97 K1500 multiple misfire problem

[v8_ranch]

We have a 97 K1500 Suburban with the Vortec 350. It has 210000 miles. Within then last 4000 miles, I changed the plugs and wires. Also, fuel pump was just replaced (with a new Delphi unit).

Recently, an SES light started coming in intermittently. I had it checked on two different occassions at autozone and it is showed multiple misfires, but not a specific cylinder. I went ahead and put new plug wires in again (lifetime warranty) and no change. Here is the rest of the info:

- Takes 2 or 3 tries to start
- Runs a little rough at idle (and now has smelly exhaust, not really rotten eggs, but maybe stagnant water smell???)
- Driving around town it tends to stumble a little when first applying gas,but then smooths out under harder acceleration
- Driving on highway, it is fine under hard acceleration, but if you have to slightly increase speed at any time, you have a bad stumble until you get onto it.

Please tell me this is unlikely to be the fuel pump again.I am so sick of that whole mess (replaced 2 in the last year).

I am heading to autoparts stores again to see if a new read on codes will turn up anything different.

Thanks

[777stickman]

Check the distributor for wear. Do this by removing the cap and try to rotate the rotor back and forth and side to side. Any play at all means you need to fix or replace the distributor. There may be other factors involved in your troubles, but this would be the 1st thing I would look at with the mileage you have on it.

I've never been to A/Z for a scan check as I have my own. I think they will just read generic codes. A good independent repair shop will have a high end scan tool (not just a code reader) that can tell what cylinders are misfiring and how many times.

We can't tell you anything about the fuel pump without proper pressure readings.

Do a search for MT-2500's fuel pressure reading guidelines.

[grumpy5]

What brand plugs did you put in? The bosch plugs will make the truck run rough. Try the AC Delco plugs. Did it start running rough right after you changed the plugs and wires?

[aztecf]

Change the dist cap and rotor.

JEFF

[manicmechanix]

I would bet the fuel injectors are dirty or maybe going out. the test for this is a cylinder drop test and injector coil test. Problem is that requires test equipment or taking it to a shop. You could test the injector resistance from the 10-way injector harness connector and run a big bottle of techron through the gas tank.

[v8_ranch]

Update:

Been terribly busy at work and finally getting back around to this. I ran a can of seafoam through gas tank and oil as well. Have several miles on since then. Yesterday though, the car started running a lot rougher while driving. You start to really notice it between 25-45 mph, and it almost feels like you are driving over the wake-up divets on the side of the highway. I still think it is probably a mis, but now wondering if it could possibly be tranny related. Sitting with car in park and revving up engine, there is no miss whatsoever, but you put it in gear and get up to about 25 mph, and it is extremely noticeable (shakes or stutters). Get back up to highway speed and still seems to smooth out under hard acceleration, but then as soon as you let off gas and then feather the accelerator, you notice a stumble again.

I went ahead and changed the distributor cap and rotor since it had not been done in a while. No change though. I then found a burned #5 wire and thought "Bingo!" Wrong again... dang. So the only thing on ignition that I have nto rechecked (as far as maintenance stuff goes) is plugs. I am waiting for car to cool off and then I will go ahead and pull those out to have a look. I am still getting a gas smell from exhaust, like gas is not getting a full burn in engine.

Someone mentioned the resistance on the injectors, what should they be reading?

Thanks

[chuck's]

The smell of gas could possibly be the temperature sensor.If the sensor tells the computer that the engine is cold when it really isn't,it would cause an over fueling problem ,hence the smell of gas.
chuck's

[v8_ranch]

Originally Posted by chuck's

The smell of gas could possibly be the temperature sensor.If the sensor tells the computer that the engine is cold when it really isn't,it would cause an over fueling problem ,hence the smell of gas.
chuck's

Do you mean the thermostat, or is there another sensor I need to look at? Also, can someone tell me how to check the TPS? I thought I saw it somewhere once, but cannot find it now.

[v8_ranch]

I put new AC-Delco plugs in this afternoon. The number 6 cylinder was all caked over nad number 8 was only slightly better. The rest of them looked OK, but I went ahead and put in all new AC-Delco plugs (the good ones - $5 a piece - ouch).

Drove around a while and still have the "shakes" between 25-45mph. I do not notice it at all until about 25 mph, and I can't really tell above 45 mph. But between the 2, man is it noticeable. It is most noticeable when lightly giving it gas. The more gas the less noticeable. When in that speed range, and I give it light gas, it feels like the wheels are about to shake off the car, but when I let off the gas, it is smooth again (there might be a slight 1-2 second delay before it is totally smooth). And then as soon as you give it the light gas again, back to the "shakes" again. As I was driving it this last time, I was kind of wondering if maybe I have had a couple of different problems. Could this "shaking" possibly be a bad u-joint? Been a while since I have had a car with a u-joint problem and so my mind is a bit rusty on what it felt like. I was just trying to think of drivetrain items that might cause this problem, as it idles and revs fine while sitting still in Park. I do nto think it is tranny or I would probably feel it even without applying the gas. Same with an out of balance wheel I would think. Just scratching my head aloud here. Please let me know if you think I am going down the wrong path or off-base on my recent thoughts.

[manicmechanix]

It kind of sounds like the torque converter lock up slipping, although 25 miles an hour seems a little low for it to start engaging. Does it do it if you place the transmission in 3rd or 2nd at those same speeds?

[v8_ranch]

Originally Posted by manicmechanix

It kind of sounds like the torque converter lock up slipping, although 25 miles an hour seems a little low for it to start engaging. Does it do it if you place the transmission in 3rd or 2nd at those same speeds?

I will try that out tomorrow morning. thx

[chuck's]

The coolant sensor should be located near the thermostate housing.It has a two wire connector.You could do a resistance check of the sensor when the engine is cold and then check it after the engine has been warmed up.There should be a difference in these readings.I don't know what the actual specs are but this will tell you if there is a change.Do these checks without the engine running and key off.
chuck's

[Jeremy-WI]

Check the distributor gear for wear

[j cAT]

Originally Posted by v8_ranch

I will try that out tomorrow morning. thx

the plug wires need to be measured with an ohm meter for proper resistance your eyes are not suffecient....


also at this mileage the distributor may need replacing as mentioned earlier... if the rotor in the distributor is wobbling around this wil cause your problem as well ,,,,, and many have found this the issue with the missfires..

[v8_ranch]

Originally Posted by j cAT

the plug wires need to be measured with an ohm meter for proper resistance your eyes are not suffecient....


also at this mileage the distributor may need replacing as mentioned earlier... if the rotor in the distributor is wobbling around this wil cause your problem as well ,,,,, and many have found this the issue with the missfires..

I understand what you say with the resistancxe check, but this was a case in which one wire was physically burned through the insulation (came loose from harness).

My shaking problem did turn out to be the u-joints. I have not had the SES light back on since the wires and plugs were changed, so keeping fingers crossed.

Still a little hard to start (takes 2 tries typically) so I am going to get back into the fuel system checks... AGAIN.