Hesitation under power

[hotrodwolf]

So i fixed the evap system on my car (gas cap) and the engine light is no longer on. The car still has a hesitation. Mainly going a constant speed, or if the cruise is on, and i come up to an incline. The car stutters and shakes. It only goes away if i put the pedal down enough to downshift. Also if i get on the gas, it will stutter. I have new fuel pump and filter. I've swapped old and new one in. rail pressure is at 59. any ideas?

[comanche]

How many miles on the car?
Do you have available a scan tool with a live data feature?

[Valley olds]

I don't know about the alero, but I do know my delta would have some stutters and shakes when its spark plugs were bad. Also, maybe the spark plug cables could do that too. As stated though, I don't know if this applies to the Alero.

[hotrodwolf]

My uncles scan tool has live feed on it. What should i be looking for? He doesn't know how to read the live feed, he just gets proms from it. I was thinking maybe spark plugs. The car has 168000 on it.

[AlbinoMonkeyRat]

plugs may be right...though how old is the cat? if it's clogged (or restricted) you could have too much back pressure and it could slow things right down.

[hotrodwolf]

brand new cat about 4k ago. i'll try plugs, but now my p0440 and p0442 engine codes are back. I'm gonna have to get the evap system smoked to find this leak i think. I've replaced the cap, new tubes under the hood and back at the tank. I just cant find a leak!!! grrr:banghead:

[clutch1]

Plugs are a good start, and so is checking max voltage you're getting from the coils.

If the injectors have never had a thorough cleaning (not just pouring BS into the tank) that's also something worth doing, especially with that many miles.

Unless your new pump or cat failed, which are unlikely.

[hotrodwolf]

New info on this problem.
So i got the car to throw a misfire 0300 code. Its been cleared and i put in new plugs. The old plugs were actuall wrong from the previous owner. They put in 3.3 or 3.8 cheap plugs. anyway, the problem didn't resolve.

Here's the weird thing now. There is still lots of miss fires under power. mainly when speed is the same, but going up hill to maintain it. Now as it misses, the service engine soon light flashes until i'm done with the hill, then turns off and stays off. Anyone know what that could mean?

[clutch1]

Flashing SES light for misfire means you're misfiring much worse than a nonflashing SES light for misfire... it's to the point where its dumping raw fuel down exhaust and melting the cat (assuming it's getting proper fuel, of course).

First things first. You have a live scan tool. Good.

Plug it in, take it out on the road and watch it in various situations. Cruising, no misfires, what's the numbers? Stomp on it for a bout 10 seconds, what's the numbers? Drive up a hill and make it misfire badly, what's the numbers? That'll help.

Next up. When you did the pump, did you do a fuel filter??
If not.. DO IT NOW NO QUESTIONS ASKED.
Putting a new pump on an old filter.. kiss that new pump goodbye pretty damn soon. Old filter's so restricted you'll overheat the new pump.
New filter, then check fuel pressure AND volume at idle... should do 15 ounces in 15 seconds when ya press the button.

Check the spark voltage you're getting.. make sure the coils are strong enough to make a good spark. ONE very weak could could be causing the problem, absolutely it's a good possibility.

If fuel pressures and spark voltages check out OK, get a legit injector cleaning, see if it clears up. If nothing else your injectors will atomize MUCH better and you'll get better fuel economy.

Now, go test, tell us what you get and we can fix it.

[hotrodwolf]

I did the filter of course. and i'll get at it asap. I have allready tested the resistance to the injectors and all are good. I'm thinking coils as well now. random misfires.

[comanche]

Well, let's see if we can isolate this to one or two cylinders.

Does your scan tool have a "misfire counter"?
Some scan tools have this... it's a screen you can access that shows all cylinders and counts the number of misfires for each individual cylinder.... live.

It sounds like one of the coils might not be putting out enough voltage under load... or it is shorting to ground.
Or... one of your injectors has issues... but I think that would be less likely in this situation.. it would probably misfire all the time then, not just under load.

I'd try to figure out which cylinder is causing the misfire.... I'd make that my priority 1.

An ignition scope test would be excellent for this situation... do you have an oscilloscope available?

[clutch1]

Well, let's see if we can isolate this to one or two cylinders.

Does your scan tool have a "misfire counter"?
Some scan tools have this... it's a screen you can access that shows all cylinders and counts the number of misfires for each individual cylinder.... live.


I'd try to figure out which cylinder is causing the misfire.... I'd make that my priority 1.



This. TechII and Genisys IIRC have the misfire live data for each cyl. Super helpful.

[[ion] C2]

I also received a P0300. Pull the plugs. Sometimes one will look cool:

http://ion-productions.com/brokenPlug/small002.jpg
http://ion-productions.com/brokenPlug/small001.jpg

My fuel injectors are at Kinsler being examined to make sure that one has issues (I hope like hell it is), then all will be cleaned and flowtested.

[hotrodwolf]

^^nice!^^^ i checked the plugs. they are new. I'm only getting random misfires for now. My scan tool isn't isolating just one. I have a new coil pack with lower sensor on the way for it.

[hotrodwolf]

Just an update. The coils and icm didn't fix the problem. Now i think i'll check the injectors probably. What resistance should they read? And are there better injectors to get if i must replace them?