hello i have a 1991 pontiac firebird formula and i just rebuilt everything on it but sometimes it wont idle and sometimes it does, here`s whats in it------------ 5.7L,mild ported 083 heads with 2.02-1.60 valves, LT4 hotcam, 58mm throttle body mild ported stock intake, headers with dual cats and flowmaster exhaust, 24lb ford injectors, 700r4 with 1900-2100 stall and stage 2 shiftkit, 4:10 gears, and a custom chip. if i forgot anything else important let me know. I realy need help this thing is crazy, Ok so when i try too start it at a cold start the first time it did everything it was suppose to do and warmed up and didnt die on me. then when i tried to turn it off and start it again the idle went up to like 1800 then drasticaly dropped to like 700 and reved up and down a couple times and died. It does it alll the time back and forth, i forgot to mention the code 43? not sure why thats showing? Could anyone please help me with this, im in the procese of breaking the motor in but i cant get it too even run right?

 

EGR valve

 

ive checked the vacum on the egr and it was good

 

The valve itself or the solenoid may be bad. Deactivate the whole thing and plug off the vac source and see what it does.

 

how do i deactivate it?

 

i moved the timmin earlier to get it kinda where i thought it should be but it idled up and down from 1000rmp`s to 800rmp`s like a vacum leak in park, but in drive it idled smooth at 700rpm im not sure if this is normal??? could someone please tell me, and also not sure where too set the idle or fuel pressure???????Also still showing code 43????????

 

if there is anyone with any info about the lt4hotcam and why it isn`t running right please let me know asap ty.

 

code 43 is knock sensor, did you set IAC and TPS on throtle body?

 

i just changed the knock sensor and the check engine code cleared, but it still runs really bad, hardly drivable. I have tried to set the iac but i dont know if i did it right, heres how i did it----- jumped a and b under the dash, then turned the key too the on position, the waited 45 seconds and unpluged the sensor and with a and b still jumped (not sure if im suppose to leave it jumped while i set the screw) i started the motor, then i tried too adjust the idle as low as posible but with this cam i was only able too get it to idle at around 650 to 700 but idled like crap, im not sure how much rpm`s would be too low for this cam? As for the tps its not adjustable so if i check it and its not right even though its brand new what should i do?

 

i was just reading about a couple of other threads with people having the same symptoms and it ended up being the ecm, any opinion`s would be really helpful.

 

TPS is adjustable.

https://www.thirdgen.org/tpimod2

Also who did the chip for the combo? You have changed a lot to that engine and if something on that chip was not set correctly you could be having problems like this.

 

the brand new tps i bought is preset and isn`t adjustable, the holes are pre drilled to fit and not move. should i but one for and older model so that i can adjust it?

 

Newer GM TPS' are non adjustable. The ECU recalibrates everytime the key is cycled so it's not needed.

Just dont put your foot on the gas while inserting and turning the key or it'll be mis-calibrated for that ignition cycle.

If you put a late style non adjustable TPS on a system originaly equipped with an adjustable one then this could likely be part of your problem.

I have the adjustable TPS (on a TPIS 52MM TB I got cheap) on my originaly non adjustable system and it seems happy enough.

 

Hmm preset TPS. Havent heard that one yet. Learn something new everyday. What i would do is hop over to a junkyard and yank one off a junkyard TPI motor. I wouldn't buy a factory one new just to have the same problem. But having an adjustable TPS will at least eliminate that as one of the possible problems.

Come to think of it you can check the TPS you have now using the link i gave earlier to see what the voltage is set at. Something tells me since there is no adjustment its not quite right.

 

ok cool thank`s guys for the quick response, ill check the setting on the non adjustble one thats on there now and let you guys know what it is in about a hour or less. If it is not preset right there are no f-body`s here in cali where i live so where else would i be able to find an adjustable one?

 

Most EFI GM's for several decades used the very same TPS. If you have a friend or family member with a GM thats more than 15 years old it just might have what you need to do a quick test.

 

are they the same on a 1992 2.8L camaro?

 

It might be, I dont know all the various aplications of adjustable and non adjustable TPS' but iirc the fixed type came out on the 85 2.5L iron duke motors in Fieros and F bodies and were introduced to more and more cars from that point on. I know my 1990 TA came with the non adjustable kind.

If you can just pop the hoods on a bunch of older GM's until you see one with the slotted holes and the same style connector, even if the part number is different it should fit and work the same.

 

ok cool ty for the info, im gonna check the volts on the one thats in my car right now and post the results in a few

 

ok the tps checked ok is was at 0.9 at idle went up to 4.7 at WOT then smoothly back down to 0.9 what would be next? I was thinking about going to the wrecking yard and pulling and old ecm to replace my 7730 and see if that helps but im not sure which vehicals would have this ecm? anyone know ?

 

i also checked the ohms on the fuel injectors they mere all 14.8, im not sure if thats good for the 24lb ford injectors or not?

 

TPS sounds off to me volts should be .660vdc - .760vdc for speed density



http://www.golenengineservice.com/html/tps.html or

http://www.iroczone.com/2009/10/adju...on-sensor-tps/

 

I saw the exact same symptoms on another TPI. It was a cross between the harness connectors being switched on the knock sensor and fan switch. Also, the gaskets between the runners, plenum, and manifold were messed up during re-assembly.

Just a thought.......

 

well i checked the wires and there on correctly. My aldl cable came in yesterday and here are some of the readings it gave me but i dont know what they mean http://216.252.121.32

 

any codes after knock sensor change?

 

it took care of the check engine light but my car still wont run unless the car goes into closed loop mode, any idea why it would be doing that?

 

once had and idle problem on 3.1 , I put egr on backwards? check for vacum leaks around intake and tubes with spray, Is it just an idle problem or all rpms?

 

ive went threw two cans of carb cleaner and no change in the rpms at all, and when its in open lopp it wont run or idle good at any rpms it just misses and sputters like some plug wires are off then kicks into closed loop and wants too idle ok.

 

Sounds like you need a tune. And block off the egr with a block off plate. Mail order tunes are not going to cut it. Every engine is different, especially when you change things like the cam, injectors,....etc. You need someone to personally, datalog, and tune with a wide band. That is the only way I will tune one.

 

the guy who did my tune said that even with the stock prom it shouldn`t be giving me this much probllems. he had be buy the ALDL and run a scan and see if it was in the tune but has not got back to me yet. will the tune be efficient this way?

 

do you notice a change in timing when it goes from open to closed loop now that you have it hooked up to laptop.

 

i could check that in a few and let you guys know, but i need the software too open it too look so im downloading it now.

 

here`s what the guy who is tunning my car emailed me about it just now, does this sound right? ok, chip is set for 24lb injectors so I think we are ok there but I watch this log you sent me and I do notice that when it does manage to get the idle down near the 700 mark that the motor isn't making much vacuum and its fluctuating a lot in the high 60's kpa range which is about 10" of vacuum which inst enough for that car to run. That cam should idle with about 16" of vacuum or at about 45kpa on the map sensor reading and should fluctuate as much. I think that you likely have one or more rocker arms too tight when you adjusting your valves which is throwing that vacuum level way off. I would go through and loosen all the rockers about 1/2 turn and run that motor and log me some more data to see if the vacuum level improves and where we stand at that point. Once we get the vacuum level where it should be, I believe the motor will run much much better and then we will have your drive the car and log me some data and I will make an adjustment to the chips programming to see if we can get it to run even better.

 

could be the problem ,low vacum would affect the map sensor

 

ok im gonna have to readjust those things just to make sure they are not too tight and go from there thanks. does anyone know if you have to adjust the rockers when the motor is warmed up and running?

 

I would do cold not running zero lash plus 1/2 turn , Or like he said back each one off 1/4 and see

 

ok thats gonna be my morning chore, so im gona readjust them and let you guy`s know asap

 

Any luck yet?

 

nothing yet, this thing is crazy. ive allready went thru three different chips and all kinds of time and money, i dont know what else too try. i even took it to a diagnostic place and they said in closed loop its running fine but when i put it into gear i just dies most of the time or idles all crazy then kinda runs but not good at all.

 

If the rockers are ok you mite have to check your cam timing an make sure your not a tooth off.. I have seen it happen.. A lot

 

I have basically the same setup as you, and also had problems at first. The hotcam isn't going to make enough vacume, you will have to compinsate with more rpm's at idle. I keep mine around 900, 1000. You also need to take it to someone and have it tuned. TPI engines are very tempermental, what works for one won't necessarily work for another. I had a heck of a time with mine but finally got it going. Now it is loading up at idle, just started it when I freshened up the motor. Who knows.. Bump up your idle, double check everything else, and get a tune....