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PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! ok...heres my list of problems...just gonna start by sayin i dont know much history on car as i just bought it 3 weeks ago...has 305 tpi setup ...last owner says has ne map,tps,distributor,and iac...i believe him they look new at least...heres the issues, car sometimes has a weird rolling idle(form about 500-1000 rpms) , when in gear and under no specific donditions (does it when braking decelleration or reverse gears) she stalls on me...starts back up idles fine...next is todaay while driving (unsure exactly how fast i has going ) i lost power when i opened her up stayed running but had no power when i hit the gas...i am stumped please PLEASE i need useful info becuase my mechanic says i need a new engine and quoted me 3grand for an new one(hes a d-bag cuz if it needed a new motor id drop a carbed 327 in for about 500$ myself but i want the fuel economy of tpi) anyway if you can help me solve any of these issues i would greatly appreciate it i love this site!!!!!! |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! id start with a careful tune up,then do a codes check.look at your throttle body,it cant be dirty and still work so clean it also hows your idle air control valve? is it all carboned up?is your throttle position switch adjusted correctly?these things have a effect on idle.i hope this helps,and good luck |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!!
Originally Posted by david chambers
(Post 4867004)
id start with a careful tune up,then do a codes check.look at your throttle body,it cant be dirty and still work so clean it also hows your idle air control valve? is it all carboned up?is your throttle position switch adjusted correctly?these things have a effect on idle.i hope this helps,and good luck |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! are you getting a Check Engine light? Grab a paper clip, go out to the car, under your dash on the drivers side, us will see the aldl i think its called, if im wrong plz correct, bend the paper clip into a U and insert it into the top right two holes "should be like 8 on top and a second row of 8 Turn your key on, but dont go as far to start the motor the check engine should blink, blink blink, log pause and do this twice then go into code mode, search how to check the codes, this is insite what to narrow down. Let us know what ya find |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! The surging idle is almost always caused by lean fuel mixture. Lack of fuel would also explain your power loss. Would be helpful to see data when this problem is occuring. Also, running the engine lean will quickly destroy it. If the PO ran it with a fuel supply issue and especially if he tried to rod on it, the motor may be toast. Compression and leak down tests should verify this. One other cause for this set of symptoms is ignition. Carefully inspect the distributor, wiring, coil and plug wires. Look for heavy rust in the dist, along with damage or looseness in the pole piece and timing core. |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! i ran the codes and got 45...rich mixture...ive kinda cme up with a few ideas upon further invesegation 1.maybe coolant temp sensor (fans dont kick but when jumped they work perfectly i will replace that...2.bad o2 sensors (old ones have been spliced in? i thought wtf why would someone do this lzy jerk!) so ill replace them as well im almost 100% positive its not a fuel pump bad bc i can hear it pressure up when i start car...and i will check fuel pressure and maybe if i can find a parts store that has it reasonably priced get a pressure regulator and clean out my egr...when i pulled the throttle body to clean it there was a sh!t ton of carbon in the intake so i will disassemble intake and have themm hot tanked and cleaned(it has to come apart to get to egr anyway) any thoughts/comments on this?am i taking proper steps or will this all be a waste of time? im no expert on these cars but id love to see this one returned to its former glory! |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! Do the plugs look dark like they've been running rich? Spliced O2 sensors are never good. If one or both O2s are reading false rich, they will force the system lean, trying to bring O2 sensor voltage back in line. You can tell this by plugs that are obviously lean, even though the system thinks it's rich. A scan tool would be great right now to check BLM and Integrator(long and short term fuel trims). |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! havent pulled the plugs yet but i will be this thursday or friday as i am gettin all 8 new ones,as well as getting my hands on a multi meter to test 1.)vss connection(no speedo reading) 2.) cts (fans dont kick unless jumped) 3.) TPS (previous owner replaced so may need to be adjusted) and will also replace o2 sensors with new pigtails etc old wires have been spliced which i no good maybe the cause ... it is a far off chance but it could be defective o2 wiring that is sending improper signal to ecm which makes it kind of "choke" when warm and i accelerate? <---- is that a possibility? |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! BUMP |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! I don't trust the ground for the o2 sensor. It has to go through the o2 bung, into the pipe, through the manifold, then the head, then the block, and finally a ground strap, not to mention the questionable wiring splice. You may want to consider upgrading to a heated o2 sensor. The benefit is a dedicated ground wire from the sensor and a built-in heater. I was doing alot of driveway tuning and my single wire o2 sensor never warmed up properly. This caused alot of added heartache. Then I put in a heated LT1 4-wire o2 sensor and now my o2 voltage behaves exactly as it should (lots of crosscounts). Did you get a chance to check the fuel pressure yet? It should be ~42-47 psi when not idling. Leave the gauge attached and stop the engine and note how quickly the fuel pressure drops. If it doesn't hold pressure then your injectors may be leaking. edit...I have been informed that the fuel rail should hold pressure for at least 20 seconds. Oh yea...I also had to replace all my injectors because 4 of the original 8 were literally dripping fuel into the runners. It ran this way for years but not well and this rich condition covered everything with carbon...sounds familiar. |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!! I don't have access to diagrams for the 91 here at home, could certainly find them on this site smowhere, but I believe they had heated O2 sensors by that time. I also believe they had seperated banks into B1 and B2 with a sensor for each bank. If I understand the OP correctly, someone spliced the pigtails from the original sensors onto new sensors that had the wrong connectors. I've seen it too many times. As for the OP's question, a fuel management system which is forced rich or lean by defective O2 sensors will run very poorly. The engine is either flooded with or starved for fuel. Block Learn can alter fuel delivery by as much as 25% to correct for problems in the engine or fuel delivery system. If it falsely richens mixture by 25% on an otherwise healthy engine......... you get the point. |
Re: PLEASE HELP ME WITH MY 1991 Z28 AUTO 305TPI!!
Originally Posted by ASE doc
(Post 4872111)
I don't have access to diagrams for the 91 here at home, could certainly find them on this site smowhere, but I believe they had heated O2 sensors by that time. I also believe they had seperated banks into B1 and B2 with a sensor for each bank. If I understand the OP correctly, someone spliced the pigtails from the original sensors onto new sensors that had the wrong connectors. I've seen it too many times. As for the OP's question, a fuel management system which is forced rich or lean by defective O2 sensors will run very poorly. The engine is either flooded with or starved for fuel. Block Learn can alter fuel delivery by as much as 25% to correct for problems in the engine or fuel delivery system. If it falsely richens mixture by 25% on an otherwise healthy engine......... you get the point. |
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