my symptoms while researching the problem I'm having.
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
Get someone that understands diagnostics and how to use a scanner if necessary and diagnose the issues! The MAP and the IM are likely returnable if still in package, once installed they're yours. If you understand the fuel pressure checking procedure it cost's nothing, a more practical start maybe then "throwing money"!
You can research all you like - BUT - you'd likely be better getting proper diagnostics!
Instructor
Joined: Feb 2008
Posts: 177
Likes: 5
From: Toronto Ontario
Check the resistance of the injectors both hot and cold...should be around 16-17 ohms. It's a cheap and easy procedure. They can test OK cold but fail when hot. If you find any with low resistance you have identified the problem. Fuel containing ethanol degrades the injectors.
Last edited by gmboileau; Jul 11, 2016 at 11:26 PM.
Race Director
Joined: Mar 2015
Posts: 15,926
Likes: 579
When it dies and will not start shoot some fluid in it if it fires it is fuel. If not ele. Then go from there. I would not change any parts yet. Might just cause more confusion. New parts can be bad and you are left chasing your tail.
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