sort of stumble at idle

[Toms007]

Well the vacuum gauge here at school is MIA, so I went up to the parts store at lunch and bought one.

Originally I thought I would hook into the power brake booster line, but the hoses that come with the gauge is pretty small, so where would you suggest I "tie" into the system? Directly into the intake manifold?

 

[LT4man]

Do you have a vacuum gauge? Please connect it to intake manifold vacuum.WILL SOMEBODY PUHLEASE SAVE the

Class, please pay attention! This does not refer to me, the teacher, because I am so POOR, I cannot afford to even PAY attention!

Yes, Tom. If you look at the left (driver's) side of the intake manifold, I believe you will see a small metal nipple with a small vacuum hose attached. If you have a plastic "tee", I would tee the vacuum gauge to that nipple.

The power brake booster hose is good for running Sea Foam through the engine. Way too big for our purposes.

SAVE THE

 

[Toms007]

On my way home in a few minutes. I'll change clothes and get the car down and do some checking. First check all electrical connections on and around opti-coil-etc. Then on to check ALL ground points, then I'll double check the vacuum lines for checks/cracks/broken T's & L's etc. Then I'll get a vacuum reading.

 

[LT4man]

Good idea to check all those electrical connections. Only takes one to cause all of your problems. After checking each one, start and listen to your engine. I am sure by now you will know right away if your LT1 is humming & purring.

Vacuum hoses are often overlooked. You have one going to your Cruise Control and you also have one going to your electric air pump tucked in the front bumper in front of the left front tire.

Do not forget the vacuum check valve on the right (passenger) side of the intake manifold. Removing both fuel rail covers will give you lots of access.

SAVE THE

 

[Toms007]

Please connect it to intake manifold vacuum. How much do you have when the engine is first started? When I first started it up I had 14"
How much do you have when it is in closed loop after warming up? Once in Closed loop it went to 15"

Is it steady at all times? At idle it was steady, of course when I revved it it would climb and fall. If it fluctuates, how much does it move? Held at a steady 1500 rpm it would hold 20" and would drop as far down as 11-13" when I would hit the throttle.

How much fuel pressure do you have cold/hot? Fuel pressure is about the same as before the FP change, 41 at idle Did you check the vacuum hose at the fuel pressure regulator? Yes, the hose appears to be just fine.

Does it accelerate in neutral better than when in drive? Today it seemed to rev better in neutral, but put it in gear and she bucks a bit.

Have you checked all your ignition connections? Yes Ignition coil connections. Pulled them cleaned and reseated them. Optispark connections. Again, took apart and cleaned. Ignition wire connections. They all must be clean and tight.

Has there been any improvement since installing fuel pump & knock sensor? Not much if any.

Idled up just fine until it went into closed loop, then it turned on the SES light (43). Just checking the data stream I notice that the left O2 sensor is at 902 mVolts Right O2 61 mVolts (yes you read that right 61). The injector pulses have evened out some but very low in the last streeam 3.4 and 3.1 ms. Spark advance 37* Knock retard 0* Knock sensor 200. Engine rpm 1600

 

[LT4man]

Alrighty! Now we are getting somewhere!

I have to go to a School Board meeting for my parish grammar school. I am on the board and am also chairing the Silent Auction for next year. So I will be out of this loop from 7pm to 10pm.

I do not think you have enough vacuum at idle.

I also am still very suspect of the 41 psi of fuel pressure.

The O2 sensor readings seem to be all over the map!

Did you go over all rubber vacuum hoses really well? Also, do you have electronic A/C controls or manual A/C controls?

Did you check the hose that runs from your right (passenger) side valve cover to the side of the Throttle Body?

Also, have you replaced your PCV valve in the past 2-3 years?

See ya later!

SAVE THE

 

[Toms007]

Alrighty! Now we are getting somewhere!

I have to go to a School Board meeting for my parish grammar school. I am on the board and am also chairing the Silent Auction for next year. So I will be out of this loop from 7pm to 10pm.

I do not think you have enough vacuum at idle.

I also am still very suspect of the 41 psi of fuel pressure.

The O2 sensor readings seem to be all over the map!

Did you go over all rubber vacuum hoses really well? Actually I just came in from looking some more and found some suspect hoses...both of the hoses 5/32" and a 7/32" from the Cruise control module are chalky black, so I have measured them up and will get some new ones for those. There is one 1/4" dia. from near the TB that runs back down toward and under the air handling unit that is chalky as well, it will be replaced. Also, do you have electronic A/C controls or manual A/C controls? I have the Electronic controls.

Did you check the hose that runs from your right (passenger) side valve cover to the side of the Throttle Body? Yes, that one is good as the rubber end on it cracked last year and I replaced it.

Also, have you replaced your PCV valve in the past 2-3 years? Replaced the PCV valve 2 years ago

See ya later!

SAVE THE

I think I need to pull the drivers side valve cover and check the springs & rockers there, because on the last little drive I took, the missing sounds more from this side.

 

[gmjunkie]

Tom,My 94 is pulling 13 lb Cold Open Loop,16 lb Closed Loop warmed to operating temp, at idle with everything turned on!!
I don't think thats the problem!!

I still think there is a power or connection problem somewhere!!
I want you to check some fuses in the panel at the rt end of the dash!!

4th row down #16 5 amp CCM3 and #20 15 amp Oxy Sen
5th row down #21 10 amp ENG 2 ,#22 10 amp INJ 1,#23 10 amp INJ 2
#25 10 amp COIL
6th row down #30 10 amp ENG 1
7th row down #33 5 amp ECM,#35 5 amp CCM1
8th row down #39 5 amp CCM 2
Make sure these fuses are getting a good Connection!!
Check the Main fuses behind the battery too,Make sure that the spades are clean on them!!
Also pull the plugs on the ECM and make sure there isn't any Green pins on the ECM or the plugs!!
Also put a volt ohm meter set on AC on the back of the alternator and see if there is any AC voltage slipping past the diodes while the engine is running,If so How much??:confused
Something is popping this 43,When we find it,We've Found the problem!!

 

[Toms007]

Junkie, thanks, I'll check those things this evening. Thanks for hanging in there with me.

 

[Toms007]

I checked all of those fuses, cleaned the terminals and reinstalled. Replaced the chalky vacuum hoses and then fired it up.

Runs better but still not quite there yet. Don't have time to take it out tonight and drive it, but will do that tomorrow. Runs quite a bit smoother, but still after going into closed loop it set the dreaded 43 code. I have a data stream that I will download and post later.

 

[Toms007]

Sorry, school started this week so I have been a bit inundated.

Here's the latest data stream.

Desired Idle (RPM) 675 675 675 675
Engine RPM (RPM) 1775 1775 1775 1775
Coolant Temp (°F) 192.2 192.2 192.2 192.2
Oil Temp (°F) 155.7 155.7 155.7 155.7
Manifold Air Tmp (°F) 90.9 90.9 90.9 90.9
A/C Pressure (PSI) 75 75 77 77
MAP Sensor (Volts) 0.82 0.8 0.84 0.8
Throttle Sensor (Volts) 0.72 0.7 0.72 0.72
Throttle Angle (%) 3 3 3 3
Battery Voltage (Volts) 13.7 13.7 13.6 13.6
Barometric Press (Volts) 4.33 4.33 4.33 4.33
Left O2 Sensor (mVolts) 950 893 893 897
Right O2 Sensor (mVolts) 206 418 224 79
Block Learn Cell 17 17 17 17
Left Block Learn value 129 129 129 129
Right Block Learn value 129 129 129 129 Left
Integrator value 128 128 128 128
Right Integrator value 138 133 137 134
Left Inj Pulse (mS) 3 3 3 3
Injector Pulse (mS) 3.2 3.1 3.2 3.1
Mass Air Flow (gr/sec) 13 13 13 13
CCP Duty Cycle (%) 0 0 0 0
Idle Air Mtr Pos (steps) 24 24 24 24
Learned Idle Pos (steps) 21 21 21 21
Spark Advance (°) 36 36 37 36
Knock Retard (°) 0 0 0 0
Knock Sensor 182 182 182 182
EGR Duty Cycle (%) 0 0 0 0

The things that seem to stand out I highlighted. The readings are 1/2 second intervals.

 

[LT4man]

Hi ya, Tom!

For you & the other folks who might be following this thread, I would like to point out some things.

The reason I asked Tom to take vacuum gauge readings is NOT because I believe his engine has a vacuum leak of some kind. Since I started in the repair business in 1973, I was taught to ALWAYS hook up a vacuum gauge if I encounter a driveability issue. The vacuum readings tell me what is working correctly and what is not working correctly.

Tom's problem(s) with his LT1, while being puzzling for awhile, are NOT unrepairable.

I believe Tom's engine vacuum is a bit low. While many engines will run with vacuum in the 13-15in. range, that is not to say they are incapable of producing more vacuum.

As an example: My LT4 has between 19-21in. of vacuum at idle. Depends on the temp of the engine & how many accessories are operating. While the LT4 is a higher performance engine than the LT1, that does not mean the vacuum will be necessarily higher. In fact, because of the LT4 camshaft, (higher lift, longer duration) & the higher compression ratio (10.8:1 vs 10.4:1), common experience would dictate the LT4 engine would have a lopey idle & much less vacuum than the LT1. I do not believe this is the case. Every LT1 I have seen has similar vacuum readings to my LT4. Electronic engine controls are the main reason for this.

But, I digress! :bash

Armed with Tom's recordings of his engine vacuum will help me point Tom in the right direction for his correct diagnosis. Already Tom has pinpointed some vacuum hose issues. Junk's advice to check all electrical connections is spot on! I understand Tom's Vette has higher mileage (He keeps driving the thing cross-country! Like me!) than most.

I will be studying Tom's recent numbers he pulled from his scan tool.

Tom, some questions for you: How many miles does the engine have? What mods have been done to your engine? I believe I remember you telling me you have the 1.6:1 rocker assys. Is that the only change to the drivetrain? Are you running a different exhaust system than stock? When were the spark plugs & ignition wires last replaced? Are you running the original Optispark?

Thanks very much, Bro!

SAVE THE

 

[Toms007]

Hi ya, Tom!

For you & the other folks who might be following this thread, I would like to point out some things.

The reason I asked Tom to take vacuum gauge readings is NOT because I believe his engine has a vacuum leak of some kind. Since I started in the repair business in 1973, I was taught to ALWAYS hook up a vacuum gauge if I encounter a driveability issue. The vacuum readings tell me what is working correctly and what is not working correctly.

Tom's problem(s) with his LT1, while being puzzling for awhile, are NOT unrepairable.

I believe Tom's engine vacuum is a bit low. While many engines will run with vacuum in the 13-15in. range, that is not say they are incapable of producing more vacuum.

As an example: My LT4 has between 19-21in. of vacuum at idle. Depends on the temp of the engine & how many accessories are operating. While the LT4 is a higher performance engine than the LT1, that does not mean the vacuum will be necessarily higher. In fact, because of the LT4 camshaft, (higher lift, longer duration) & the higher compression ratio (10.8:1 vs 10.4:1), common experience would dictate the LT4 engine would have a lopey idle & much less vacuum than the LT1. I do not believe this is the case. Every LT1 I have seen has similar vacuum readings to my LT4. Electronic engine controls are the main reason for this.

But, I digress! :bash

Armed with Tom's recordings of his engine vacuum will help me point Tom in the right direction for his correct diagnosis. Already Tom has pinpointed some vacuum hose issues. Junk's advice to check all electrical connections is spot on! I understand Tom's Vette has higher mileage (He keeps driving the thing cross-country! Like me!) than most.

I will be studying Tom's recent numbers he pulled from his scan tool.

Tom, some questions for you: How many miles does the engine have? 118k. What mods have been done to your engine? I believe I remember you telling me you have the 1.6:1 rocker assys. Crane Gold Roller Rockers 1.6:1 Is that the only change to the drivetrain? Yes, well K-N with a cut lid. Are you running a different exhaust system than stock? Corsa When were the spark plugs & ignition wires last replaced? Changed about a year and a half ago 5K back NGK Platinums/OEM wires Are you running the original Optispark? No, I changed it out the same time as the plugs/wires (Genuine GM/Opti and Water pump)

Thanks very much, Bro!

SAVE THE

Questions answered.

 

[Toms007]

LT4Man, as per our phone call, the KS readings were 3800 and 3900 left and right respectively, well within range. I did not have a chance to take it out today but will as soon as I can. I had someone ask if I took those readings with the engine HOT........made me think there might be something to that, as the engine warms up the resistance changes. What do you think, probable? I'm pretty sure it's possible.

 

[LT4man]

Good question!

I see you will be driving it a bit. Best thing for it. I would drive it fast, slow, in between, make plenty of stops, make plenty of starts.....really drive it like you are thinking of buying it!

I would get it totally warmed up & then take the Knock Sensor readings again.

SAVE THE

 

[kcrick]

This thread reads like a murder mystery! I can't wait for the next chapter! My 94 is still in the shop...they're trying to diagnose a stumble as well...I wish it was in the garage here so I could check these things! Although they have the coolest scan tool...

 

[vette079]

Don´t attack me on this one (I´m no tech) but on the scans it shows very different values for the right and left O2 sensor readings.

Are they supposed to be that way?

Spark advance at 36degrees. After the first scan that was posted someone mentioned it was retarding and it showed some 20degrees advance on the scan.

I assume this was at idle?

But again, I´m not trying to be the wise guy here, just looked weird in my eyes and also trying to learn something here.

A very interesting thread I must say (write).

 

[Toms007]

Don´t attack me on this one (I´m no tech) but on the scans it shows very different values for the right and left O2 sensor readings.

Are they supposed to be that way?

Spark advance at 36degrees. After the first scan that was posted someone mentioned it was retarding and it showed some 20degrees advance on the scan.

I assume this was at idle?

But again, I´m not trying to be the wise guy here, just looked weird in my eyes and also trying to learn something here.

A very interesting thread I must say (write).

Yes, the other to scans were at idle, hence the less advanced readings. The last one was at 1775 rpm. Those O2 readings were something that caught my eye as well.

Even though it was showing 20* advance the KS were pulling some of the timing out. I have the KS issue fixed, just need to get the car out and drive it a while to see where I am now, just don't seem to have enough
time after work to get it done though...maybe this weekend.

Thanks to all who post here, I will get this figured out and back on the straight and narrow.

 

[Toms007]

OK, I just got back from a 20 minute outing. She still isn't right. she still wants a "buck" while accelerating and exhibits no power. I had the scan tool hooked up and was monitoring it (as best as I could) while driving it down the highway.

Something is still pulling the timing out when I try to accelerate. Once up to a cruise the engine is running with 40-42* advance and no knock retard, but as soon as I try to accelerate the timing drops to as low as (what I noticed) 20* and knock retard 12*. I have 30 seconds of scan time recorded (and in Excel format) if someone would like to see it and decipher it for possible solutions, that I can email LMK.

Code 43 still in History even though I clear it. so I am guessing this is where my troubles lie. The KS test out OK, so I am leaning toward KS Module (I still have to check it, per FSM).

On the bright side, I may have found my oil leak...actually I think it is Power Steering fluid, before I took it out I checked all the fluids and the PS was low, I put in some Lucas PS stuff and leakage when I got back from the drive was minimal. (Got my fingers crossed that this was it).

 

[Toms007]

Alright, here's what I found:

Checked the resistance of the KS while the engine was still hot virtually the same readings 3800 both right and left (3300-4500 spec'd) So I don't think that is where the problem lies.

Following the FSM diagnostic procedure for code 43 I pulled the "D" connector out of the ECM and then checked the wire to the KS for voltage I got O volts. So the flow chart says No Voltage means 1. faulty KS (I don't think so) 2. Faulty KS module (could be) 3 Faulty ECM (maybe).

Here's a kicker...in the process of removing the ECM from the mount I noticed that the ECM is really hot. Hot enough that it is difficult to hang on to bare handed, and this is after the car has been shut off for 45 minutes.

Also, I can't find where the Knock Module is...anybody here know where it resides?