96 Lumina Hesitation during acceleration

[tcopes]

I have a 96 Lumina 3.1L. This car idles fine but has a bad hesitation during acceleration. When I start from a stop it accelerates initially then bogs down and if I am moving it will also bog down or hesitate while I try to accelerate. When I press the accelerator down to the floor then it will drop a gear, RPM;s come up and it takes off. If I let off the gas a bit it shifts up and loss of power or hesitation is very obvious. It won't maintain a speed of 50 mph without shifting into 3rd but has no problem maintaining 60 when the RPM's are over 2000.
I have put new AC Delco plugs gapped to specs and new premium wires on and they made a huge difference in performance but have not solved the hesitation problem. Checked coil packs and they are within spec, TPS has a smooth resistance curve through its range. No codes are being thrown and it does not appear to be misfiring. Fuel filter has been changed. MAF was cleaned. All with no change in performance. Something is causing a lean fuel condition but don't know where to look. I've heard of the PCM causing these problems in the earlier Luminas, is it a possible source of my trouble here.
Thanks in advance for your replies
Todd

[Schrade]

Check fuel pressure, static motor off, idle with vacuum off of FPR, idle with vacuum ON FPR, and pedal down (guage taped to windshield).

Sounds like the FPR is NOT responding to vacuum change. FP tests should reveal this.

Any vacuum leaks? Any loping when warm idle?

[tcopes]

It idles perfectly, can sit in park and rev the engine up no problems. Do not believe it is a vacuum leak or fuel pump. When I put the peddle down the rpm's jump to 3500 and into the 4000 range and lots of gas then. Will still check out.

This vehicle has a really bad lifter tick. Is it possible that this is affecting the operation of the knock sensor?

Thanks
Todd

[Schrade]

Originally Posted by tcopes

It idles perfectly, can sit in park and rev the engine up no problems. Do not believe it is a vacuum leak or fuel pump. When I put the peddle down the rpm's jump to 3500 and into the 4000 range and lots of gas then. Will still check out.

This vehicle has a really bad lifter tick. Is it possible that this is affecting the operation of the knock sensor?

Thanks
Todd

Yes, it's possible, except if the KS picks up a knock, and retards the timing for TOO long, it throws a code for timing retarded for longer than X seconds/minutes.

Got KS code?

Probably oughtta' do the other tests then...

[Bearwulf]

When was the last time you ran a good high quality fuel sys. cleaner thru it? The Lucas is one of the best on the market. If it has been quite a while, it may take 2 app's.

[richtazz]

Your Lumina came with platinum/iridium plugs, so if you re-gapped them, you may have messed them up. Just cleaning the MAF will do no good if the MAF is shot, so try unplugging the MAF (this should cause the CEL to illuminate which is normal), allow the idle to stabilize, and then drive it with it unplugged to see if it runs better. If it does, your MAF is bad. You may also have a TCC solenoid locking up too early that would cause your symptoms. That's why it's ok in third gear, but not in overdrive.

[tcopes]

After banging my head with this trouble I finally took it in to the garage and had the trouble diagnosed. Their finding was that the knock sensor was advancing the timing to 20 degrees from 7.5 degrees, likely due to the bad lifter. They also found that there was coolant seeping into the intake which I also suspected. They quoted me aprox $1500 to replace the lifters and a few other things while they had the engine apart. The car is not worth fixing for this price but I may attempt to do it myself for $700 or $800 worth of parts.

I have put fuel cleaner through it and also products designed to help fix the lifter problem but nothing improved the situation.

Felpro has designed a gasket that is suppose to fix the leaky intake problem on these GM cars for good. The garage quoted me $194 for this gasket kit which is a bargain if I never have to tear the engine apart again. This garage that I went to was very good and thorough and explained everything to me at my level. It cost me $128 to get the car diagnosed but was well worth the money. They didn't try to throw parts at the car and I got the answers that I went there for. I wanted to make sure that I concluded this thread as I hate searching through forums only to see problems but nobody takes the time to post their solutions or findings. Mine wasn't a cheap fix but at least I know what I have to do to fix it. Thanks to all that replied and good luck to all.

Todd

[manicmechanix]

Originally Posted by tcopes

After banging my head with this trouble I finally took it in to the garage and had the trouble diagnosed. Their finding was that the knock sensor was advancing the timing to 20 degrees from 7.5 degrees, likely due to the bad lifter. They also found that there was coolant seeping into the intake which I also suspected. They quoted me aprox $1500 to replace the lifters and a few other things while they had the engine apart. The car is not worth fixing for this price but I may attempt to do it myself for $700 or $800 worth of parts.

I have put fuel cleaner through it and also products designed to help fix the lifter problem but nothing improved the situation.

Felpro has designed a gasket that is suppose to fix the leaky intake problem on these GM cars for good. The garage quoted me $194 for this gasket kit which is a bargain if I never have to tear the engine apart again. This garage that I went to was very good and thorough and explained everything to me at my level. It cost me $128 to get the car diagnosed but was well worth the money. They didn't try to throw parts at the car and I got the answers that I went there for. I wanted to make sure that I concluded this thread as I hate searching through forums only to see problems but nobody takes the time to post their solutions or findings. Mine wasn't a cheap fix but at least I know what I have to do to fix it. Thanks to all that replied and good luck to all.

Todd

Well if you have to change the intake manifold gasket you will have it torn down to replace the lifter. I can't say if the KS is retarding the timing because of the lifter clacking, but assuming the shop scanned your real-time ignition advance and verified it, then it seems plausible. Anyway, you can get the improved gaskets for about $90 at any auto parts store, $67 at Rockauto online, and I heard that the Doorman kit s the same thing and includes the new bolts for around $60.

[manicmechanix]

Originally Posted by cbec1999

Yes, it's possible, except if the KS picks up a knock, and retards the timing for TOO long, it throws a code for timing retarded for longer than X seconds/minutes.

Got KS code?

Probably oughtta' do the other tests then...

This is why I wouldn't be so sure it's the KS if it would throw a code and he doesn't have one. The FP and FPR would be a good thing to check, although usually a bad FPR cause hard starting I think. In my experience, it's best to take a GM car to a good GM dealer for diagnosis. It cost no more for diagnosisthere, and they usually have an engine mech. with a lot of experience and resources for diagnosing GM drivability problems. Maybe if he unplugged the KS it reverts to retard, so if he has the same problem or no change then it is the KS?

[tcopes]

The guy that runs this shop is a certified GM mechanic, that is why I took it there. The mechanic explained to me that in the earlier years that the tolerances weren't very good for some stuff and it quite possibly wouldn't through a code. Now that I am tearing the top end off the car the lifters are on the list. The only problem is I'm not 100% sure it is a lifter, I have never heard a lifter this bad. Possible wrist pin. I will check out my parts supplier for prices, obviously their prices are inflated.

Todd

[tcopes]

Well I have redone the intake gasket and replaced the lifters (took me about 8 hrs and not really hard) but I still have the knock. I am guessing piston slap. Hesitation trouble still there. I purchased a new knock sensor and tied it to the metal lines on the air conditioner compressor as this was the only place I could ground it within reach of the sensor wire. The car has never ran this good. My gas milage is way up, I'm guessing about 6 MPG. Hesitation is gone. I will look at moving the sensor to a more perminant spot as the AC compressor lines are not likely the best. But I did prove out what I suspected all along that my timing was being adjusted out of wack from the engine knock. Thanks to all that replied and I hope this post helps someone down the road.

Todd

[Blue Bowtie]

If you think it's a really bad lifter, you might want to check the rockers:



This one came into my garage running, driven from about 18 miles away, and the driver said it had a "pretty bad miss" along the way.

Yeah, ya THINK?

[manicmechanix]

Wowsers Bowtie Blue. What do you want to bet someone changed the intake manifold gasket and didn't properly torque the rocker arm bolts .

[tcopes]

I actually went back in and changed out the rocker arms and push rods on the front bank but still a knock. I believe it is coming from the front middle cylinder and is either piston slap or a wrist pin but I can't determine which. I will continue to drive it until I put a rod through the block or something to that effect. This is my ride to work, 100 KM each day and I am done putting money into this thing. I am just happy to be able to drive this thing normally instead of having to put it to the floor to get it to accelerate.

[AllGM]

Hello,
The problems you were having sound exactly like what I'm having now. The knock, the hesitation, no CEL, etc. Where is the knock sensor located? What do you mean when you said you grounded it to the AC lines?