Help diagnosing two issues 1) misfiring/stumbling 2) coolant loss

[John03Z71]

My 2003 Tahoe 5.3 has about 270k miles. For the past year or two there has been a slight misfiring / hesitation on acceleration that has gotten progressively worse. Over this time period, I've replaced (not just due to this issue) plugs and wires, intake manifold gaskets, knock sensors, valve cover gaskets, PCV valve, O2 sensors, TPS, water pump, alternator, and some other unrelated parts.

So I've basically got 2 issues going on, one has been going on for some time and the other has just started the last few weeks or so.

#1) The misfiring has gotten very bad lately and is causing poor performance on acceleration, but only some of the time... kind of hard to explain so bear with me, hopefully this will make sense to someone. If I'm at a stop and accelerate gently and smoothly it's not really noticeable, but if I'm at a stop and have to step on it hard to get going real quick (i.e. waiting to turn in traffic and someone waves to let me go, or if a red light turns green and I don't notice it right away, etc.) it bogs down terribly and the engine stumbles so bad it sounds similar to tapping your index and middle finger back and forth on a desktop. It'll do this as long as I keep my foot down.... BUT, if I let off the gas pedal all the way and hit it again right away, its a 50/50 whether it will do the same thing again OR if it will haul ass and take off like a brand new truck. Even under normal / moderate acceleration I've noticed the same thing, if I get that annoying shaking/stumbling I can let off the gas and step on it again a time or two and usually it'll get itself going like normal.
Lastly, if I'm cruising at 55mph or so and come up to a slight incline, it'll try to keep itself going in the same gear but as it slows down I can hear and feel these random misfires, then it'll kick down to the lower gear. What could the culprit here be? No engine codes, any misfiring or air/fuel codes that have come on over the past year or two have been resolved by replacing O2 sensors and knock sensors.

#2) Over the past few weeks I've been smelling coolant around the engine area and getting a squeaking noise coming from my serpentine belt area on cold startups. No visible coolant under the hood that I can see. Low coolant level light came on last week so I dumped about a half gallon or so in the reservoir, and it just came on again today. The other week when I first noticed the issue I popped the hood first thing in the AM and cranked it up, and a puff of white smoke/steam came from the engine bay for a second or two and disappeared before I could tell where it came from. I haven't done any compression tests yet as I don't have the diagnostic tools. The engine does not overheat when it's cool / cold outside, sitting at idle or driving, but I do recall this past summer on hot days if I let it sit idling for more than 10 mins the temp would then creep up to 230-235ish... if I gave it some gas to get the fan cranking it would cool itself down, but would creep back up. (It never went over 235 (3/4 on the gauge), but I also never let it go further than that so no telling if it would have or not). It would also cool right back down to normal as soon as I started to drive it, and would stay at normal temperature under normal driving conditions even in the hot Carolina summer (95ish degree days). Even in traffic it wouldn't overheat, it would only creep up after sitting at idle for several minutes and only on very hot days. This could just be simply a thermostat, but just giving all the info I can in case anything else points to bigger issues or relates together.

Lastly, it could be unrelated and no big deal, but I've noticed now that it's cold outside that when I shut the engine off there is a small trickle of white steam/smoke that still comes out of the passenger side tailpipe for a couple minutes (after engine is shut off). I don't have true duals, I have a Flowmaster 10 series single in / dual out, so not necessarily saying it's related to one side of the engine or the other, but still odd that it only trickles out one side.

Sorry for the long winded post but I wanted to be as detailed as possible in hopes that someone can offer some insight. I love this truck and do 99% of the work on it myself. Thank you in advance for those who took the time to read and/or offer some advice.

John

 

[Scottydoggs]

with the high miles there, bet the cats are shot to hell.

 

[Doubeleive]

if you have not already replaced the maf at that mileage that could very well be your problem, anything above 160k and the maf becomes highly questionable.
the maf can cause all the mentioned issue's.
as for coolant loss, pull the oil fill cap off and look underneath it, look for any milky looking snot, the bottom inside of the cap should be dry and clean under normal circumstances, some may disagree with me but unless you drive down the block and back there should be nothing under the cap.

 

[John03Z71]

with the high miles there, bet the cats are shot to hell.

Thanks for the feedback. I'm doing some research to see if it's legal in my state (NC) to remove the cats, or if I have to replace them. Would much rather just cut them out but we have yearly emissions inspections.

 

[John03Z71]

if you have not already replaced the maf at that mileage that could very well be your problem, anything above 160k and the maf becomes highly questionable.
the maf can cause all the mentioned issue's.
as for coolant loss, pull the oil fill cap off and look underneath it, look for any milky looking snot, the bottom inside of the cap should be dry and clean under normal circumstances, some may disagree with me but unless you drive down the block and back there should be nothing under the cap.

Thanks for the info. Wouldn't the MAF throw a check engine light and code?

I just took the oil filler cap off and besides some slight oil residue it's dry, no milky snotty stuff.

 

[OR VietVet]

I agree with @Doubeleive and @Scottydoggs that it is definitely time to replace some parts due to mileage and I also think the MAP should be done when you do the MAF. I would also get a compression test done with all plugs removed and inspect the plugs when out. The cooling system needs to be pressure tested. You are losing coolant and a nasty looking oil fill cap with snot on it is a head gasket problem sign. At that mileage it is time to bite the bullet. The radiator may also be suspect for the loss of coolant with a seam leak or a crack on the tanks and the fan clutch may be suspect as well. A good flush of the entire system is needed while all is apart. So, 15 minutes of diagnostics and 1 hour of parts replacement and problem solved.

 

[Doubeleive]

Thanks for the info. Wouldn't the MAF throw a check engine light and code?

I just took the oil filler cap off and besides some slight oil residue it's dry, no milky snotty stuff.

that's why I said the maf is questionable after 160k, it may work just enough to not throw a code yet wreck havoc on everything, I am not saying go throw money at a new one but if you can a hold of a used known good working one I would try it and see otherwise you need a scanner and look at some live data to make a final determination, sometimes it's cheaper to just bite the bullet and replace but...it could still be something else entirely I just have been there and threw parts at a truck, new plugs, wires, coil packs, knock sensors, etc and still have issue's and after all that it was still the dam maf causing fits. now the maf is usually my first suspect seen them do all kinds of weird shit, lean codes, shift problems, surging, bogging, no start (turn over but not run), throttle body codes, misfires. A lot of stuff depends on that air meter data.

 

[Doubeleive]

if there is no coolant going in the engine then it has to be going somewhere, 100% of the time liquid flows down so you need to get a flashlight and get under the truck and look up. sometimes you cant find it while looking from above. put some cardboard under the truck overnight and look for wet spots in the morning.

 

[OR VietVet]

I just replaced my MAF, MAP and Crank/Cam sensors, just because and saved the old working parts for if needed or testing with. Wes, is correct. If you don't want to replace the MAF you can at least try to clean it with cleaner from the parts store.

Of course, if you do replace, use a GM or AC Delco part.

 

[John03Z71]

I just replaced my MAF, MAP and Crank/Cam sensors, just because and saved the old working parts for if needed or testing with. Wes, is correct. If you don't want to replace the MAF you can at least try to clean it with cleaner from the parts store.

Of course, if you do replace, use a GM or AC Delco part.

Thanks! I was going to pick up a can of cleaner from the parts store and try that. If that doesn't work, I'll swap the part out and see if that makes any difference. How much would you want for yours that you say is still in working order? Feel free to PM me.

 

[OR VietVet]

I don't want to sell it because I want it as a spare. I paid $133.79 minus 5% at RA for mine and is the GM one and is new. The one listed at RA for AC Delco is a reman and is $75.79 minus the 5% but both require a shipping fee. You can get a Delphi at RA for $88.79 and is new plus can also use the 5% discount..

 

[Gtir007]

Did you change the egr valve?

 

[Grebbler]

I've run into each of these; most when vacationing in warmer climates, and no codes were present. In short:

Overheating and hot stumbling was caused by a weak fan clutch. The added heat caused the crank sensor to act up. Sadly, the clutch replacements bought at auto stores were stiff and noisy as heck (woosh) and I ended up adding silicone oil to my old one to revive it a bit. Crank sensor still sitting in box on shelf.

Coolant loss seemed erratic but overflow tank that replaced one from a previous accident didn't have a working level sensor so I only noticed it while under the hood and started keeping my eye on it. Maybe a quart to a gal every month or so. No water in oil or puddles so I assumed a seepage at pressure directly into a cylinder. I added a pack of those crushable block sealing tablets to the coolant via upper hose a year or so ago and level has been steady since. If you haven't done a flush yet, do so if only to replace depleted lubricants and seal conditioners THEN add the tablets.

Occasionally I would get sudden oil loss. Randomly every few years a quart or 2 of oil would just disappear. I swapped the PCV valve to an orifice style and thought it was cured but it happened again recently - just took longer. No clue yet whats going on.

Agree with others to keep MAF clean. Spray cleaner and a q-tip or coffee filter on a stick.

Clean out the IAC valve and throttle body now and then. Run only OEM / NGK plugs.

Take advantage of auto store tool loaner program. Grab a fuel pressure gauge, compression tester, etc and see where you are. A $10 ELM clone scanner from Amazon/Ebay and a phone app like Torque is a great cheap way to get some live data to verify sensors and cats.

I also drilled small holes in exhaust just before cats to check for backpressure then sealed them with self tapping screws so they can be checked again. Use fine thread tapping screws like 10-32 electrical ground screws rather than a TEK or something used on your gutters. My cats are dead but not plugged yet.

Engine Restore (in a can) does work somewhat.

Good luck.

 

[Doubeleive]

if you throw on another MAF be sure it is the right one, I replaced the one on the wifes 05 i bought her last year when I was doing some maintenance when we first bought it and it hiccuped on me like a dam bucking bronco, I knew right right away what it was. hasn't done it once since.

 

[Tonyrodz]

if you throw a another MAF be sure it is the right one, I replaced the one on the wifes 05 i bought her last year when I was doing some maintenance when we first bought it and it hiccuped on me like a dam bucking bronco, I knew right right away what it was. hasn't done it once since.
View attachment 265526

Was it the GM maf that hiccupped?

 

[1BADI5]

Have you ever cleaned the throttle body............that is the cause of alot drivability issues with LS based motors.

New air filter?
Fuel filter replacement? I do them annually for cheap insurance.

Other items that can cause misfires on older/high milage motors: weak ign. coils and clogged fuel injectors.

Without any MIL/CEL codes to work with, I can only make my assumptions based off from what has been replaced or addressed up to this point.

 

[Doubeleive]

Was it the GM maf that hiccupped?

It was the transmission that hiccuped due to the maf giving erratic data, had it happen before on a 04 and 03 and a 00 the 04 took a while to figure out thought maybe the transmission was taking a shit it would do really weird stuff like you would be driving say 50mph, give it some gas and it would act like it was slipping and downshift into 2nd or 3rd then back to 4th and then if you just babied it then it would just keep on cruising normal. then other times it would drive just fine, after a while it FINALLY threw a maf code once. replaced the maf and it shifted perfectly afterwards and kept on working perfectly. On my 03 it would keep on throwing a lean code and other's I knew what it was because I had a modified performance maf and if you did not keep it clean constantly it would throw codes finally got tired of it and put a oem one back on and walla codes gone, on my 00 it would bogg down like it had no power you could be doing 50 punch the pedal and get nothing no power at all, no downshift nothing gutless...bad maf...
all those things led me to figuring out they start taking a shit at about 160k, on the 05 it was 154k (close enough).

 

[roadspatula]

John, just a thought , I was losing coolant in my 2003 and I could not find any coolant under the motor or radiator. Check the heater hoses where they connect to the firewall. Somehow both of mine were cracked and were trickling out of the fittings back toward the firewall and behind the sound deadener material on the firewall. I switched em' up and have not had coolant loss or smell since. Just thought I'd share.

 

[roadspatula]

My 2003 Tahoe 5.3 has about 270k miles. For the past year or two there has been a slight misfiring / hesitation on acceleration that has gotten progressively worse. Over this time period, I've replaced (not just due to this issue) plugs and wires, intake manifold gaskets, knock sensors, valve cover gaskets, PCV valve, O2 sensors, TPS, water pump, alternator, and some other unrelated parts.

So I've basically got 2 issues going on, one has been going on for some time and the other has just started the last few weeks or so.

#1) The misfiring has gotten very bad lately and is causing poor performance on acceleration, but only some of the time... kind of hard to explain so bear with me, hopefully this will make sense to someone. If I'm at a stop and accelerate gently and smoothly it's not really noticeable, but if I'm at a stop and have to step on it hard to get going real quick (i.e. waiting to turn in traffic and someone waves to let me go, or if a red light turns green and I don't notice it right away, etc.) it bogs down terribly and the engine stumbles so bad it sounds similar to tapping your index and middle finger back and forth on a desktop. It'll do this as long as I keep my foot down.... BUT, if I let off the gas pedal all the way and hit it again right away, its a 50/50 whether it will do the same thing again OR if it will haul ass and take off like a brand new truck. Even under normal / moderate acceleration I've noticed the same thing, if I get that annoying shaking/stumbling I can let off the gas and step on it again a time or two and usually it'll get itself going like normal.
Lastly, if I'm cruising at 55mph or so and come up to a slight incline, it'll try to keep itself going in the same gear but as it slows down I can hear and feel these random misfires, then it'll kick down to the lower gear. What could the culprit here be? No engine codes, any misfiring or air/fuel codes that have come on over the past year or two have been resolved by replacing O2 sensors and knock sensors.

#2) Over the past few weeks I've been smelling coolant around the engine area and getting a squeaking noise coming from my serpentine belt area on cold startups. No visible coolant under the hood that I can see. Low coolant level light came on last week so I dumped about a half gallon or so in the reservoir, and it just came on again today. The other week when I first noticed the issue I popped the hood first thing in the AM and cranked it up, and a puff of white smoke/steam came from the engine bay for a second or two and disappeared before I could tell where it came from. I haven't done any compression tests yet as I don't have the diagnostic tools. The engine does not overheat when it's cool / cold outside, sitting at idle or driving, but I do recall this past summer on hot days if I let it sit idling for more than 10 mins the temp would then creep up to 230-235ish... if I gave it some gas to get the fan cranking it would cool itself down, but would creep back up. (It never went over 235 (3/4 on the gauge), but I also never let it go further than that so no telling if it would have or not). It would also cool right back down to normal as soon as I started to drive it, and would stay at normal temperature under normal driving conditions even in the hot Carolina summer (95ish degree days). Even in traffic it wouldn't overheat, it would only creep up after sitting at idle for several minutes and only on very hot days. This could just be simply a thermostat, but just giving all the info I can in case anything else points to bigger issues or relates together.

Lastly, it could be unrelated and no big deal, but I've noticed now that it's cold outside that when I shut the engine off there is a small trickle of white steam/smoke that still comes out of the passenger side tailpipe for a couple minutes (after engine is shut off). I don't have true duals, I have a Flowmaster 10 series single in / dual out, so not necessarily saying it's related to one side of the engine or the other, but still odd that it only trickles out one side.

Sorry for the long winded post but I wanted to be as detailed as possible in hopes that someone can offer some insight. I love this truck and do 99% of the work on it myself. Thank you in advance for those who took the time to read and/or offer some advice.

John

John, It has a misfire and no codes??

 

[29tomt]

I agree about the MAF. My 2003 Tahoe same engine had a random idle miss, acted like a bad wire or plug etc and then would not crank but then did, etc. Gave random codes that cleared. It had done that for 5 years that I had owned the vehicle. Cleaning did not help. Finally my shop said replace it and I did and it has run like a new truck since with a smooth idle.