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Username Post: stumped        (Topic#357666)
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-15-19 06:28 PM - Post#2773272    

Hi there guys and gals, I need help on mt 98 chevy 2500 7.4. I am going to start from the beginning of this project. I need to rebuild the motor so I stroked it to a 489 cc. After finally getting it back in the truck. It ran great for about three hundred miles. I had a hard starting problem for awhile. I decided to look into it. And found number two injector just pooring out fuel and a couple of the ones on the odd bank leaking a little bit. So i get the new harness and fuel rail along with all new delphi injectors. Figured that i would be done with it. Nope after about a couple hundred miles it started to run like poopoo again. I found one of the injectors was stuck open. replaced it and it still ran like poopoo. So i ended up taking it to a shop for them to look at it and the wanted to pull the upper intake off and look at the injectors. I could afford them to have it any longer then they already had had it for four already. they replaced number 2 and 3 plugs for 27.00 in parts. So i take it home and take off the upper intake and find that there wasn't ant injectors leaking. So I replaced the fuel regulator. replaced the number 2 and 3 plugs and started it up and it still don't run right. And while i was waiting for the regulator to come i put the old injectors on the fuel lines to see which injectors was leaking for sure and none of them was leaking. Sorry for a long post just trying to give you the hole story. Thanks in advance for any and all help that you may help with. The motor now has almost a 1000 miles on it. and did a compression test they range from 165 to 182. Thanks Mark



 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2727
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
08-15-19 06:50 PM - Post#2773274    
    In response to 98 vortec 7.4

Does that truck have a distributor?
If it does inspect it closely.
Remove the cap and wiggle the shaft.
The teeth may be worn under the distributor as well making it not fire properly
Welcome to ChevyTalk

Old School GM fan FOREVER


Edited by rockfangd on 08-15-19 06:51 PM. Reason for edit: No reason given.

 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-15-19 08:05 PM - Post#2773283    
    In response to rockfangd

Thanks, yes it does have a dist, but like every thing else its brand new and wires. the only things that aren't new are the block, heads, and upper and lower intake.



 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
08-16-19 04:27 AM - Post#2773295    
    In response to 98 vortec 7.4

The stock injectors are supposedly not a great design, but I've got almost 300K miles on mine.

I would recommend checking your fuel pressure.

99 K3500 RCLB


 
bowtie44s 
Valued Contributor
Posts: 4236
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
08-16-19 07:15 AM - Post#2773300    
    In response to 98 vortec 7.4

Is your check engine light on?

The timing has to be set with a scan tool. If you didn't use a scan tool the timing is off. The Vortec distributor is prone to have the cap screws strip. Check them to make sure they aren't.

As 454cid said, it never hurts to check fuel pressure.

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


 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-16-19 05:15 PM - Post#2773334    
    In response to bowtie44s

okay guys, there was no check engine light on until i moved the dist today. And off course i got the p 1345 code. And i have been checking the fuel pressure. Its at 50 psi. i happen to look at the gauge when it was not running and it jumped up 10 to 15 pounds. So I guess that i need a new furl pressure tester. lol but between both fuel regulators its been 50 psi. I will let you know more after i get a new fuel pressure gauge. To make sure what the fuel pressure is. Thanks Mark



 
bowtie44s 
Valued Contributor
Posts: 4236
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
08-17-19 06:57 AM - Post#2773366    
    In response to 98 vortec 7.4

Someone else will know for sure but I think it should be 60. 10psi low is enough to cause problems.

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


 
CowboyTrukr 
"8th Year" Silver Supporting Member
Posts: 4244
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
08-17-19 08:51 AM - Post#2773373    
    In response to bowtie44s

Yup. 10% low on a TBI’s fine. 10% low on the Vortec is bad. 17% low is horrible.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
454cid 
Valued Contributor
Posts: 3112

Age: 46
Loc: West Michigan
Reg: 02-18-12
08-18-19 07:15 AM - Post#2773470    
    In response to 98 vortec 7.4

50 isn't horrible, but it's a little low. I think mine is only 55ish and it runs fine. The 454 doesn't needs as much pressure as the 350.

99 K3500 RCLB


 
someotherguy 
Senior Moderator
Posts: 28990
someotherguy
Age: 49
Loc: Texas
Reg: 08-01-03
08-18-19 12:07 PM - Post#2773489    
    In response to 454cid

58-62 psi is spec for the Vortec big block. They absolutely will start and run on significantly lower pressure, just will not run well. The individual "real" injectors vs. the small block poppet style do not require full pressure to operate, so you don't generally get the "fuel pressure drops a little, engine won't start" issues the small block suffers.

Richard

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


 
65_Impala 
Very Senior Member
Posts: 4240

Reg: 12-29-02
08-19-19 10:01 AM - Post#2773557    
    In response to 454cid

Per previous posts it seems the regulator on those engines is vacuum referenced so the pressure at idle is lower than the spec. A couple of people troubleshooting and posting results have pretty much proved that's how it works. The spec must be with the key cycled and engine off.

ih-hg to psi is approximately a 0.5 ratio, so 20in-hg of vacuum at idle would cause approximately 10psi less pressure with a vacuum referenced fuel pressure regulator.

This would also be why the pressure went higher with the engine not running.





 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-23-19 08:01 AM - Post#2773873    
    In response to 65_Impala

Okay guys, I got a mew fuel pressure tester. And it reads about 48 psi. I found that the timing was off even though the check engine light wasn't on. I drilled holes in a old cap and stated it up and looked at the spark from the coil and set it to where there was no trailing arc. Runs much better but still have number two and three wet fouling the plugs. I replaced all the injectors and the i found number two leaking again. Not sure what's going on. I think that i am going to put the old injectors back in it and see what happens.



 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-24-19 07:32 PM - Post#2773980    
    In response to 98 vortec 7.4

Okay the newest update. I replaced the number 2 and 3 injectors with two of the used injectors from all this crap started.All so the plugs in those cylinders. Well it is still getting numbers 2 and 3 wet. And now it is only back firing in the intake a little bit. Before when the timing was off it was much worse. I am starting to think that it might be a computer issue. Over feeding those injectors? There is a bit of dampness in the intake. Any new thoughts on this? Thanks Mark



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3825
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
08-27-19 08:54 AM - Post#2774177    
    In response to 98 vortec 7.4

Here are my thoughts.
The fuel pressure spec is specifically for testing with the key on and engine off. The running pressure will be lower because of the fuel pressure regulator operation.

Anytime a fuel injected engine over fuels you should check the temperature sensor.
Coolant sensor testing specs are the same for a big block and are at this link:
https://www.chevytalk.org/fusionbb/showtopic.php?t...

As for wet spark plugs:
You are correct to be suspicious of the injectors. They are a common problem.
This is a sequential fuel injection engine. The injectors are not batch fired. INSPECT THE WIRES TO THE INJECTORS OF THE CYLINDERS THAT HAVE WET PLUGS TO MAKE SURE THE INSULATION ON THE WIRES IS NOT RUBBED THROUGH.

You asked if the computer could over fuel a few cylinders. I think that is a possibility. I have never seen or heard of that happening. I do not have knowledge of the internal PCM operation with the sequential fuel injection circuitry.

Once the spark plugs get soot on them from an over rich mixture the oxygen sensor gets fooled and the system can go full rich even after the problem is fixed but the plugs still have soot on them. Driving the truck at highway speeds does a lot to clean the plugs once the problem is resolved.

Have you check the distributor for wear? The distributor can get so sloppy that it affects the way the engine runs.

Is the valve train and engine perfectly quiet when running with no ticking or knocking?

Are you sure the wetness on the plugs is fuel and not oil or coolant?

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.


 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-28-19 04:22 PM - Post#2774331    
    In response to Chevytech

Thanks chevy tech for your reply. I will look onto the coolant sender. I had to drill and tap the sending unit plug out to a 3/4 pipe fitting and put a reducer in there to put the sending unit in. long story. I was doing some other checking and was checking to make sure that the plug was actully firing. So i put a plug in the hole and put the plug on the spark plug wire and grounded it to the frame. and it made the truck drop about a hundred to a hundred fifty rpms and the truck sounded like it was under a load. When i took it off the frame it went back to normal idle.



 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-28-19 04:31 PM - Post#2774334    
    In response to 98 vortec 7.4

and i also pulled the spark plug wire off while it was running and number 2 didn't change the rpms. I did the same to number 3 and it drop 50 rpms according to the tach. I also did a noid test on the injectors and they are working fine. And i for got to say in the last post that the dist is new and the valve train sounds normal. To reply to chevy tech. Thanks for all the help on this problem. I hope i find it soon. mark



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3825
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
08-28-19 06:47 PM - Post#2774347    
    In response to 98 vortec 7.4

You're welcome.

If pulling the number 2 plug wire did not change the RPMs then you need to find out why.

Here are some possibilities:
No or low compression on that cylinder.
The firing order is mixed up – double and triple check the plug wire order.
You could swap the spark plug with another cylinder to see if the plug is bad and the problem moves.

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.


 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-28-19 09:15 PM - Post#2774364    
    In response to Chevytech

Yes i know that is what i am trying to do. I have double and tripel checked the firing order. I am thinking that maybe a vacuum leak? or maybe a bad ground? I am at a loss for things that it could be



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3825
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
08-29-19 08:01 AM - Post#2774391    
    In response to 98 vortec 7.4

The #2 spark plug is getting wet. If the wetness is fuel then over fuel is more of a concern then a vacuum leak. With port fuel injection the fuel is squirted right into the port so vacuum leaks biggest symptom is and idle speed that is to fast.

Make sure there is spark getting to the #2 spark plug.

You should check the inside of the distributor cap for carbon tracks between the spark plug wire terminals. Make sure you look at #2.

Make sure the #2 cylinder has compression.


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.


 
98 vortec 7.4 
Poster
Posts: 16

Age: 57
Loc: AZ
Reg: 12-13-18
08-29-19 11:24 PM - Post#2774453    
    In response to Chevytech

Yes i have done that. It has 165 compression. New dist, cap rotor wires. the whole nine yards. Since i had the pleunm off testing stuff i decided to pull the intake off and check the gasket. I think that the lower part of the intake gasket on number 2 doenst look like it was sealing well. So i will know more tomorrow when i get it back together.



 
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