Can you diagnose this?

Any thoughts on what is causing this problem: When the engine is cold, there is full power throughout the RPM range, no matter the throttle position. When the engine reaches normal operating temperature, at low throttle / low RPM the engine runs smooth. At about 40% - 100% throttle between 0 - 4000 RPM the engine lacks power and bogs, though RPM's still rise at normal speed. And at 40% - 100% throttle above 4000 RPM the engine smooths out and has full power again. What does that sound like (for any tech's out there, or anyone who has had the problem)?

Any thoughts on what is causing this problem: When the engine is cold, there is full power throughout the RPM range, no matter the throttle position. When the engine reaches normal operating temperature, at low throttle / low RPM the engine runs smooth. At about 40% - 100% throttle between 0 - 4000 RPM the engine lacks power and bogs, though RPM's still rise at normal speed. And at 40% - 100% throttle above 4000 RPM the engine smooths out and has full power again. What does that sound like (for any tech's out there, or anyone who has had the problem)?

Throttle Position Sensor (TPS) perhaps? Sounds exactly like something that happened to my Grand Am about a year ago. Word of advice--if you have it diagnosed and the TPS is the culprit, by all means try to change it yourself. Shops charge a hefty penny for the replacement and it's relatively easy (to a degree).

--Jay

Hmm, well if it was TPS wouldn't you think it would have rough idle, and wouldn't it have loss of power all the time, not just when it warms up. BTW my exhaust had a small leak in it which I closed up yesterday, I noticed that the power loss decreased a little bit. It still bogs out, a lot, but less than before. One of my header's has a broken pipe on it, one of the pipes that come off the header, not a main pipe. And I can't remember but I think the problem started when I welded the converter on to replace bolts. I don't know if any of that might trigger something in anyone's head as to what the problem might be. And don't worry, on this car I do ALL the work myself...good learning car.

yeah im startin to have that same problem....When I press the gas about 3/4 the way the gauge will drop very little and then keep going like it should. I dont really know what problem this is so if they help you then it will probably help me.

But anyways I tried cleaning my fuel system because that was one idea to me. That worked for a little while but is still doing it so its not the problem.

Im hopein that its just an easy to fix problem. So I dont have to go all out on it just yet. But also my engine has 98000 miles on it.

the tps is know for going out in grand am's i reccomend you change it mine went out and i changed it and the whole thing smoothed out, its located on the side of the throttle plate (body) it takes two bolts to remove and is easy to replace it runs about $30, it worked on mine, try yours, Good Luck, the car will run rough when it cold anyways they are made to run warm and thats why they reccomend you let the car run for approx. 3 to 5 mins before driving it, Good Luck

the car will run rough when it cold anyways they are made to run warm and thats why they reccomend you let the car run for approx. 3 to 5 mins before driving it, Good Luck

Oh you must have read wrong, that's what's weird about this problem, it only runs smooth when it is cold, and rough when it warms up. But thanks for the tip, i'll look into the TPS since a few people have mentioned it so far and it's a pretty cheap part.

*UPDATE* I replaced a few vaccuum hoses and the breather thing that goes into the valve cover, and the check engine light went off. But the car still bogs out when it's warmed up. I'm starting to think the problem is an open loop, closed loop thing. Not 100% sure, but when the engine is warm, and I start it and floor it within less than 30 seconds or so, it has full power throughout the RPM range. Now my question is, are there any sensors besides the oxygen sensor that don't send a signal until the car is warm or after a certain amount of time (open / closed loop)?

have you flushed transmission???

nope I was thinking about doing that and changing the rear diff. oil but I didn't think that was causing the problem, since it runs perfect when its cold...seems more like a sensor problem. But if you know something I don't please tell me.

well the filter could be clogged becasue this guy i know was talkin to me about what all could be wrong and he said that it could be unbalanced tires ( dont ask ), the transmission could need the filter and new fluid, suspension, or the engine mounts.

I can kind of see how the transmission fluid might be it, but I don't know about the rest. I know my U-joints on my driveshaft are almost no good. But that all seems like it would be a problem all the time, not just when the engine warms up.

ok here are some sudgestions: assuming its an automatic, have the tranny flushed anyway, then u can zero out that posibility. part of it may be the temp guage, on my 90' formula if it gets to a high temp, the computer reduces the ammount of gas going into the engine to reduce the ammount of heat being produced. then again it could be the mas air flow (MAF) sensor, or the O2 sensor. another sudgestion is to check the vaccuums on the valve covers and if it has a carb, check the vaccuum there as well. it may be loss of compression also (check the head gasket and other pressure seals.) it may also be a bad ignition system or a cam problem (check distributor cap, rotor, and cam.) it might just need a simple tune up. you also might want to check your fuel pressure. i had a similar problem with mine, it idled fine but when i let off the clutch just enough to nudge the car forward, it boged or died. it turned out to be the fuel pump, and because u mentioned patching the exahust leak, if you had it on drive up ramps or the car was sloped so u could get under it and u start it up at that angle a few times... well there goes your fuel pump. pray that its not because unless u have a lift that u can use to drop the back end and get the fuel pump out, ur looking at a hefty mechanic fee. it cost me 300 for the pump without instalation and can go up to thousands of dolars. check your fuel lines for clogs. check your speed sensor also, it prob isnt the prob but its worth checking. you can usually tell its bad when the car wont shift itself untill 30 or 40 mph. u may also want to check the oil in the car.

It sounds like it could be the temp sensor. Very cheap and easy fix. Try it.

I would also check your EGR valve and make sure its still working properly. When your engine is cold, reach under the valve and push up and down on the diaphragm. You should be able to press the diaphragm up and down by using moderate pressure. If it doesn't move or takes a lot of pressure to move, I would replace it. I would also replace your PCV valve and possibly replace the fuel filter if it needs it. This should give a little better response. PCV is around $2, fuel filter $5, EGR valve around $35.

The EGR feeds small amounts of gas back into the combustion chamber. The valvue is usally open when your engine is warm and anytime your engine is running above idle speed. The ECM uses information from the coolant temperature, throttle position sensor, and manifold pressure sensor. The EGR valve should turn off at full throttle, if its still open, it could be a factor in robbing some power.

It could also be a clogged catalytic convertor.

So basically what you're all saying is it can be anything and I should check every damn sensor and mechanism in the car. lol

*UPDATE* Well since one of the possibilities of the code the engine threw was ignition timing, I decided to set the timing today. And to no surprise it is 2 Degrees advanced (its at 8 BTDC and it should be at 6). Now I know some people advance their timing to get some horsepower, but that's less than a degree isn't it? So would 2 degree's over be way too advanced and cause power loss problems or should it not effect it too much? (still new to timing)

Sorry if this posted there somewhere but I gave it a quick once over and don't see which year Firebird and Engine you have?. To know whether or not it will be too much timing but to tell you the truth most cars 2 degree's advance will give you better performance not worse and alot of newer cars don't allow you to adjust the timing but even while older versions of Fuel injection system allow you to adjust timing they will set off the Check engine light if your out of correct operating range

hmm I guess you're right about that, I can't get to the distributor hold down bolt anyway to change it, bought the distributor wrench but it doesnt have room to turn, guess i need a special one...its a 88 L98 350 by the way. Well now i just cant think of anything that it could be...egr maybe? (i dont know what it does but i remember turning an ajustable valve on the fuel rail before)

OK I just want to clarify all the problem's your having before I try to take a stab at what it could be.
1. Your setting a code for Maf.
2. Your setting a code for Ignition timing.
3. Your car stumbles.
Anything else you can tell me?

Well now it doesnt throw a code at all, vacuum loss was one of the codes and I had a bad hose that I replaced and the light went off. BUT, the code that it WAS throwing was #1. MAF Sensor #2. Ignition Timing #3. Vacuum loss #4. can't remember. The car does stumble, but only when I get on the gas, and only when the engine is warm. If the engine is cold then it's smooth sailing and full power.

Ok thats weird it threw a MAF code though. Because they should never be out of range. Even if your getting no vacuum and that would cause a stumble problem. Have you unpluged it recently?

check your spark plug wires for me, sounds like a misfire from a melted wire becsause it usually wont arc from the melted wire unless u floor it because that causes it to send a more powerful spark through the engine.

wow thats a long sentence :D

Try the temperature sensor. Mine was doing that (stumbling when warmed up and fine when cool.). The part is like 8.00 at auto zone 5 minutes to put in. its located at the front end of engine. I thought my car had a vaccum leak and then I tried replacing the wires ... that kinda helped but then i replaced this sensor and the car is fine and throwing no codes. It sounds weird but try it.

Try the temperature sensor. Mine was doing that (stumbling when warmed up and fine when cool.)

Now that's the first answer that sounds like it could really be it, but there's a few different temperature sensors in the engine do you know specifically which one it is?

For everyone else the car IS throwing a code still and it is: short or open circuit at MAF sensor burn off circuit. Theres a seperate code for a faulty MAF sensor, this is just a short at burn off circuit, which I don't know what that means, so does anyone else know?

check your spark plug wires for me, sounds like a misfire from a melted wire becsause it usually wont arc from the melted wire unless u floor it because that causes it to send a more powerful spark through the engine.

wow thats a long sentence :D

It's the opposite of what you're thinking, its only fine if I don't floor it, and "misfires/chokes" when I do floor it.

First I will explain the operation of a mass air sensor. How it works is it sends a set voltage to the maf wire those thin wires in the center somewhere between 5 -12 volts and then the incoming air cools down the wire lowering the voltage. The computer measure this voltage and determines how much air is coming into the intake. It then uses this information to calculate the amount of fuel needed to create the correct Air/Fuel ratio. With that said you either have a ground wire broken or accesory power wire broken and this would without a doubt cause your engine to run crazy do to it not being able to correctly create a fuel map for incoming air.

Ok thats weird it threw a MAF code though. Because they should never be out of range. Even if your getting no vacuum and that would cause a stumble problem. Have you unpluged it recently?

Actually yes I did unplug the MAF, and accidentally drove with it unplugged for a little while...but this problem was happening before that...one of my friends was messing with my intake once before the problem came up (I don't know if it was right when the problem started), but I think he just took the air intake tube off of the throttle plate, nothing more. Why? does that mess up something by unhooking it?

First I will explain the operation of a mass air sensor. How it works is it sends a set voltage to the maf wire those thin wires in the center somewhere between 5 -12 volts and then the incoming air cools down the wire lowering the voltage. The computer measure this voltage and determines how much air is coming into the intake. It then uses this information to calculate the amount of fuel needed to create the correct Air/Fuel ratio. With that said you either have a ground wire broken or accesory power wire broken and this would without a doubt cause your engine to run crazy do to it not being able to correctly create a fuel map for incoming air.

Hmm that sounds about right too, and that would probably be the short in the MAF burn off circuit...well i'll have to go through the wiring from the MAF sensor tomarrow, i'll tell ya if I find anything. Thanks for all ur help BTW.

The reason I asked that is because I have seen a thousand people that aren't careful when putting the plug back in the MAF and put it in on a angle and damage the prongs that hook into the clip which would cause your problem.

Well it barely reached and I wasn't too careful so that IS a possibility lol.

Well hopefully you will know tommorow. Good luck hope its just a broken wire or prong you can just bend back into place. Those would be free/cheap fixes

code 36 ? MAF sensor burn-off voltage was missing. Check MAF sensor burn-off relay and terminal "D" on MAF

Could be map sensor connection(most likely),
relay(3)You said only when it gets hot. Relays build more resistance when hot. Is that when the SES light comes on also ),
or faulty Ecm.

Read your private messages...

automan, u misread, i was talking about a misfire when u floor it

Well it is the coolant sensor. I had to remove the air filter where it connects to the engine cause it was in the way. If i remember correctly it was right below that. (by the way the engine I had was a 350 L98 I believe) Coolant drains out when it is removed. The car I bought .. well the exhaust fell off and then it was throwing oxygen sensor codes and such. WHen exhaust was fixed then it still stumbled and this was the problem. I tried to post this answer 5 min earlier so if there are two answers on here from me then i appologize. Let me know if it works!

automan, u misread, i was talking about a misfire when u floor it

oh sorry, HEY my car is the same exact car as your pic, color and all.

Well hopefully you will know tommorow. Good luck hope its just a broken wire or prong you can just bend back into place. Those would be free/cheap fixes

well you hit the nail on the head about the prong...there was a bent prong in there that wasnt plugging in...I fixed it but unfortunately the code still came back and the problem still remains.

code 36 ? MAF sensor burn-off voltage was missing. Check MAF sensor burn-off relay and terminal "D" on MAF

Could be map sensor connection(most likely),
relay(3)You said only when it gets hot. Relays build more resistance when hot. Is that when the SES light comes on also ),
or faulty Ecm.

Now you seem like you know about this problem. I don't know what it means when it says "burn-off voltage", could you explain that to me? And you wouldn't happen to know where the burn-off relay is? Also what would I be checking about terminal "D", just to see if it is connected? lol I suddenly feel like I know nothing. The SES light comes on a few seconds after the car is started usually. It's random, if it doesn't come on at start-up then it doesn't come on at all. But if it does come on at start-up then it stays on until the car is shut off. And yes it's code 36. I'm gonna do some more reading in the Haynes manual but anything that you could explain I would really appreciate.

well you hit the nail on the head about the prong...there was a bent prong in there that wasnt plugging in...I fixed it but unfortunately the code still came back and the problem still remains.
The connection now might not be good after the prong bent. I would switch your MAF with another person's if you know anyone else with a V8 GM MAF Fuel injection system. Lots of models use that same type MAF. Then you would know for sure it was the cause before you bother worrying about finding a replacement.
John

The connection now might not be good after the prong bent. I would switch your MAF with another person's if you know anyone else with a V8 GM MAF Fuel injection system. Lots of models use that same type MAF. Then you would know for sure it was the cause before you bother worrying about finding a replacement.
John


Hmm, good idea I never thought to do that...i'll have to try to find someone, can't think of anyone off the top of my head, i'm sure someone I know has to have the same MAF, what do you make of what tominajar said formula?

He know's what he's talking about but I disagree about code 36 (a MAF Sensor code) being a MAP sensor connection problem because if it was the MAP it would set a map code 1. and 2 even though the 2 sensors use each other as a reference for incoming air they have a preset value that they should never operate out of and if the Map sensor was malfunctioning it would be present on its reference voltage not the MAF.

I do agree that it could be faulty ECM though. All your problems are what happens when its on its way out. It throws alot of codes and cause's timing and injector pulse problems.

I'm beginning to lean towards the ECM being faulty too, I took it out yesterday and it's a remanufactured one so who knows. As far as the MAP sensor, my manual says that my engine doesn't use a MAP sensor (V8 TPI) so that can't be it.

Yeah I didn't think the TPI's ever used both but I know my LT1 does so I figured who know's . Most vehicles if its speed density its got a MAP and if its Mass air system well it has a MAF but some cars like mine use each other as a reference for getting proper A/F.

my car has basicaly the same problem and doesnt realy pick up speed quickly at all ... she just overheated last night and blew the intake manifold gasket seal and when i start her up cold she starts to idle and bogs down and stops unless i sit there for like 2-3 minutes and rev her hard to like 3000 4000 rpms

Sound like a bad vacuum leak to me but could be lots of thing's. Have you had the computer scan?

yeah it would seem they cant scan my car its tempermental they said i would need to jump key it and then see if i still got the same problems after that was done

jump key it? Never heard that term before. Also if your computer is giving error while trying to scan it you without a doubt have a bad ECM.

same here thats why ive been confused as to where to get one ...whats an ecm and how much does it run...

are you sure they didn't say jump terminals?

ECM stands for Electronic control module its your computer and I'm sorry I didn't relize your the same one from the other thread but a broken gasket will cause a real bad vacuum problem . You know this right>?

Which gasket? because if thats the intake manifold gasket then I think I may have pinpointed the problem.

thats the one alright its my intake manifold gasket that blew out on me yesterday and i also found one of my vacume liine sliced when i started to tear down the engine to replace her tonight and i broke an old line and the idle clip that holds the idle sting to the spring also broke the idle return bars clip that holds it on at the same time....

Which gasket? because if thats the intake manifold gasket then I think I may have pinpointed the problem.
I was responding to someone else I don't think thats your problem.
John

Well when I think about the life of my car since i've owned it, the only thing that has gone bad that hasn't been replaced is that gasket, and my problem seems like it could be vacuum. I have coolant boiling out of the intake manifold gasket, which means air can get in or out when it shouldn't. Maybe when the engine is cold the seal is just good enough to hold vacuum and when the engine warms up the metals expand apart which allows for vacuum leak, hence the loss of power?? does that seem feasible?

You could have abut I don't think thats what it is and also if you have collant leaking thats doesn't always mean that you have a vaccum leak it just means that the gasket broke around the coolant surface or that while your driving a broken hose or fastener was leaking and driped coolant which made its way back there. But its always a good idea to check all possible cause's and that could be one. I would buy a vacuum gauage and test if you suspect this is it.
John

Well it's definitely coolant boiling out of there, but a vacuum test would be the best way to go...i'm just really strapped for time and don't have too many chances to work on this.

Anyone think it could have something to do with the rear diff.? I could almost swear the problem started when I went WOT and it shifted hard into first, there was a weird noise from underneath and behind after, but it went a way after a few minutes.

Your rear won't set that type of code. and wouldn't have those symptoms

ok just checking, i dont know if i said this before, but that code has been setting itself on and off since I bought the car, and I never had any problem with power loss before. Probably should have said that before. *oops*