My 89 IROC-Z has about 38,500 original miles on it. It has started giving me a problem. Here is what is happening. About a month ago, I was driving down the highway and I noticed when I pressed the accelerator it did not have much power....It was almost like it was starving for gas. I got to my destination parked it and several hours later I got back into it and drive it back home. It gave me no problems at all. The car stays stored and I only drive it sometimes on the weekends. About 2 weeks later I took the car for a drive and noticed that it had a minor miss but for the most part drove great.

I fueled up cleaned up the car and parked it. I purchased some STP Fuel system treatment. I parked the car for about a week.

Last weekend I took it for a drive in the morning and it started missing bad, it got regressively worse to where it would not even run. It got to the point where it was real rough when I was trying to start it up.

It finally got to the point where it would not start. I let it sit for about 2-3 hours. I went back and started up the car with no problems. I let it sit and run for about 20-30 minutes with not but a small miss.

The next day I started up the car with no problems and drove it for about 30 minutes. I parked the car and this weekend brought it out. I have drove it and it is giving me no problems. I am somewhat "perplexed" over this issue. I thought at first it was bad fuel, or gas line filter or fuel pump. Then I have thought it was something with a sensor or something. Help !!

Thanks,

 

I too am having a similar problem. though a little diffrent. i have what feels like some one holding back the vehicle slightly, kinda like someone taping the brakes. So i get tossed back and forth slightly, enough to be annoying and i can hear a slight miss in the exhaust. yet when i get on it above 2000 rpm it runs fine from what i can tell. after talking with a few guys, i've determined that its fuel related. I have put a gauge on my fuel rail and noticed that at idle and up to a certain rpm (wasnt able to look at the tach) the fuel psi flutters rapidly from 30-50 psi and eventully it settles to about 42 psi and climbs like normal. I just upgraded the cam and set the psi to about 50(not running) about 45(running without vac). im wondering if i too have dirt in the injectors/weak ones/ or a bad regulator.
thanks for any info.

 

Any SES lights? IF it flashes when it's happening it's a missfire. You guys have MAF sensors? In my old '85 T/A, performance sucked and it chugged when the maf went out. Have you changed the fuel filter lately?

 

Really could be alot by that description. I'd check the basics (cheap stuff). Check connectors (MAF, relays), change the fuel filter ($6 and a half hour are all you need), test resistance of injectors, etc.

 

How is the fuel preasure ?

 

well my problem started when i replaced the coil that was mounted on the firewall with the proper bracket on the motor. i replaced the cap and rotor at that time. once this condition appeared, i did a set of NGK vpower plugs and wires. seemed to get better for about half a day then back. i then broke down and decided that i would just start over and while doing so i would install my new cam and slp runners.(new fuel filter also) got it together and at first it was perfect. but over driving it for about 2 days it slowly came back. its not as bad now but i can still hear and feel it. in figuring it was a fuel problem was when i learned of the fuel psi flutter at lower rpms. what should the inj resistance be for an 89? they look to be the multec style injectors, if that matters. no ses light or anything to signify that the computer is seeing a problem with it. also my data line is not hooked up so i can hook a scanner up to see if i can see anything in the data stream from the ecm.
my fuel pressure seems ok none running and at higher rpms but will flutter from 30-50 rapidly at idle and eventully will settle to about 42ish and then climb higher

 

somewhere around 14 ohms is okay for the injectors. The flutering at idle is wierd. Things I can think of for that are. IAC , CTS sensor , I am sure there is more .

How are the plug wires ? You changed everything but them I see. Also I would go back to the origonal Delco plug.

 

i normally am for all factory parts.. but they were cheaper and i wasnt tryin to spend alot of money(real tight right now). i knew ngk are good plugs so i figured they cant hurt being a v power plug. they have to be better then the autolite platium crap that was in there.

 

With that low of miles I'll assume you keep it stored alot. One thing to check for is rust in the tank. If the tank isn't full when you store it, rust builds up. The rust flakes will then get knocked off when you fill the tank or drive it. All the rust will settle to the bottom until you drive it. When you do drive, it will churn the gas up making the particles suspend in the gas. While driving, the flakes collect on the fuel pump screen. This will make the car starve for gas and make the pressure flutter while the pump is trying to pull gas through the rust. Let it sit for a while, and all the rust will fall off the screen, and the car will act normal until you churn it up again.

 

MULTpi im have the same exact problem as u...when im driving at around 1500-2000 rpms the car feels like its bouncing back and forth a little from the rpm's jumping but only when crusing. when i cruse below or above that its fine and when im riping on it it is fine. it is bugging the heck out of me. also when the car is idling in park and i give it a quick rev it bogs down and hesitates for a second then it revs up. My car was sitting for about 9 months because it got in an accident (friend took the car and crashed it) for the first couple of days after i got it back the car felt like it wasnt doing it but then once i got it on the road and drove it more it started to do it again i changed the plugs and cleaned everything up but nothing worked so far

 

i had a very similar problem with my car. installed a new cap and rotor, new plugs, new wires, new o2 sensor, cut off the cat (cheapo 3 inch magnaflow cat thought it was clogged), new map sensor, new coil, new fuel filter, new fuel pump (walbro 255lph) as went in. then i got smart and started testing things. turns out my number 5 injector didnt have enough resistance.

its suppoed to be between 12-18ohm with 16 being normal. all mine were fine in the 16.0-16.5 ohm range except number 5. it was 5.1 ohms. do yourself a favor and check your injectors if they arent new. if you dont have a volt meter, do what i did and pick up one from craftsman. i got mine for 25 bucks normal price at Sears and i KNOW ill use it later as well.

 

after talking with a friend from another board. he described my exact problem, only his sisters car and brother inlaws truck were both doing it.. did the normal tuneup deal to no avail.. ended up doing a good fuel system cleaner. the pressurized can deal that hooks to the fuel rail.. cleared it right up. i messed something up on mine and it wont run now, working on fixing that and then im going to start testing the inj to see if i have any bad ones. got a buddy thats got some 24# for sale. so i might upgrade to them if i need to. im just curious on that regulator flutter at low rpm.. i know from playing with my 2.8 that it should be sold. is it possible that the reg is bad since when i went to adjust it up to 50# there is a fine line between getting it to 50 and hardly even a 1/4 turn and it would peg it beyond 80.. i could hear the pump struggline and it would sit there and bounce the needle on the gauge. or could it be possible that with a bad inj not working properly that it could be causing the flutter.

what adj reg are you guys running? i have the crane one thats takes a 1/4 allen, which is a pain to adjust with the plenum on. i have the holley with the large **** on top. i was wondering if there was anyone running that one and if there was enough room to use it.

 

Hey man..How are you?..Thanks for the heads up! I never thought it could be rust in the tank. Someone else also thought it could be an injector acting up. I am curious about how I would be able to find out if its rust in the tank without dropping the exhaust and tank. Any ideas? I drove the car today and it drove just fine! It only missed a little while while I had it out out on the Highway. I hate to start replacing things only to find out that its rust in the tank or a filter and on the other hand I don't want to drop the tank and find out that thats not the problem.

Thanks,

 

Unfortunatly you have to look in the tank to see if it's rust. I can't think of any way around it except trying to capture some gas before the filter and seeing if it has small particles in it.

 

What would happen if you let the air out of the bleeder valve by the fuel rail?

 

i guess you could remove your fuel filter and stick a pan under the car and just turn the key to run. that might do it but it will more than likely be very messy. but if you are getting rust somehow past the filter and to the injectors, you should be able to see it in a clean container using my idea..

 

Rust will emulsify with gas and water, then dry up leaving the rust in a solid powder form, clogging the fuel system over time. The fuel filter and pump sock will not filter out an emulsion.
Don't leave the tank full when in storage, or use a fuel stabilizer (gas drier) and let it run for a few minutes to circulate the additive through the system before storage.
FYI
I never put gas immediately after a tanker has unloaded, that stirs up what is called the bottoms which you don't want. I always ask when the gas was delivered. Cheap gas will destabilize faster than quality fuel, when it breaks down it oxidizes and creates sludge.

Assuming none of the above applies:
A larger cam will usually require a higher idle. Even if it's a MAF engine, minimum air should be set with the advance disabled to were it idles without stalling, or dying, and tune the ECM accordingly (i.e...change idle rpm..etc.)

 

After many different tests and thinking I had a problem with the fuel system, it turned out to be nothing with the fuel at all. I changed the fuel filter and was still getting about 58-61 pounds of fuel pressure on the fuel rail. I took it to the shop and run the system scan on it. It showed no errors at all when it was running fine or when it was running rough.

It turns out that the problem was with the pick-up coil, distributor and ignition module. They were corroded I suppose from moisture build up over time and it had started to rust. The car would run fine sometimes but once you got it out on the road it sometimes would loose power and eventually die. The pick-up coil was corroded. This was replaced and 650.00 later it is running fine.

The shop mechnic told me that it was because the car had been sitting up. It only has about 38.000 original miles on it and over time it had just built up some corrosion.

The car is running like new!!

Thanks,

Eric

 

maybe thats why my problems started when i took the dist out. to bolt on the coil bracket. it didnt look real bad under there but i guess i could have disturbed something. have to pull the cap off and take another look that pickup coil. id been suspecting the module for a while now.

 

ok, little update on this one.
so i tear into the dist to see if i have a prob there, find that the conn is duct taped up, so i end up replacing the whole dist since the roll pin refused to come out. runs good for about 10 min and then it comes back. then after a few weeks of driving it i start to feel like its getting worse, little stronger feeling of it kicking back and forth. but i was coming home from school and it got bad. i could hear a "hollow" sound in the exhaust. just didnt sound right. and it droped the idle down to about 750 and started shaking. no up until now, it never really shoke, just the feeling of it moving me around from 1200-2500 rpm. i've had it parked since then and havent touched it to see what is going on. i did ohm out the inj and got about 16.2-16.8 with one being 17. it still has lots of power. my next plan is to pull the plugs and see what they look like. anyone have any ideas on what else to look at? everything else in the ignition are new.