I gotta '90 IROC with the 350. bout a year ago i noticed some surging, mild but still there. it was really noticeable when you let outta the throttle and picked it back up again, say like going down a hill. well its progressively gotten worse. its gotten so bad its loading up running really rich and my gas mileage is down to around 8 or 9 miles per gallon. i can romp on it and man the unburned gas would chock you to death. but it runs better on top end then anywhere. if your cruising at 45-50 its constantly surging, almost like the ignition is being turned off and on. im beginning to think its the computer or the gas regulator but really i have no idea. i have changed the plugs, plug wires, the distributor cap and rotor, the coil, the map sensor, the O2 sensor, the TPS, the IAC, the water temp sensor and gas filter, and still no relief. im at my wits end here. anyone else have this issue or have any idea what to do next.

 

It sounds like your having almost the same problem as I am. I would check to see what codes it is running. I think I might take mine to autozone today because I have heard they do trouble shooting inspections. You should give that a try.

 

I have tried to get the codes. the mechanic says its not communicating with the diagnostic meter. come on guys...what yawl think here? im at wits end with this thing.

 

You check the fuel pressure?

If all of your grounds and whatnot are good and you still can't get the ECM to communicate if could easily be slowly failing.

 

No i havent checked the gas pressure can someone chime in and let me know whats normal?

 

If i remember right I beleive its something like 40 psi.

 

My 92 gta did alot of the same things. the surging and also running rich, What I found was 4 fuel injectors went bad and the good ones tried to compensate for them. After awhile it caused my computer to fail. When the computer failed it ran alot like yours .So I would at least check the resistance of your injectors to make sure they are OK, (beter safe than sorry)

 

what should the resistance read? also there is one other sensor mounted on the back/underneat side of the plenum near the gas pressure regulator. what is this sensor and can it cause these symptoms too?

 

BTTT

help......please!

 

ok this is the sensor i was asking about...what is it, whats it do? it has the brass nut on it..........

 

I think that is a intake manifold temp switch, only about 80% sure though. As far as the injectors in think the range is around 11.5-14. But anything under 11.5 is bad .

 

thanks for the input... does anyone know if that can cause my issues????

 

I checked my Fuel Injectors yesterday. most read above 12 ohms i did have one that read 6 ohms. does this mean its bad???? can this one injector cause these problems????

 

well regardless you are on the right track any time surging is an issue it's a fuel delivery issue. Temp can affect resistance get the motor hot, and check if you haven't already along with cold. If one injector is drastically different then all the others probably a good sign it needs replacing, but before you go through that have you changed fuel filter lately? Yes one injector can cause the problem

~Couch

 

Thanks for the info......
can anyone tell me what that sensor is in the picture above? and what does it do????

 

Anyone??? the sensor in the pics....wth is it? what does it do?

 

oh still... you need a haynes manual man Ill try to figure it out

~Couch

 

no never mind dont have info on TPI, if nothing else you can go to your local auto parts store, and look at pictures, and have them bring you stuff until you find something that looks like that.

~Couch

 

The sensor in the photos is the manifold air temperature sensor.

 

many things can cause that... tps should be set at a starting point of.48-5.4 min. thet fuel pressure should be set at40-47 psi...and will hold for atleast an hour if not injectors leaking or a bad fuel pressure regulator is to blame..... clean the iac sensor. set timing at a base 6.. injectors should be at least 11.5 and up.... mine on my 88 gta 5.7l tpi are 180.4... ignition coil? might be... coil pick up? maybe... if no codes you have to check everything...mine was a code 22 and 33 and 34... they point to the maf and the tps....what it turned out to be was a dirty throttle body, vacuum leak, bad throttle body gasket and horrible iac... oh by the way the tps sensor was way out to... i did my repair one thing at a time testing everything along the way and found lots of stuff wrong!!!! it's an old car and they all need work and you are never done.. just don't go blaming one part because the computer says it may have a fault! computer problems do happen but not likely...

 

thanks for that info. i have changed every sensor except the MAF. ive changed the TPS, IAC, O2, Water Temp, Manifold Air Temp, MAP, coil, plug wires, distributor and rotor button, plugs, and fuel filter. Where is the MAF? Thats the Mass Air FLow correct??? I cant find the damn thing.

 

You see that black thing in the pic labeled Bosch. Thats the MAF.

 

yes

~Couch

 

Ok gotta update I changed what I thought was the bad injector an the manifold temp sensor. I think it helped some. Now I've determined that I'm gettin bout 9 miles to the gallon. Its runnin rich as hell. It hasta be a fuel injector stuck open or a fuel press reg Right? How can I tell which injector is stuck open? Read plugs??? How? What's yawls opinon on this am I on the right track?

 

glossy black plugs mean rich, they should be tan-brown for normal operation. fuel pressure regulator leaking would show high fuel pressure, there are places that test fuel injectors for flow. Yes you are on the right track.

~Couch

 

I am also at my wits end with my '91 Z28, I replaced everything you did plus the fuel pump, with no improvement. Only things left are the regulator and injectors. I did notice an improvement in the way it idles if i unplug one injector while its running and it doesn't matter which one, so I'm leaning towards the injectors. Someone out there has had this problem and has fixed it. Come on Camaro Brothers help us out.

 

A fuel pressure regulator failure wont necessarily cause high fuel pressure. The diaphram can rupture allowing fuel to be siphoned through tre vacuum line to the plenum. If the hole's large enough, fuel pressure will look about normal. Pull the hose at the plenum and look for fuel to be shooting from it.

While I would bet that your problem is your injectors, it would be good to check your O2 sensor as well. A shorted O2 sensor will cause fuel correction to go high, causing a severe rich condition.

 

OK gotta update.....ITS FIXXED!!! after $600 inparts i finally fixxed it with a damn piece of .50 cent tape. I got so pissed that i went back and reexamined everything i had done, checking that all the sensors were plugged in good and really looking at the wire to each sensor. well the O2 sensor wiring runs in a loom with the temp sensor. it exits the loom and runs unprotected for several inches and its routed to the front of the motor by the motor mount. i moved the wire back and looked real close and sure enough the damn wire was bare and had been shorting out against the frame. i removed the wire and rerouted it and repaired it. plugged it all back in and damn! it runs great with all the new parts in it. lol so if you have a car running really really rich i can tell you first hand a shorted O2 sensor will do that. heres a pic of the wire...kinda blurry but you can see the copper exposed. thanks for all the help. i hope this helps someone havin the same problems as me.