madman89

hello, i have a 1989 iroc z and the engine loses power at take off at when getting back into the gas from crusing. what happens is the car bucks and rpm's bounce up and down. will begin to regain some power when held to the floor for a couple seconds. any less then full throtle will do nothing or make a slight popping noise. fresh fuel filter a week ago. any help would be great, i just dont know where to go to next
thank you

8Mike9

Welcome to thirdgen.org!

Does the SES light flash? Have you pulled codes (if any) from the ECM yet?

Did this begin after you repleced the filter? Or were you replacing the filter to see if that was the issue?

Just a place to start.

madman89

no codes as of yet i changed the filter to see if it was the problem

8Mike9

Does it make a difference when cold or warm?

I/e first thing in the morning when you fire it up, does it run sluggish? Only only when the engine gets warmed up?

madman89

well it will do it at any time, now it also starts hard in the morning, i have to crank it about 3 times usually

8Mike9

Try unplugging the electrical connector on the underside of the MAF, see if it makes a difference.

madman89

i drove the car today 90 degree heat and very humid acted worse then ever maybe faulty mass air flow sensor? i havent unplugged it yet. when i do that and it runs the same would that be another sign of bad sensor?

madman89

ok well i drove it with sensor un plugged at first it acted like it was back to normal but then same problem and check engine light of course since sensor un plugged? what does this mean

8Mike9

Only thing I can think of off the top of my head that affects drivability like you mention in both open and closed loop operation, is the MAF and the ignition system.

Are you sure when the RPMs are jumping and the engine is bucking, the SES light is not flashing too?

You may want to take in your ICM and have it tested at AutoZone, etc. While you're in under the distributor cap, look at the PU Coil for corrosion on it, and the two-pin connector to the ICM.

madman89

made sure tonight ses light does not come on while bucking

Zap Racing

Do U have access to a scanner--even if U don't actually own one? From what limited experiance I have with computer cars, I would check the MAF sensor as well as the Throttle position sensor--after U make sure the Dist is working properly as written above.

madman89

i dont have access to a scanner since it runs different depending on the heat/ humidity should i just replace the maf sensor? also beacuse it didnt change when the maf sensor was unplugged?

Evil 88IROCZ

So much to check. I would start with a multi meter and hit the easy and overlooked points, 5v at the maf, make sure tps voltage is correct and is smooth from closed to WOT, hook up a fuel gauge tape it to your windsheild and see if the pressure drops when it loses power (maybe a dying fuel pump). Check plugs, wires (for burned or bad ohms, I had accel wires that went south out of no where and make my IROC seem like a 2.8) check dist. and ignition module. So under imediate load the engine bucks correct does it then smooth out and pull hard or normal to redline? If so it sounds like fuel but could also be ignition, hope my rambling helps good luck.

madman89

well when it does clear it will pull just like it should up to about 4000 rpm very smooth at higher rpms just on take off and getting back into the gas from crusing. now i have noticed on hot & humid days it is very bad and on cooler days it will run alot better. oh and thanks for all the input with your guys' help i am getting somewhere

rudyt5000

you might want to check all your vacuum hoses especially around that charcoal canister ...i found a bunch of loose vacuum hoses and it made a difference when i hooked them back up ....try cleanin your pcv valve or replacing it ....but i still have the same problem as you it sounds like i have a cam in it from what i been told ...but stumbles when i first press the gas but im still workin on it

Zap Racing

A lot of times, if U have any aftermarket performance stuff on your car, that stumble won't go away until U do a chip for it. I was fighting that problem for a long time--couldn't get it to go away no matter what I did. Got a budy of mine that is into chip tuning and it went away--IS MUCH BETTER NOW-- as well as running better in general and 3 tenths quicker at the strip!

Is your car stock or have performance stuff ?

C

madman89

yes, my car is completely stock

Zap Racing

Have U tried cleaning the throttle body and double checking the TPS as well as setting/checking the timing? U know the correct procedure for this--about the brown wire to disconnect by the AC blower motor, and usually have to do the paperclip in the socket below the dash, to put it in the diagnostic mode? May want to check and see if the timing plug (the one U disconnect) just to see if it hooked up at all!

I would HIGHLY suggest U post a question in whatever regional board that is appropiate for your location and see if somebody has a scanner that U can go over to their place and get him to hook it up and look at some data. Even better would be somebody that is into chip tuning--not to do a new chip--just to gather some data. Chip programmers usually have a computer program that gathers better data than the normal scanner!

black89ws6

Check fuel pressure, at idle, and during one of the stumbles. I had the same problem years ago, but with a v6. It turned out to be a fuel pump getting weak.

Quick_Trans_Am

iTrader: (2)

I just went through a situation similar to yours. Remove the MAF sensor and clean it. I used a toothbrush and a little dish soap, followed by a good rinse and time to dry out. If that wire on the MAF gets dirty, it can cause faulty readings in the ECM and cause a "bucking" or kicking when you hit the accelerator, and it tends to get worse when the ambient temp is hot and humid. Does the car feel like it wants to stall when you are coming to a stop? Give that a shot and see, the only thing you'll be out is an old toothbrush

Zap Racing

If that does "fix" it, then your MAF burn off is not working. Are U getting any codes? Code 36 I think it is for MAF burnoff relay--it's one of the 3 relays by the master cylindar on firewall.

C

madman89

well it does not set a check engine light.. ichecked fuel pressure yesterday and it read about 25-30lbs at idle didnt really go up any when reved up what should it be? i will remove the sensor and try that. any thing else i can use to clean it?

Zap Racing

If not mistaken, around 38 or more! Tha tcould be part of the problem, but I'm not the one to give the definative answer. Somebody more up on thirdgens needs to do that, but it could be the FP going out and under load (so to speak) it might be causing this problem or a big contribution to it!

By the way--fuel pumps are FUN to change on thirdgens--although there are ways to "flat rate it"!

black89ws6

It should be above 40, I believe. Also, when you take the pressure reading, the vacuum line that goes to the regulator should be disconnected. If it's hooked up, it will be reducing your fuel pressure at idle (good for engine operation, but bad for test reading).

madman89

i finally got the car running like it should . i replaced the fuel pump and now it runs great. it was a little bit of hassle to drop the tank but it was worth it.

strider681

I am having very similar problems and have replaced all ignition components. my fuel pressure reads 31 all the time. so do you have any specific tips for doing the pump yourself?? I am at my wits end and am prob going to attempt it.

madman89

first off mine was reading 30 psi all the time as well, just make sure all nuts and bolts are nicely lubricated before removing, you will deffinately need a hoist to do it, do you have a manual to go along with?

Zap Racing

If U are talking about replacing the pump in the gas tank, there is a way to flat rateit--replace it wothout dropping the tank. It involves cutting a hole in the floorboard above the tank--it has been done many times with descriptions and pictures posted here on this board.

Do a search about replacing the pump and read through the threads, until U find the correct ones.

When finished, U get a piece of sheet metal and screw it down over the hole , replace the carpet and no one except U will ever know!!!

strider681

well I considered cutting a hole in the back but decided it's best to actually take the tank out. but no I don't have acess to a lift or hoist or anything, just a jack and jackstands.. what do you need a hoist for?

madman89

you need a hoist because you need to lower the rear end down about 6 inches i just wouldnt want to do it any other way, and i deffinately wouldnt cut a hole in the floor just beacuse that seems like the hacking way to do it, i hve also heard of doing it that way

strider681

well can't you just take the rear axle out completely? how much clearance from the ground to the body did it need for the tank to come out?

madman89

well i had mine on a lift but you have to shift the tank a couple different ways to get it out. id say if u were on the ground youd need a few feet.

strider681

is it really necessary to "remove rear portion of the exaust" like the book says?? it doesn't look like it's in the way but if you have to kinda wiggle the tank out or whatever I can see how it would be a problem. the only manual I have to go on is chilton and it's vague. any hints, suggestions, etc is really appreciated. I am starting to remove my fuel tank to replace the pump and this is my first time so if anyone did it before, help please!! oh btw I am just using a jack and jackstands no lift or hoist so...

oh another ? do you need to compress the rear springs when removing the axle or just lower it and take them out?

madman89

first to get the springs out just lower axle for the exhaust, mine was all welded together so what i did was unhook it from the at conveter and move it back a little bit and swing it out through the passenger side wheel are(tire is off) and rest it on the 1/4 pannel

mjustdie

anyone ever think to check the egr? sometimes they stick a little, but not enough to trip the ses. happened to me already, sometimes removing it and cleaning fixes the problem, or you have to replace it. just a thought.

1MeanZ

iTrader: (9)

I just scanned the posts quickly and didnt see this. I think many of us a deep diving this issue way to deeply. My truck was doing this same thing and it was because the cap and rotor were bad. they were worn, which in turn caused the spark plugs to get dirty and accumulate deposits because they were not firing properly. 2 of my 8 plugs in my truck were almost completely bridged with deposits. I replaced the cap, rotor, and plugs and it runs like a new truck. If he does not have an SES light I doubt a sensor is reading out of spec. I chased this problem with my truck for about a week and figured it had to be something simple because the SES light never came on. YES MY TACH WAS BOUNCING UP AND DOWN AND MY ENGINE RAN HORRIBLE UNDER LOAD. ALL BECAUSE OF BAD CAP, ROTOR, AND PLUGS.

madman89

ok but fuel pressure is 30 psi and it should be at 45 in this case replacing the fuel pump would make it run like a brand new car

1MeanZ

iTrader: (9)

Yes, as I stated above I just quickly scanned the posts. My truck had the same symptoms as you car and replacing ignition components is what fixed it. I was only trying to help you and others with a similar problem. Can you tell me how a weak fuel pump would make your rpms "bounce up and down"?????? when my fuel pump went bad the motor just laid down and had no power, it did not "bounce up and down".

mjustdie

ignition problems would do it, my suburban suffered the same thing. unfortunately it started doing it again and it was the egr sticking. after a little while of running and being warmed up it would stop. as for the 30 psi for fuel, if you have the stock regulator, toss it, but it that will not make your rpms jump. never heard of gm sending any of the tpi's out with 45 psi stock. hell, check your coil. a bad coil will disrupt the firing of your engine creating spikes and drops in rpms.

madman89

well check any service manuals for a TPI 305 camaro and it will state 45psi fuel pressure. with a weak pump it will only pump what it can handle and that not being could causing the sugres. its amazing what the correct fuel pressure can do. also your suburbon isnt tpi so it would be less pressure.

mjustdie

1. 45 psi! I've been playing with tpi for 5 years, playing with 3rd gens for 9, never have iI seen a tpi hit that amount of pressure without an aftermarket regulator. Especially a 305tpi. If you ever purchase an aftermarket regulator, it will tell you to run the fuel around 45, and the manufacture will claim a hp and torque boost due to better atomization. I actually had the same problem last year with my IROC. It was both EGR and fuel pressure. It started when i added ram air. It created a lean burn and tripped ses and also disrupted the intake manifold pressure after long hard runs on the highway. After playing with the pressure I stuck it out at 48 psi and I actually just played with the EGR to loosen it up and never had the problem again.
2. my suburban does run less fuel press., i'm not a moron. it's the same concept. i'm just trying to help, it's a problem i've seen misdiagnosed all too often.

Instead of spending all the money on pump maybe check the simple things. Throwing out for a new EGR gasket and removing the EGR and cleaning is better than $150 on a pump, also better than almost $100 for a regulator. It's your money and your time, best of luck and keep us posted to what the problem is. I'm just trying to help.

madman89

well im just telling you what my expeirences were, not trying to say hey i know so much because thats far from it we all can learn from each other. but in my manual i ahve which is a chilton it says for my 305 tpi pressure should be around 45.

mjustdie

it should be, that's for sure. but chiltons and haynes aren't always accurate. i personally almost smoked an engine because of a haynes manual. if you look around the site you will see that our tpi's weren't exactly given all they could get by gm. another thing, are you checking your f/p with the vac line on or off?