Rough Idle - problem solved

[Kowalski]

Dear community,

I just bought a '99 Tahoe 5.7 already with this issue - rough idling, smell of unburnt gas. The previous owner said it is the old injection system according his garage so I decided to change it to the new multi port design with no effect. Initially, I did not want to throw parts at it, but now I have started already.

What I already did:

- compression test (good on all cylinders 10,5 -12,5 bar) with 240.000 km on the clock (most likely)
- new mfi injection system

Now, I want to change the distributor, wires and spark plugs which look really old. For that I need to find TDC and although I removed all spark plugs I can't crank over the engine manually with a 16 mm wrench on the pulley - of course clockwise. What do I do wrong? Do I need to remove the belt in order to reduce friction?

I know the symptom can have numerous causes (fuel pressure, sensors, vacuum leak, etc.). I do not have any codes when connecting it to a (cheap) OBD-reader plus the "check engine"-light is off.

Which advice could you give me on
a) cranking the engine over (see above) and
b) other causes for rough idling and which sequence of testing?


Looking forward of hearing from you.

Kind regards
Falco

 

[Big Mama]

Welcome to the forum from Virginia. I’m not much help on this but more knowledgeable folks will join in.

 

[Kowalski]

Hi Steven,

no problem. Nice cars (Audi TT and Yukon Denali)!

Best whishes
Falco

 

[exp500]

Greetings Kowalski ! Looks like you are stuck with either a 2 man job or a remote starter switch to bump engine to compression stroke. Finger in #1 cylinder, watch balancer mark. ( unless you can see compression guage from key turn position). Sometimes a wrench on alternator works too.
You must set up your scanner to read cam position offset which correlates to P1345 if you don't get distributor in perfect. Which App are you using?

 

[YukonGTmaster]

Dear community,

I just bought a '99 Tahoe 5.7 already with this issue - rough idling, smell of unburnt gas. The previous owner said it is the old injection system according his garage so I decided to change it to the new multi port design with no effect. Initially, I did not want to throw parts at it, but now I have started already.

What I already did:

- compression test (good on all cylinders 10,5 -12,5 bar) with 240.000 km on the clock (most likely)
- new mfi injection system

Now, I want to change the distributor, wires and spark plugs which look really old. For that I need to find TDC and although I removed all spark plugs I can't crank over the engine manually with a 16 mm wrench on the pulley - of course clockwise. What do I do wrong? Do I need to remove the belt in order to reduce friction?

I know the symptom can have numerous causes (fuel pressure, sensors, vacuum leak, etc.). I do not have any codes when connecting it to a (cheap) OBD-reader plus the "check engine"-light is off.

Which advice could you give me on
a) cranking the engine over (see above) and
b) other causes for rough idling and which sequence of testing?


Looking forward of hearing from you.

Kind regards
Falco[/

Yes! Remove the serpentine belt before turning the crank with a socket and ratchet.

 

[exp500]

You should also do fuel pressure tests at fuel rail. I prefer a long hose on guage to see it while driving.

 

[east302]

Did you mark the distributor base position and rotor location of the old distributor? If so, and you haven’t turned the crank, just position the new one in the same position and drop it in. The rotor will turn clockwise as it is seated, so put the new distributor rotor in the same location as the old one was when it came up. When it seats, it should then be in the same location as the old one was before it was removed.

Rotate oil pump shaft slightly to align during seating.

Here’s the long version of that:

 

[willxfs]

All good advice above. I crank my engine over by hand using the bolt in the center of the harmonic balancer. Think I have to remove the fan and clutch first. Cant quite remember. I like to use the method described in the link below to set the distributor. Good luck.

http://www.gmtruckcentral.com/articles/distributor.html

 

[Kowalski]

Dear all,

thanks a lot for these valuable pieces of information. This is highly appreciated.

I was able to crank the engine manually by using an extension bar for my ratchet. I am pretty sure I cranked it over to TDC of cylinder #1. My old rotor pointed then to #1 cylinder (not to #8).
Unfortunately, I didn´t mark anything because I only read your advice, especially the one of "east 302", only afterwards.

Please take a look at the pictures:

1) Did I really find #1 TDC? Isn't this a strange mark on the pulley? I carefully inserted a screwdriver into the bore of my spark plug and found that the piston is almost at one level of my spark plug hole.

2) Is the newly installed distributor pointing into the correct position (#1 TDC)? I think it is a little bit too far off its intended position (clockwise).


I tried to start my engine but now, it won't crank easily. It feels like as if the battery is low. So I charged it again (fully charged) but same effect. It feels as if the is too much compression and it only started for a moment still running rough, stalls and then didn't start again. Is it possible that I brought in another fault with my new distributor? Is it possible that the converter is clogged because too much unburnt fuel is now inside?

I wondered why the compression test for cylinder #5 was so high (17 bar)? Was too much fuel inside the cylinder at the time of testing?


I am really looking forward for some advice again. The Tahoe here is quite rare and so it is hard to find a good garage.


Best whishes
Falco

 

[exp500]

Kowalski- Please reply with the app you are using for trouble codes.(post 4 above) Sounds like you met the Dreaded p-1345. Usually requires the Additional GM specific codes (or PIDs) .Result is the same, must move distributor slightly, As computer sets actual timing. Setting is 0 degrees+-1. above 1000 RPM.

 

[YukonGTmaster]

Dear all,

thanks a lot for these valuable pieces of information. This is highly appreciated.

I was able to crank the engine manually by using an extension bar for my ratchet. I am pretty sure I cranked it over to TDC of cylinder #1. My old rotor pointed then to #1 cylinder (not to #8).
Unfortunately, I didn´t mark anything because I only read your advice, especially the one of "east 302", only afterwards.

Please take a look at the pictures:

1) Did I really find #1 TDC? Isn't this a strange mark on the pulley? I carefully inserted a screwdriver into the bore of my spark plug and found that the piston is almost at one level of my spark plug hole.

2) Is the newly installed distributor pointing into the correct position (#1 TDC)? I think it is a little bit too far off its intended position (clockwise).


I tried to start my engine but now, it won't crank easily. It feels like as if the battery is low. So I charged it again (fully charged) but same effect. It feels as if the is too much compression and it only started for a moment still running rough, stalls and then didn't start again. Is it possible that I brought in another fault with my new distributor? Is it possible that the converter is clogged because too much unburnt fuel is now inside?

I wondered why the compression test for cylinder #5 was so high (17 bar)? Was too much fuel inside the cylinder at the time of testing?


I am really looking forward for some advice again. The Tahoe here is quite rare and so it is hard to find a good garage.


Best whishes
Falco

View attachment 279180 View attachment 279181

That mark does not look like the TDC groove on your harmonic balancer. It should be a defined machined groove perpendicular to the balancer wheel. That mark you have it aligned to, looks very suspect. Note the mark on the attached picture. I would pull your belt off and rotate the balancer clockwise 360 degrees and look with a bright light.

 

[BG1988]

Yes! Remove the serpentine belt before turning the crank with a socket and ratchet.

you can manually crank it by pressing the starter relay

 

[exp500]

BG1988- Please post a pic of said relay on this vintage! Sauce or it doesn't exist!

 

[BG1988]

BG1988- Please post a pic of said relay on this vintage! Sauce or it doesn't exist!

the old mechanics trick was to squeeze the relay for the starter to manually crank it


why not use the key? and pull the fuel pump fuse

 

[willxfs]

Kowalski,

It really sounds like you set your distributor with No. 1 cylinder at TDC on the exhaust stroke not the compression stroke. To set the timing correctly, No. 1 cylinder need to be at TDC on the compression stroke. The easiest way to identify if you are on the compression stroke is to have someone put their finger over the spark plug hole of No. 1 cylinder while you turn the crank with your ratchet. As the No. 1 cylinder is coming up on the compression stroke, the pressure will try to push your friends finger off the hole. It will be very noticeable. You will also notice that the machined groove on the balancer will line up with the V shaped marker on the timing cover. Good luck.

 

[Kowalski]

I used a wrong mark on my pulley - you were all right. So yesterday, I found the correct mark and was able to install my new distributor correctly.

But still, it is idling rough with strong smell of unburnt gas. I then disconnected the mass airflow sensor and it then ran smooth! Unfortunately, it idles at appr. 1400 rpm and I do not have any brake assistance. Maybe I forgot to connect a hose so that I do not have sufficient vacuum?

1)
I need an OBD-reader. My garage doesn't have a proper computer for this model. Which affordable OBD reader do you recommend for this model?

2)
Which sensors might be malfunctioning? How can I test whether it is a defective MAF-sensor or something else?

 

[exp500]

Kowalski- BAFX has a decent bluetooth, It will do alot but not any 2 way EG-Commanded such as ABS or heater. transmission/ Tcase/ 4x4/ . The VXDIAG clones are good, you may need to find a retailer in your country, Here are a couple examples-
https://www.chinacardiags.com/whole...or-gm-saab-opel-suzuki-isuzu-holden-1011.html
https://www.chinacardiags.com/whole...-gds2-diagnostic-tool-wifi-version-17410.html
https://bafxpro.com/products/obdreader

As far as how its running- Follow your Brake booster hose back to the intake, you will probably find a leak there. Recommend to test for vacuum leaks with Brake Kleen or similar, small dribbles along suspect area. If it is leaking rpm will change.
Likely that you still have a check engine light on. See above posts.
Keep Updating us!

 

[YukonGTmaster]

I used a wrong mark on my pulley - you were all right. So yesterday, I found the correct mark and was able to install my new distributor correctly.

But still, it is idling rough with strong smell of unburnt gas. I then disconnected the mass airflow sensor and it then ran smooth! Unfortunately, it idles at appr. 1400 rpm and I do not have any brake assistance. Maybe I forgot to connect a hose so that I do not have sufficient vacuum?

1)
I need an OBD-reader. My garage doesn't have a proper computer for this model. Which affordable OBD reader do you recommend for this model?

2)
Which sensors might be malfunctioning? How can I test whether it is a defective MAF-sensor or something else?

I went with OBDLINK MX+ bluetooth scanner. I downloaded DashCommand off the App Store, and did the in App GM Extended Parameters for $9.99, which allowed me to read Cam Retard Offset to dial in the distributor.

 

[Kowalski]

Dear all,

thank you very much for your valuable information! With your help I was able to fix the problem:

It costs 12 USD (10 €): A spray can of mass airflow sensor cleaner and 10 minutes!!! It was that simple! Engine ran smooth of cleaning the MAF sensor.

Unfortunately, I did the cheap fix after installing a new MFI injection spider and a whole new distributor, wires and spark plugs. Ok, It was not a waste of money because the distributor was old was the old plastic style model and from I have heard it was also not too bad to convert to the new style MFI injection. So all in all not a waste of money.

I did also a bad mistake when I reassembled the upper intake - I forgot to connect the main vaccuum hose to the upper manifold. Now it idles at 600 rpm including brake assistance again. Thanks for your hint, exp500.

I also ordered a bafx-OBDII reader and will then use the DashCommadn-app like YukonGTmaster recommends or the Torque Pro-app in order to set the right timing of my new distributor (idling could still be a little smoother I guess).
Secondly, I ordered a new MAF sensor but not the original Delphi but a Walker model. I know, maybe I should have invested these 60 $ more to get an OEM part, but after spending 1000 USD for parts which were not essential to get it running I was a litlle greedy.

I am really happy now! Next week I need to get a new "Warrant of Fitness" and I hope that the inspector will not find any other defects.


So again, thanks to all of you!


Best whishes
Falco

 

[exp500]

Kowalski- Glad you were successful! Good Job, many suffer long hours with similar. What a Test of your abilities. Welcome to the boards And continue posting.