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.