why won't my car accelerate after hot?

[bsconz]

So i bought this car and it turned out the entire fuel system needed to be replaced. i have completed that but i still have an intermittent problem with the car not accelerating. it seems to happen after the car has been on for a while when it's hot out...like on my afternoon commute home from work in stop and go traffic.

i feel like it's something to do with an engine sensor (mass air, O2, IAT, ECT), but could it be the evaporative emissions system or exhaust gas recirculation effing up the intake air?

i am pretty sure the engine is getting fuel and ignition. so it has to be something else. it seems like the computer is calculating the wrong a/f ratio. it never has this problem in the morning when it's cool.

i am stuck!

[somerandomdude]

Is the check engine light on?

[Binjammin]

Replace ENGINE TEMP SENSOR (12621288158) and make sure you are getting enough fuel pressure. Running worse as you heat up = too much fuel.

Not true at all. It could be something as simple as a bad set of plugs to a bad ecu. Running worse when you heat up doesn't mean too much fuel at all. That's not to say it *couldn't* be too much fuel, don't get me wrong, but too much fuel would only happen in very few circumstances.

The car thinks it's getting more air than it is.

There's a bad injector leaking down fuel.

Maybe a bad fpr.

OP, you say you have a problem with the car not accelerating, care to elaborate? Is the engine smooth running with no power? Does it run badly with a severe miss?

No e34 has EGR btw. Pretty sure that's not it.

[gtopaul]

Sounds like a typical stopped up catalytic convertor to me. Only happens when hot and when you give it gas it sort of falls flat on it's face and won't accelerate. Sometimes you can smell them, sometimes you can look under the car and see it glowing red, and sometimes if you just stand on it when it does that it will turn the check engine light on. Quick test to determine if it's the cat is to disconnect the exhaust at the down pipe and drive it. Yes it's loud but it will quickly tell if the cat is the problem or not.

[Isaacus]

If it still has power up top (when cold or hot) I'd doubt it's a bad cat. Does the power ever recover if you rev it higher?

Maybe you have a lot of carbon build up in the combustion chambers causing hot spots and detonation/preignition and it's setting off a knock sensor and backing off a lot of timing. That'd kill the power, but only when hot.

What gas are you running?

[Zukuri73]

Sounds like a typical stopped up catalytic convertor to me. Only happens when hot and when you give it gas it sort of falls flat on it's face and won't accelerate. Sometimes you can smell them, sometimes you can look under the car and see it glowing red, and sometimes if you just stand on it when it does that it will turn the check engine light on. Quick test to determine if it's the cat is to disconnect the exhaust at the down pipe and drive it. Yes it's loud but it will quickly tell if the cat is the problem or not.]

I was going to say Catalytic. Could also just be 02 sensor. When your 02 sensor is really really dirty, your car will be gutless. At least that's my experience. I hope this helps.

[bsconz]

Wow, thanks for all the replies! I will elaborate on this issue:

*

I have replaced the fuel injectors, fuel pressure regulator and fuel tank with recycled parts from Bavarian Auto Recycling. I replaced the pump with a new OEM replacement pump from TRE Performance. I also cleaned the throttle body and replaced the spark plugs with new NGKs.

I checked the IAT, TPS, and ECT sensors according to the Bentley Service manual.

*

The exhaust has a pungent smell to it. I want to say it smells rich but there’s definitely a funky smell coming out the pipes. There isn’t any smoke though. I am running 91 octane gas. What smell would a bad cat make?

*

When the problem happens, it feels like the engine is being choked for air. *It doesn’t feel like it’s misfiring or running rough, it just won’t accelerate. If I were to mash the throttle to floor it would just accelerate even slower. The check engine is NOT coming on. Before I did the fuel system replacement, the check engine light was coming on when this problem occurred. It only seems to happen when the ambient air temperature is over 100degF and the car has been running for a while.

*

Possible Causes:

*

Bad Cat

Bad ECT sensor

Carbon buildup/hot spots

Bad fuel pressure regulator

Bad injector

Bad plug(s)


Would bad fuel cause carbon buildup, damage the cat, damage the o2 sensor?

*

[Zukuri73]

Would bad fuel cause carbon buildup, damage the cat, damage the o2 sensor?

*

Bad fuel would certainly cause carbon buildup. As for what it damages, the catalytic converter yes, the O2 sensor? no. But it would cause the O2 sensor to change the oxygen to fuel ratio, and cause damage that way. All of this would take a LONG time of using bad fuels though. You don't fuse your cat over night. Also, if you have used any accelerants in your fuel or the like that could do it also, but this is still a gradual problem. Did this problem take a while to show up?



What smell would a bad cat make?
Hard to describe unless you've smelled it before. Kinda smells like what happens when you pour fuel on your engine block and heat it up to evaporate.



When the problem happens, it feels like the engine is being choked for air.

You have either too much compression or too little. From the funky smell coming from the exhaust my guess would be too little. You may have a hole in your cat somewhere. also, could be that the intake isn't bringing in enough. I could be completely wrong though, and you may have too much compression (caused by a faulty O2 sensor, fused Cat, etc.) if that were the case, you may still get the smell, but you would usually get backfires, (assuming you were trying to accelerate quickly).

[Meeve]

first step is to check your compression ratio. It's easy and you can do it yourself if you have the equipement. You may lack compression when engine is hot if piston ring are tired.

[somerandomdude]

Do a tap test on you're mass air flow sensor with open palm and use you're fingers to tap it. If the motor stalls or stumbles, you're maf is bad.

Also, inspect the vacuum hose.

[bsconz]

Which vacuum line are you referring to? Throttle body to fuel pressure regulator?

[somerandomdude]

That one, the 2 connecting to the intake tube and the one coming from the intake manifold to the iacv (witch is underneath).

EDIT: I wanted to ask. Doe's she stumble when you hit the gas after it reach temp or after a long drive? I know you didn't mention that, but I figure I'll ask.

[bsconz]

ok, i will check all of those hoses. i am pretty sure everything is fine there though. i checked all that when i took apart the throttle body and cleaned it.

yes, it kind of stumbles as you are describing. my afternoon commute is where i feel it the most. it just gets worse and worse. i'm buying a compression tester tomorrow after work.

[somerandomdude]

I think you can rent one at you're local auto zone for a fee and you get the money back when you return it.

When was the last time you gave her a tune up? plugs, boots (wires), fuel filter, air filter. Mile wise.

Mine is stumbling also, but not enough to notice unless you are really paying attention except, I have no problems accelerating both cold and warm. Kinda feels like a random misfire all across the board.

[Binjammin]

Most of those will throw check engine light codes/are not affected by the temp outside/engine.

The sensor I suggested cured my problems related to hot starts, 12621288158 is the part you need, $15 sensor, 10 minutes of labor.


Running too rich will throw code 1222: lambda sensor too rich. Its not always about the codes.

[M Quick]

Replace ENGINE TEMP SENSOR (12621288158) and make sure you are getting enough fuel pressure. Running worse as you heat up = too much
fuel.

+1 on that.

If that is faulty the car will think it's cold at all times and give fuel/air according to when it's cold and therefor run rich when getting hot.

[Binjammin]

You have either too much compression or too little. From the funky smell coming from the exhaust my guess would be too little. You may have a hole in your cat somewhere. also, could be that the intake isn't bringing in enough. I could be completely wrong though, and you may have too much compression (caused by a faulty O2 sensor, fused Cat, etc.) if that were the case, you may still get the smell, but you would usually get backfires, (assuming you were trying to accelerate quickly).

A funky smell can mean a lot of things, but low compression is usually not one of them.

Please explain to me how ANYTHING short of sucking in a ton of water can raise the compression ratio of an engine. :confused

OP it's likely nothing to do with your compression. Rings seal worst when cold, if you had bad rings leading to low compression you'd notice a ton of oil smoke and experience the worst symptoms when cold in the morning. It's not a ring sealing issue and very likely not a compression issue. A bad cat is possible, never heard of one weather related before though.


Stupid question OP.... when was the last time you checked your air filter?

[bsconz]

More info for you guys! I bought this car 6 weeks ago. At first it had a really bad fuel delivery problem that would cause it to almost stall and give the same symptoms during the afternoon. I was changing the fuel filter when I noticed the fuel coming out was like dirty poop toilet water and rusty brown. Inside the fuel tank was completely rusted out and I have no idea how the car ran with this crappy fuel. I changed the entire fuel system at that point. It has a new air filter too.


Today I drove it into work and it was about 85 degF out and it was fairly strong. Acceleration/power got a little weaker as the commute went on. When I leave today it will be about 100 degF and I expect the acceleration to be weak. The problem is intermittent though. It seems to happen when the car has been on for a long time or sitting idle for a while.

I measured the resistance of the ECT sbd IAT sensors and according to the Bentley service manual they are in spec. I unplugged the MAF sensor while the car was idling and the engine went nuts. Plugged it back in and it went back to a smooth idle.


Is there any way for me to check the o2 sensor and the cat?
I am more suspicious of these things or possibly the ecu.

I am also going to check fuel pressure, regulator operation, and compression tomorrow.

What is the weird looking sensor that boots to the back of the airbox and has 2 hoses going to it?

[bsconz]

What the hell is seafoam?

So far I changed the fuel tank, fuel pump, fuel filter, fuel pressure regulator, all o-rings, air filter, throttle body gaskets, intake manifold gaskets, spark plugs, cleaned the throttle body, cleaned the fuel lines, checked the iat, ect, TPS, & maf sensors, checked power to the coils, measured coil resistances, checked power to the injectors and measured their resistances, replaced the ccv hoses and checked that everthing was connected properly with no air leaks.


I don't know how to check the o2 sensor, check that the cat is good, check the ecu, or verify how much carbon buildup the cylinders have?


I can check the compression and fuel pressure next. Remember though, the engine light is not coming on and I would think that would narrow it down.


Another side note, when cleaning the thottle body out I noticed a fair amount of oil where the ccv hose connects. Could a faulty ccv system be causing this? Where is the ccv valve? Is it in that stupid little connector on the valve cover or inside the cover?

[somerandomdude]

Yes, it's the connector connecting to the valve cover.

Carbon build up will happen regardless the type or how old the fuel is. It's the nature of it.

[bsconz]

i just finished the compression test.

cylinder # - pressure (psi)
1 - 185
2 - 185
3 - 185
4 - 185
5 - 185
6 - 185

i'd say the compression is fine. bentley manual says the minimum compression should be 156psi.

i am going to lean towards O2 sensor or bad cats. i guess i'll have to take it to an exhaust/muffler shop. i can't really replace the exhaust in my driveway!

[elcoy]

Seaform is a brand name for a engine cleaner. It is the best it has saved me on snowmobiles mowers and cars. Avaiable at any auto supply center. Just follow the directions on can

[bsconz]

awesome, i keep hearing it mentioned here and there. elcoy, have you used it in your 535i?

i also just tested the O2 sensor. at idle before it warms up it outputs .42 volts. once warmed up the voltage fluctuates between .13 volts & .65 volts. when i unplug the vacuum hose to the fuel pressure regulator, the O2 sensor outputs a constant .02 volts. i think the O2 sensor is fine.

i think i've narrowed down the potential to something in the exhaust. i guess i'll take it to a shop.

[SMITTY525i1993]

Hey this is SMITTY525i1993. My car was running fine until the check engine light came on and my car wouldn't even do 5 miles per hour, idling rough, and hard starting. I got the codes read and they said it was a MAF, O2 sensor, and my injectors. I'm waiting on my new MAF sensor in the mail but I still can't figure out why it runs normal for a block or two and the check engine light comes on and the car comes to a crawl. I'm totally lost on this. Can anyone help me out with a solution.

Oother question from SMITTY525i1993. Where does the vacuum line from the fuel pressure regulator go to under the intake manifold go? I can't see the hook up. Without this vacuum line not connected will it cause my car to run like crap and have no power or acceleration?

[bigdawgfrommn]

if the car has up stream and downsteam o2 sensors pull them and do a pressure test on the cat, It should be very similar ahead of cat as to the outlet, if it is high you must replace the cat. If you don't have o2 sensor ahead and behind you can also drill 2 small holes that can easily be tack welded or even jb weld works. good luck

[7 heaven]

What did it turn out to be ?

[Binjammin]

Operator error, probably.

[mostafa20]

@bsconz (https://www.bimmerforums.com/forum/member.php?287693-bsconz)
i have the exact same problem. i tired all thing do. what did you do finally to fix your problem?