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Username Post: Mostly a no start, or very rough idle.        (Topic#356856)
johnboy1022 
Poster
Posts: 38
johnboy1022
Reg: 08-14-15
06-17-19 07:56 AM - Post#2768662    

Changed fuel filter, pump is good. Truck was running fine until it wasn't. It was running pretty good. I still have spark and am getting fuel. The engine will crank, but won't start most of the time. If it does start, it will idle very low and rough and eventually kill. I've seen this issue on youtube as a no spark thing, but I do have spark. My distributor and rotor are new. This is a 1990 c1500 TBI 383 build. Pulling the O2 sensor or disconnecting the computer results in no change. The IAC is brand new as well. Any tips for saving me some time on this? "Service Engine Soon" light was on, but I only got a code 12.



 
rittercon 
Silver Supporting Member
Posts: 73
rittercon
Loc: California
Reg: 06-19-18
06-17-19 11:19 AM - Post#2768689    
    In response to johnboy1022

  • johnboy1022 Said:
Truck was running fine until it wasn't...
… My distributor and rotor are new...


Any connection between installing the new parts and the sudden idle issues? In a recent post someone inadvertently switched the #1 and #3 plug wire positions on the distributer cap.



 
johnboy1022 
Poster
Posts: 38
johnboy1022
Reg: 08-14-15
06-17-19 01:11 PM - Post#2768698    
    In response to rittercon

None I could tell. It was low on gas, like really low. It kinda choked but started up and I took it to the gas station and filled up. After the fill up it choked a little more, but started up and ran fine until I got home. Then it started the rough idle. I decided a break was in order. A week later it is almost impossible to start, and if it does, I get the low idle death march. I'll double check the plugs when I get home to make sure. The only recent work that has been done was changing the valve cover gasket, oil, and filter. Took it for a spin after that though and it ran fine.



 
bowtie44s 
Valued Contributor
Posts: 4237
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
06-17-19 07:04 PM - Post#2768723    
    In response to johnboy1022

It will flash the code 12 three times before it goes to the first trouble code. It will flash that one three times before going to the next. When you get a 12 again you know you've got them all.

If you have good blue spark, check your fuel pressure. Just because you're getting some fuel doesn't mean you're getting enough.

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Skribble93 
Poster
Posts: 57

Age: 34
Loc: Upstate NY
Reg: 02-03-18
06-19-19 01:47 PM - Post#2768838    
    In response to johnboy1022

Just a thought have you checked the coolant temp sensor in the intake? Mine has had close to the same symptoms a few times and got worse the closer it got to operating temp and wound up being a bad sensor each time one was new and wound up being faulty from the start quick and cheap fix just a suggestion is all.

If it's to loud your to old

93 K1500 Z71 step side ext/cab 5.7 shorty headers and 3in true duals. 3in body lift and leveling kit.


89 K1500 4.3 rotted frame dubbed parts rig Sold


 
johnboy1022 
Poster
Posts: 38
johnboy1022
Reg: 08-14-15
07-15-19 06:40 PM - Post#2770785    
    In response to Skribble93

I will take a look at that. I did have a small coolant leak shorty before this problem started and had to replace the heater core hoses. I took a short 1 minute video of the issue if you are interested.

Noisey Engine Idle



Edited by johnboy1022 on 07-15-19 06:42 PM. Reason for edit: No reason given.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3837
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
07-15-19 08:18 PM - Post#2770788    
    In response to johnboy1022

I agree with bowtie.
Test the fuel pressure with it running.
It could have a broken fuel pressure regulator spring.

The Youtube sounds like it is lacking fuel.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
johnboy1022 
Poster
Posts: 38
johnboy1022
Reg: 08-14-15
08-04-19 03:48 PM - Post#2772408    
    In response to Chevytech

Just following up. I replaced the regulator spring because I had to anyway and it's not the spring. It has a new fuel filter. I realized that it isn't getting fuel for the duration of how long I keep the accelerator pushed in. It's like it only is getting a brief shot of fuel and no more. Also, I cannot hear the pump prime up when starting the truck. I've replaced the pump and bench tested them successfully. I checked the fuse as well and it is fine. Could it be a relay or something not feeding steady current to the fuel pump? The computer maybe?



Edited by johnboy1022 on 08-05-19 09:24 AM. Reason for edit: No reason given.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3837
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
08-05-19 05:50 PM - Post#2772480    
    In response to johnboy1022

Putting a fuel pressure gauge on it would take out the guess work.

If the fuel pump relay is bad the computer should have stored a trouble code 54.

A code 54 happens when the computer does not see power on the circuit from the fuel relay to the fuel pump, when the computer is sending power to the relay to apply the relay.

Have you checked the ECM for codes?

If you have unplugged the fuel relay and turned the key on there could be a false code set by doing this.

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

There will only be power to the fuel pump for a few seconds when you first turn the key to the on position. If you are turning the key on then walking around the vehicle testing for voltage to the fuel pump circuit, there will be no voltage, and should not be power to the pump after a few seconds.

When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/sender. This circuit is independent of the fuel pump relay.

Once the engine has oil pressure the fuel pump should get power even if the relay has failed.

Wire color
A wiring schematic or your truck would make your task much easier. Make sure you use the correct model year because GM changed the wire colors on these circuits somewhere around 1990.
1993 has a gray wire to the fuel pump.

On a 1988 &1989 the fuel pump feed wire is light brown with a white stripe (tracer). On later models this wire is gray.

The power wire to the relay is Orange and comes from a fusible link that gets power from the junction block on the firewall by the relay.

The relay ground wire is black with a white stripe.

The control wire from the computer is Dark Green with a white stripe. It should have power for at least two seconds when you first turn the key to the on position.


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
johnboy1022 
Poster
Posts: 38
johnboy1022
Reg: 08-14-15
10-06-19 02:54 PM - Post#2777193    
    In response to johnboy1022

Just to put a pin in this. I replaced the map sensor and the O2 sensor. The problem is now resolved. Thanks to all for the help. It was very much appreciated.



 
deckeda 
Poster
Posts: 79

Reg: 08-13-18
10-08-19 02:24 PM - Post#2777398    
    In response to johnboy1022

What made you replace those two, and do you know which of the two was bad? Knowing this might help others in the future.

'89 C3500 dually 2WD, 4-sp (SM465)


 
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