Gain extra benefits by becoming a Supporting Member Click here find out how!

Classic Performance Products Nu-Relics Power Windows
American Auto Wire Hellwig Products IncPerformance Rod & Custom
Danchuk Catalog



Username Post: Spark plug gap - new fuel injectors        (Topic#365574)
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25483
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
06-21-21 01:06 PM - Post#2821911    

My "other" truck had a #6 FI failure (2000 5.2L). I could not find the same replacement injectors. So I found similar injectors to use. Stock FI are one hole. The new ones are 4 hole. The new injectors are powered down to 19 lbs/hour(from 24 lbs/hour). Originals are 16 lbs/hour. The first updated set ran for 5 years. The new set give code P0172 right away. The ECM compensates RPMs after a few seconds. Idle is smooth and steady. The problem is still P0172 set within a few miles. I'm starting to wonder if two things are setting the code. First, the cooler thermostat instead of 195F. Second, the stock spark plug gap for a one hole FI is 0.040. Would changing the spark plug gap help burn fuel better? Or should I make more modifications to get more into the engine? The truck also has two new OEM O2 sensors, cat front/rear.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


Edited by gchemist on 06-22-21 03:10 AM. Reason for edit: change from PSI to lbs/hr

 


Rick_L 
Member #409
Posts: 27879
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
06-21-21 03:30 PM - Post#2821916    
    In response to gchemist

You're getting the code because the engine is running too rich. This is because your ecm isn't programmed for your apparently bigger injectors, and they are enough too big that the ecm won't pull enough fuel out.

So what you need to do is get the correct injectors, or get the ecm programmed with the correct injector data.

What is this 24 psi/19 psi/16 psi business? Those sound more like injector flow rate than fuel pressure. Which comes back to the injector data.



 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25483
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
06-22-21 03:08 AM - Post#2821925    
    In response to Rick_L


I was thinking of equipment in semiconductors while typing. I'll go back and fix it. The rate should be lbs/hour.

The four hole injector is a suitable replacement. All it needs is a correct EV connector. New connectors were installed along with new injectors. Even with the code, I can tell MPG is up. Power is nice and smooth. I think it's the start up idle RPM swings that set the code. Once the ECM makes adjustments, it runs smoothly.

It ran a set for over 30,000 miles without a glitch. The new set, from a different manufacturer, seem to be slightly different. I'll take OHM readings between the old and new sets. I'm curious if a spark plug gap change can compensate a little for added fuel. A 3 lbs/hr change.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


Edited by gchemist on 06-22-21 03:12 AM. Reason for edit: No reason given.

 
Rick_L 
Member #409
Posts: 27879
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
06-22-21 06:46 AM - Post#2821933    
    In response to gchemist

Thermostats and spark plug gap will not affect your problem.



 
IgnitionMan 
Valued Contributor
Posts: 3897

Reg: 04-15-05
06-22-21 08:43 AM - Post#2821940    
    In response to gchemist

If you are really into both ignition system and other system problems, by all means, open that spark plug gap up over .045, that'll make it just plain problem prone



 
someotherguy 
Senior Moderator
Posts: 29435
someotherguy
Loc: Texas
Reg: 08-01-03
06-22-21 11:38 AM - Post#2821950    
    In response to Rick_L

  • Rick_L Said:
Thermostats and spark plug gap will not affect your problem.


Hey Rick, are you 100% sure on the thermostat? When I saw him mention he's not running the stock temp thermostat that sounds like a red flag to me. Without programming to compensate for a colder thermostat, he may be causing fuel mixture issues.

G, any reason you're not running the 195F?

(I do fully realize a colder thermostat does not -necessarily- result in colder operating temperature)

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
65_Impala 
Very Senior Member
Posts: 4761

Reg: 12-29-02
06-23-21 08:53 AM - Post#2822000    
    In response to gchemist

How did you "power down" the injectors from 24lbs/hr to 19lbs/hr?

What is the thermostat temperature? Not that it likely matters, the engine will most likely go closed loop somewhere around 100-120*F.

0.040" to 0.045" is a good range for the plug gap. If it's coil on plug it could fire 0.060" gap when the plugs are new, but it won't take long to start running rougher and then getting misfires. And, the bigger gap won't change the fuel mixture anyways.



 
IgnitionMan 
Valued Contributor
Posts: 3897

Reg: 04-15-05
06-23-21 08:58 AM - Post#2822001    
    In response to someotherguy

"G, any reason you're not running the 195F?"

LOTS of people disregard what should be, and blindly follow top tun4ers and dyno heroes, drop engine temps to drag race levels, and generally make issues not a problem, into giant ones.

Taking an aluminum head engine and dropping the coolant temp from 195 deg/F. down to lower, do not realize, nor have they heard that what that does is lower the combustion chamber operating temp, killing the efficiency from too cold a chamber temp, and too fast a bleed off temperature through the aluminum heads.

Spark plug gaps are another one, maximum would be .045, others insist on murdering ignition components by giant spark plug gaps, and then say the ignition system failed "For No Apparent Reason".

someotherguy, good catch on the engine temps.



 
65_Impala 
Very Senior Member
Posts: 4761

Reg: 12-29-02
06-24-21 12:37 PM - Post#2822051    
    In response to gchemist

I'm assuming you saying truck and 5.2L you might mean a 5.3L LS engine? If it is an LS, the LS engines will run just fine with a 180* or higher rated thermostat, especially in the heat you'll see in Texas. You won't see any drivability or mileage issues. It's been well proven by many people doing it that even a 160* thermostat doesn't negatively affect the operation of an LS engine in summer type weather. It's only negative effect might be on the long term engine durability. So, I'm very doubtful any thermostat you stick in it would cause issues. Still, I'm curious what temperature of thermostat you're using.

It's possible you could use an adjustable fuel pressure regulator and dial down the fuel pressure at the rails which would compensate for the larger injectors. It might have some transition fueling issues due to different injector characteristics but then it might be OK. Something like about 10psi down would do it. If you had a scanner you could watch the fuel trims and adjust until they move back closer to zero.





 
IgnitionMan 
Valued Contributor
Posts: 3897

Reg: 04-15-05
06-25-21 06:43 AM - Post#2822077    
    In response to IgnitionMan

The best way to "handle" the larger injectors is to not change fuel pressures all over the place, but, to alter the injector "duty cycle" in the computer, change the actual time the nozzle squirts, to a time that works to give correct fuel to air delivery.

Changing a pressure, while not changing a duration isn't really a viable solution, it is like necking down a water hose to your garden, dribbles don't work.

Also, running an engine at a lower water temp than designed is not the way to go, as the temperature is sensed and added to the overall fuel and ignition curves (injector duty cycle), and too cold makes for erratic settings.

If you are drag racing the vehicle, then, yes, you can jack the temp all over the place, and might, might gain some minute fraction of a second in a drag race, but, not for street use.



 
65_Impala 
Very Senior Member
Posts: 4761

Reg: 12-29-02
06-25-21 08:38 AM - Post#2822078    
    In response to IgnitionMan

You 100% can change the injector flow rate by changing the pressure. People who actually do custom EFI installs and modifications do it all the time and understand how it works. The stock 58psi vs using 48psi or even using 43psi is within the normal operating range of the injectors. That pressure change is not going to change the injector spray pattern.

On LS engines, the fuel rail pressure is held constant at around 58psi. This means the injector flow rate is varied with the amount of manifold vacuum since the flow rate is caused by the pressure differential across the injector. Effectively, the manifold vacuum causes the equivalent of about a 10PSI change in fuel pressure.

No LS computer will be adding extra fuel due to the cooler engine temperature from running a 160*F or 180*F thermostat. It will be in closed loop, full operating temperature mode, by about 100*F. Possibly even sooner. The newer the factory injection system, the faster it goes into closed loop mode. The new stuff goes into closed loop stoichiometric fueling within seconds of starting the engine, not matter how cold the engine is. The old wives tale about how a cooler thermostat messed up the computer and causes the engine to run rich is simply not true about any late 80's or newer GM EFI system.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17648
grumpyvette
Age: 73
Loc: FLORIDA USA
Reg: 03-16-01
06-26-21 10:11 AM - Post#2822130    
    In response to 65_Impala

If your trying to isolate and test and get the engine tune correct, on any efi system,
Id suggest you leave the fuel pressure alone if its at least 40 psi and does not exceed about 58 psi,
and if the fuel pressures consistent, and set the spark plug gap at .043-.045 max and keep th engine coolant temps as consistent and near about 180F-190F as you can get them,
the fewer variable your forced to deal with the better, make the changes in INJECTOR PULSE DURATION and ignition advance curves
to vary the fuel/air ratios and cylinder pressure
to avoid detonation and tuning issues
always start by verifying what your dealing with in temps fuel pressure and sensor function, pull trouble codes and read and tuning instructions, get a shop manual and verify sensor functions and electrical connections electrical grounds, ignition firing orders, do a compression test and verify the valve lash, set the valves if that's required, and make sure your not dealing with partially clogged catalytic converter carefully, verify what your dealing with, don,t guess, verify.
I can assure you that most problems are related to guessing or defective sensors, or assuming somethings working, that you fail to verify, like the ohms resistance in ignition wire or the firing order or verifying TDC, vs the damper/timing tabs
having a set of multi meter/timing light, compression gauge, vacuum and fuel pressure gauges and a shop manual is critical.

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 06-26-21 10:16 AM. Reason for edit: No reason given.

 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25483
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
06-27-21 06:02 AM - Post#2822162    
    In response to grumpyvette

Sorry, I'm replying late. I had to go out of town for a family emergency. I'll read through information and add information. The block is not a 5.3 LS. It's a 5.2 Magnum. Single coil and spark wires. New rotor and cap wires were installed. The OEM fuel pump has 181000+ miles. I'll check fuel pressure. OEM voltage drops 24 lb injectors to 19 based on information I've read. I can gap plugs to 0.045 and give them a try. It's Austin, a 195 around here is bad in traffic. A 180 runs temps at 190 or so in slow and heavy traffic. The mechanical fan is also swapped. The stock 5 blade metal is upgraded too. It has a 10 blade plastic fan. When it's engaged, it pulls a lot more air. Even unlocked, you can hear it pull air through the new radiator.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
Rick_L 
Member #409
Posts: 27879
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
06-27-21 07:32 AM - Post#2822169    
    In response to gchemist

Voltage is not modified to change the amount of fuel through the injector. The practical way to do that is to lower the fuel pressure. The injector is like a switch - to flow more fuel you leave it on longer, or increase the pressure.

As I said earlier, you just need to get the right injectors and run the stock fuel pressure because that's what the ecm is programmed for.



 
IgnitionMan 
Valued Contributor
Posts: 3897

Reg: 04-15-05
06-27-21 07:54 PM - Post#2822215    
    In response to IgnitionMan

Just for clarity, the longer, or shorter time the injector stays open to deliver fuel is called the "duty cycle", increase it, richer, decrease, leaner.

Fuel pressures are critical in modern EFI systems, they don't like severe fuel pressure changes, that is what the duty cycle is for.





 
65_Impala 
Very Senior Member
Posts: 4761

Reg: 12-29-02
06-29-21 04:50 PM - Post#2822331    
    In response to gchemist

Well, your thermostat and running temps aren't causing the issue. Neither is your plug gap.

There are 3 ways you can go to fix it.

Get the correct injectors.

Dial down the fuel pressure until the flow rate of the injectors are within the self tuning adjustment range the computer can compensate for. If previous injectors that are supposed to be the same worked then it ~should~ be close to working with these injectors.

Find a tuner to program the new injector data into the PCM. You will need the new injector data. If you don't have the data, then you need to know the stock injector application so the tuner can pull the injector data from a stock bin that uses those injectors.

The injector opening speed depends on the voltage and that is some of the data you need. Lower voltage and slower opening does cause less flow.




 
Rick_L 
Member #409
Posts: 27879
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
06-29-21 06:31 PM - Post#2822336    
    In response to 65_Impala

  • Quote:
Lower voltage and slower opening does cause less flow.



Indeed it does, and that's part of the data that the ecm needs. But that's not how the fuel flow is primarily controlled. It is a correction.



 
65_Impala 
Very Senior Member
Posts: 4761

Reg: 12-29-02
06-29-21 07:03 PM - Post#2822341    
    In response to Rick_L

Yes, it is a correction because it changes the flow for a certain PWM duty cycle, which means the PCM adds a on-time if the voltage drops. The data helps with starting and some of the transient fueling response.



 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25483
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-04-21 07:04 AM - Post#2822580    
    In response to 65_Impala

Ok, I'm back. It will take a few more days before I can get to the truck. Hopefully on Thur. I'll open up the gap to 0.043. I'll run it a few days. So far, after the ECM adjusts the idle, engine RPMs are smooth. I can check the injector pulse with my power probe IV. A friend has the same truck. I can compare pulse widths to his stock injectors.
Thanks for all the comments and info so far. I'm learning as I go on this truck.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25483
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-07-21 01:57 PM - Post#2822816    
    In response to gchemist

Update: Never trust a city slicker to gap spark plugs! A helper had a few out of gap too small. I reset them all equally to 0.043. The number 6 injector failed a few weeks after a tune up. Well, today, the number 6 plug had two crush washers. :mad : I didn't realize the old crush washer was down the plug hole. Realizing others could have been stuck too, I go back to pull all the plugs out again. No other stuck crush washers were found. I checked for broken or loose vacuum lines. I add zip ties to a few to ensure no loss of vacuum.
The ODBII codes were cleared. I went on a 10 mile test drive. The ECM adjusted idle as it has been doing. The CEL stayed off. The fuel O2 system closed. I'll have to drive it a few days for further testing. Idle is good after it warms up. The plugs still looked new even after a few hundred miles. I'll follow up after a few test miles.
Thanks for all the help and info!

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


Edited by gchemist on 07-07-21 01:59 PM. Reason for edit: No reason given.

 
1983G20Van 
Super Senior Member
Posts: 3887

Loc: Bedford, Texas, USA
Reg: 11-13-02
07-09-21 09:31 AM - Post#2822918    
    In response to gchemist

Cooler thermostat is not going to hurt a thing on that Mopar or a Chevy for that matter.

Before anyone tuned the Mopar ECMs we used a split second map adjuster on them. I had one on my 06 Ram 5.7L and my 03 Dakota 4.7L and my brothers 98 Dakota R/T. We would use software like OBD Link and datalog fuel trims and then adjust the fuel map. I have tuned big cams, head work, headers and bigger injectors with the device.

https://splitsec.com/product/psc1-003-prog rammable...

My 2003 4.7 Dakota had ported heads, Crane 218/224 cams with solid lash adjusters, headers, exhaust, a 2008 intake manifold and larger 2008 injectors. After spending an evening driving around with my brother behind the wheel and me behind the laptop had it running flawlessly.

Split Second made a device that is called a cam tuner as well. It merely adjusts the idle and off-idle fueling and uses a caveman style adjustable knob to increase or reduce fueling. Might be able to find one used.

When Superchips came out for the 4.7L, I flashed the PCM with Superchips to get better timing maps and less torque management but kept the PSC1.

https://youtu.be/LutcPUvgcJk



1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 


Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

700 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.411 seconds.   Total Queries: 16   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 09:23 PM
Top