popping exhaust


jamestrow
03-13-2007, 07:24 PM
am new on this site, glad I found it, appears to be well informed. I have a 1988 Trans Am w/ a Chevy 350 (1987) TBI. Two weeks after purchase it drove me to the Pontiac dealership by request. They recommended another shop so we went there. The shop spent 4 days treating it believing it was a 305, at my final request and plea he finally concluded it was a 350. after this guys expertise and 5 days of changing; the timing chain, distributor shaft, harmonic balancer, adjusting the valves, egr sensor, ecs sensor, spark plugs, computer board, and many other things the car ran worse and my wallet felt equally pained. A few days later I randomly went to another shop and the mechanic noticed immediately it was a 350, listened closely and swapped the map sensor and it was fixed. Amazing. This was done 5 years ago and it has been reliable, 3 three years ago I had the lifters, cams and valves changed. Ok that being the history, here is the present; three months ago I noticed a pulse while driving, meaning a micro go/stop. Not a miss. No audible, just a micro pulse, the common person would not recognize it. Although the gas gauge did. I took the liberty and changed the plugs, rotor, cap and wires, no change. Trouble light time, first code running rich, the visual was the black path beneath the tail pipes standing still, I examined the EGR, ok, I changed the Oxygen sensor, ran better for a couple of days. Then second code, changed the Map sensor and the computer board, ran different, better? No, that is when the idle started to become erratic. Car still running rich. The popping started weeks ago and it is most obvious on a cold start, in Savannah a cold start is around 50 plus. The popping does not go away when warmed, the pulsing is still evident. Just today I got a code 23 and 54, fuel mixture sensor. Never saw that one or two before, never, I donít trust that error yet. The problem I am up against is each and every time I change something and reset the computer I need to drive 50 miles for the computer to do its readjusting. Back to the popping from the exhaust, my gut feeling says a cylinder or two is misbehaving. That being the case on a cold exhaust it could not be combusting in the pipe chambers near the rear. I pulled the two front plugs and they were tan in color, lean? If I could understand the popping I might be getting closer to the problem, no one around here has a clue and I donít trust the shops anymore, they ainít like they were when I was youngerÖ.. thanks for your time, James

wrightz28
03-14-2007, 01:46 PM
Welcome to AF :wave:

I'd love to help you out but, please edit your post to normal font and size so it can be read.

Thanks.

wrightz28
03-14-2007, 02:28 PM
James,

When you replaced the "computer board", do you mean the PROM chip? If so, is it correct for a 350? I ask becasue I believe the DTC 54 like a few others are multiple reason codes with one being a ECM fault.

Have you personnaly had the valve covers off and poked around?

jamestrow
03-14-2007, 02:39 PM
the chips were transferred to the new computer. the only reason I changed the computer was to eliminate that as a possibility, there was no change in performance because of that....

jamestrow
03-14-2007, 02:45 PM
the valves were replaced along with the lifters and cams a few years ago. prior to the problem of running less than normal it ran fine. 18 mpg in city and 25 on the high way. one day it started to misbehave, and since then I have been pulling codes and changing sensors. today I was under the hood and noticed the TBI injectors closely, the driver side injector appears to be dripping gas and the passngr side injector is misting it on delivery....

jamestrow
03-14-2007, 03:05 PM
to answer the valve cover off, no. I am not a mechanic. If if was to take off the covers, what would I be looking for? or what might you suspect? I don't hear any audible unusual noises in that area. there is simply a fluctuation in the rpm, mostly on idle, it still has get up and go, chirps in second, no hesitation on flooring it. I have dropped injection cleaner twice into it, adjusting the timing seems to be moot, keep directing your questions towards me and I wwill do my best to answer. I will fix this myself, or with the help of a friend if possible. Years ago when the map sensor was changed and it solved the problem, it cost me 240 bucks for an hour of time, the item cost 40 bucks, that stung, and I don't want to play that tune again... thanks

wrightz28
03-14-2007, 03:23 PM
mm kay, we fixed the text issue for you once, and you put it back. :dunno:

I was thinking maybe a craked rocker arm or bent push rod.

wrightz28
03-14-2007, 03:53 PM
Yeah in the quick reply box here at the bottom, there should be no font of size in the dialoge box, but that does not explain why it keeps coming back on your first post of the thread:

"Last edited by jamestrow : 03-14-2007 at 02:49 PM. "

wrightz28
03-14-2007, 04:06 PM
James,

all of your posts are reading that they have been edited all within a minute of each other.

why are you going back into them when they were fine and chagning them> What are you using for browser?

wrightz28
03-14-2007, 04:25 PM
Okay, that's better now.

The injectors should have a nice cone shapped spray patter to them.

jamestrow
03-14-2007, 04:30 PM
ok, good, back to normal. Don't know what went awry. as said before one of them is 'dripping', what impact / effect would this have with what I have decribed as a symptom described thus far? thanks for your patience and knowledge....

wrightz28
03-14-2007, 04:36 PM
The dripping wuould be no better than a bad jet on a carb. The droplet of fuel will not provide for very efficient combustion. It would idle poorly, but popping through the exhaust? Not so sure there. oddly enough, the 88 GTA we're buying has a pop in the exhaust when you feahter the throttle. It's TPI injected tho, weird.

jamestrow
03-14-2007, 04:43 PM
my initial observation of the dripping is it is a greater amount than the adjacent injector. if that is the case, richer? computer attemting to adjust that by bringing it down and thus cutting the other one too much and then runnning too lean? therefore the up and down idle?

jamestrow
03-14-2007, 04:45 PM
another question...timing, any impact on the popping? the EST, is that something having any connection with this?

wrightz28
03-14-2007, 04:50 PM
my initial observation of the dripping is it is a greater amount than the adjacent injector. if that is the case, richer? computer attemting to adjust that by bringing it down and thus cutting the other one too much and then runnning too lean? therefore the up and down idle?

See that's what throws the loop here, if it were lean then it would backfire through the intake.

jamestrow
03-14-2007, 05:04 PM
no intake back firing. any vacuum line specifically and possibly causing this? this afternoon for kicks and thrills I opted to twist the distributor and alter the timing, does this change anything or does the computer over ride the attempt? since the twist the start is not as smooth but the ride is better, frisky pick up less popping but too soon to say because I have not put 50 miles on it for the computer to readjust itself. I still suspect its a sensor or a vacuum line or even a weak electrical connection, any bodies guess. I don't think paying to have an analyzer is going to pin point it. using a combustable detector have any use? exhaust or other points? thanks

jamestrow
03-15-2007, 12:26 PM
latest attempt....I changed the temperature sensor placed inside the air cleaner housing, the engine seems to run smoother, the idle is jumpy, up and down but the engine sounds noticebly smoother. question, in my vane attempt to change the timing I notice where I can place it and where it definately does not belong, is this action actually sticking or is the computer going to over ride said action? an how might I up the idle speed? in the good old days it was a turn of a screw..... thanks for your time and interest... James

wrightz28
03-15-2007, 12:38 PM
Yeah, never 'bump' the timing on distributor these days. You need to put it back where it belongs by disconnecting the tan wire on the firewall pass. side. loosen up the hold down, install your timing light and return the timing to normal. A few degrees adv. will give you e a little "extra" respone, but nothing excessive,.

jamestrow
03-15-2007, 01:00 PM
I need some specifics on the tan wire, (this engine was obviously changed by someone not necessarily doing it by the book) and the manual I have been following (haynes) was designed for the Trans Am, not the Chevy the engine came out of. Give me a route of where this tan wire comes from and where it goes to. On my passenger side is the plug connector to erase the error codes..... any specs will be followed closely, I can't assume the wire in this car is going to be tan..... thanks

jamestrow
03-15-2007, 01:05 PM
another thing I need to share with you, this is the first computer chip car I have owned. All preivious cars have been without the CPU in it, and guess what, I am a computer consultant. Upon fixing computers I actually walk away because the computer does not need to go through a 40 mile reset period, where as cars seem to. Prior to this car I was able to tune a car with my ears and a screw driver, those were the days, and the next car is going back to a pre 1970 again.....

wrightz28
03-15-2007, 01:17 PM
The motor that was in the car origionally be it a 305 (5.0) or 350 ( 5.7) was in fact a Chevy motor, so that should make no difference.

I do not understand why your data link connector would be in the engine compartment and not under the dash where it belongs.

jamestrow
03-15-2007, 01:26 PM
the link connector is under the dash board driver side, the connector I am referring to is the connector which erases the error code. But as you have been corresponding maybe it isn't. according to the repair manual I thought that is what is was, a single wire snap in connector? My 'assumption' was that connector merely ungrounded the storage of codes. kind of like a soft boot instead of a hard boot by removing the negative battery terminal.

wrightz28
03-15-2007, 01:33 PM
Ok, on the passgner side firewall there should be a single wire off the distributer heading to the pass. fender then through the firewall. This is the ECM timing ref. wire as outlined in the manual on how to set the timing. To reset the codes you merely disconnect the battery. :dunno:

jamestrow
03-15-2007, 01:38 PM
technical question; is the distributor cap designed to be installed 180 degrees either way? or in other words can it be installed backwards? another thing, I don't remember if I applied the lubricating paste on the center contact zone, what impact would that have? and back to idle climbing and falling, what causes that? obviously the computer is compensating for something, but what? back to the changing of the air temperature sensor in the air filter zone, the popping / burping is less significant, mostly significant when the RPM drops below 500, am I leaning towards a solution or just slowly replacing things not needed to be replaced, and just supporting the local NAPA?

wrightz28
03-15-2007, 01:57 PM
The cap only goes one way, there is a indent that must be matched up to the dist. base plate, if it wasn't it would be extremely obvious. You could just have a vacuum leak. But you need to get the timing back to stock first before trying to find anything else.

jamestrow
03-15-2007, 02:20 PM
you are definately on something here and I appreciate your knowledge and assistance, final question this day, the dwell setting for this engine, my research and not sure would be around 12 @ 2000, thanks again......

wrightz28
03-15-2007, 02:27 PM
Dwell be it in terms of fuel or spark is not an adjustable item on these cars.

The check engine light is not on?

jamestrow
03-15-2007, 02:52 PM
perhaps the wrong term, how about points advance off the fly wheel? the trouble lights most recent code is 42 (est) and 45 (running rich, oxygen sensor, egr, replaced both), but not the est yet....

jamestrow
03-15-2007, 02:54 PM
is it necessary to run the car 40 miles before the computer does its thing, and gets the bugs situated?

wrightz28
03-15-2007, 04:25 PM
The est code gets set when either the knock sensor signal is out of range or when the ECM ref. wire is/has been disconnected.

To reset the ECM, again, disconnect the battery for a few minutes.

jamestrow
03-15-2007, 04:48 PM
thanks wrightz28, back to my initial curiousity, the popping sound. where does it originate from, what is the cause. is it a combustion, a mechanical, or a thing getting through the muffler and not being phased out? knowing the audible would help know the origin. any ideas out there?

jamestrow
03-16-2007, 04:03 PM
todays episode based on yesterdays activities was car starts fine, no popping, idle stable at starting temperature, driving for ten minutes a slight pulse and a drop and correction. first stop idle erratic, power upon take off, nothing unusual for the next few miles, reached destination, idle still not popping, idle erractic but not as bad as previously. outside temperature upon start was 60 degrees. afternoon start, started fine no popping, cruising was smoother than morning, idle was still erratic, temp outside 76 degrees. the popping is not as evident by 89 percent less. why? temperature? humidity?, or some changes made? I have driven only 15 miles since I reset the computer and reset the timing. Back to the popping sound, what are the physics behind that noise? is the noise created in front of the chambers in the muffler or behind? is the frequency of the cause not able to be phased out? any body have a clue regarding this audible?

wrightz28
03-16-2007, 05:00 PM
It would be fuel ignting in the exhaust system from incomplete combustion.

jamestrow
03-16-2007, 05:24 PM
try this again, not the first time and all this typing becomes washed away because the site forgets I logged in. how does a combustion happen in a cold system? initial start, pipes cold and popping exhaust. the exhaust hot enough to light unignited gases in an area with carbon monixide and little oxygen? thanks

jamestrow
03-16-2007, 05:35 PM
my understanding is the timing or ignition has failed to complete a thorough process, hence the unignited fuel combusting in the exhaust manifold resignating a popping noise. makes sense so far. whats left is the idle.. thanks for all the help.

wrightz28
03-16-2007, 05:37 PM
You said ine of your injectors is dripping, not spraying, that can do it.

BT- I am sigining off for the weekend, so if your going to try and troubleshoot it during that time I'm sure someone will help you out :cheers:

jamestrow
03-16-2007, 05:47 PM
now we are getting somewhere, I am taking the weekend off too, thanks and have a good one.....

Earlsfat
03-19-2007, 04:57 PM
the exhaust hot enough to light unignited gases in an area with carbon monixide and little oxygen? thanks

Was in mine - I don't think the actual exhaust pipes play much into it. The exhaust gases would be hot enough almost immediately. I do know that the exhaust pipes only take a few seconds to get hot enough to burn you (yep) so the gases themselves would be enough to combust any fuel in there.. especially given the proximity of the two.

On a side note... I guess that sort of tell you just how efficient the internal combustion engine is... you would think all the oxygen would be used. EDIT: Read someplace that a HIGHLY efficient engine runs in the 90% or so efficiency range.

jamestrow
03-24-2007, 12:03 PM
ok, based on that, unignited fuel, what are any causes or all of this. bad plugs, bad wires, seem to be the obvious, but I changed those recently, what are the other possibilities. so far I am not getting closer to this scenario. any suggestions will be appreciated.....

Earlsfat
03-24-2007, 01:10 PM
You said one of your injectors is dripping, not spraying, that can do it.

- AND -

Bad rings, burnt valve, hole in piston... Run a compression test / leakdown test on every cylinder... if they are all the same that's not you're problem. If you've got one or more that are different from the rest, you've started to narrow down your problem.


(IE Mine was supposed to be running 185-or-so psi per cylinder, had one at 120 and another at 15... Pulling engine to find out what exactly the problem is - bad piston, messed up valve (stuck open), or bad rings (this is most likely, from what everyone tells me)).

Sounds like you've determined that you're getting a spark to all cylinders, so that's not your problem. Need to start looking inside to see what's wrong.

Earlsfat
03-24-2007, 01:14 PM
Are you sure your plugs are gapped right?

I've smashed the gap shut installing plugs before... that'll do it.

jamestrow
03-24-2007, 01:37 PM
odd thing is the popping started before the plugs, wires, cap and rotor were replaced, no change. regarding the rings, pistons and valves, the valves were changed a couple of years ago along with the lifters and cams, as far as the rings and pistons go, would not there be a consumption of oil along with that, especially a holed out piston? I will have the compression checked though, at least that will add or remove a possibility. thanx

jamestrow
03-24-2007, 03:41 PM
putting the popping aside (a symptom), the idle being irregular, up/down; perhaps the computer making adjustments, does that fit with the previous comments w/ pistons, rings, valves? traveling at cruising speeds, a non-smooth hold on the power, a recognizable pulse of come and go, computer compensation? the power of shifting into second with the same ability to chirp as it has always? no lack of power when needed. no trail of smoke when punching it. does this fit with the compression thing? I need to ask these questions to remove the possibility. would a simple vacuum line be responsible for any of these errors? as mentioned before I found a frayed vacuum line coming off the tee of the EGR situated towards the driverside, looked for a connection, no avail, what unit might be there unconnected? would the EST have any cause for this malfunction? thanx again....

wrightz28
03-27-2007, 11:38 AM
While all this is going, is that injector still driblling???

Pull your oil stick and make sure that your opil is not contaminated with gas (also meaning the cylinders have had their lubricating oils washed away :eek: )

jamestrow
03-27-2007, 12:02 PM
I checked that, no fuel in the crank case. My initial thoughts when the holed out pistons, bad rings were presented was there would be a contrail of smoke behind me like the Blue Angels, there isn't. Since I reset the computer last week w/ about 30 miles on it, the code 32 came up, just that, so it points towards the EGR. Today and yesterday the popping is less and today none. The idle is jumpy and on the high way is a slight pulsing of jumpiness. Now if the EGR or the EGR Solenoid were to be faulty what would the symptoms be? I am not making any changes until I am convinced the computer has done its adjustments....What impact does weather have on this car, temperature, humidity and so on? thanx

jamestrow
03-27-2007, 03:39 PM
yea the driver side injector is still dripping not spraying, but I assume the volume is the same just the delivery is not. what if scenaio; the egr valve was not shutting completely? this would deliver a less than clean air into the engine at idle, right? I checked the egr solenoid and the vacuum at idle is none and at acceleration it delivers a vacuum. so if the egr was not closing completely that would make for a bad mixture, right? when I pulled it out the valve was operable, I just can't see inside of it. I went to NAPA to look at one but not a stocked item. the manual says it can be cleaned but not very clear on how. any solvents able to dissolve carbon?

Add your comment to this topic!