manfromoz

Hello all,
I was hoping to maybe get some advice on a problem I am having trying to get my crossfire to idle properly.

Let me start from the beginning. It has been parked over 20 years and several changes over time but not driven. I started putting things together and trying to get it finished so it can see sunlight again. I rebuilt the engine recently and put a new fuel tank and sender in it as well as a new fuel pump. I put on the old but never used x-ram intake and the throttle bodies were bored out and had a non factory fuel pressure regulator on the rear throttle body with a vacuum port on the side of it. ( I was told it was to hook up to vacuum line and would lower the fuel pressure at idle and when given more vacuum while driving it would raise fuel pressure) I replaced the ecm and with a kit that came from turbo city. (newer ecu and wire connector kit). The exhaust has the egr system removed and no cat in it. A new distributor from dei that claims it is a better distributor but still has the same 4 pin connector to the ecm.

I had to replace the fuel lines to the throttle bodies because I could not get the old ones not to leak. After checking everything I could think of I started it up and ran smooth but had a real high idle around 1600 rpm and some times even higher. I connected a vacuum line to the fuel pressure regulator I mentioned above and the idle would lower to 1200 rpm but could not get it lower on its own. I connected a vacuum pump and started to put a heavy vacuum on it and started to get the rpms down to about 1000 rpm but had to keep cranking on the pump.

I came across a nos top plate with both throttle bodies from gm still sealed in box from last century. I replaced the throttle bodies with the new ones and when I started it up it idles about 1200 rpm and as it warmed up it would lower. When it lowered to 800 rpm in a short time I was thinking great but as it lowered down to about 600 rpm it started to surge.

Surges from 600 rpm to 1200 rpm and doesn't want to not surge unless I apply the fuel pedal and raise the rpms.

I do have a gm shop manual and it mentions to check wiring for shorts in 420 and 422 to trans converter clutch, circuit 424 hei bypass, 423 est and 422 tcc.

I have not found any shorts.

I was thinking maybe temp sender to ecu and checked voltage in wiring and even replaced the sender. the sender is inside a sleeve and then into the intake and tried to relocate into a thermostat housing with ports on the top of it but it wont fit due because the outlet of the thermostat housing hits the heater hose connector in the intake.

I thought about getting the renegade intake but didn't want to spend the money on a different intake if it was going to still surge. (i wouldn't mind changing it but want to get surge gone 1st)

I do not believe I have any vacuum leaks. or can not get a idle change when I spray everything down with carb cleaner while it is running.

Any suggestions would be appreciated.

Thank you

Vetteman Jack

Moved to C3 Tech/Performance Section.

terry82

yes I would rather have the new renegade intake but that is not your problem.I would check the iac.https://www.yourmechanic.com/article...-control-valve I also would would wonder if the computer may have to learn., when you make changes the computer sometimes has to relearn whats going on. a couple of miles down the road may help.Not familer with your fuel pressure regulator.i would take that out .the rear tb has a regulator.make changes one at a time .so many parts have been changed from stock they all need to be checked to see if they are working right.

manfromoz

Thank you for the reply.

The new throttle bodies came with new iac valves and a new tps. I did not put the fuel pressure regulator from the bored throttle bodies on the new throttle bodies so I currently have the factory fuel pressure regulator.

Earlier this morning I tried to drive it and I had to press lightly on the fuel pedal or it would sputter bad but then would go good. I noticed the speedometer was not working but I decided to go further and after a few blocks it wanted to bog down and sputtered when giving any fuel. I decided to turn around as not to get stranded too far from home and it did stall when turning around. It started right back up without any problems but when I put it in gear it runs real bad and wants to stall. Almost back home and it stalled again. Would start back up fine and can rev it up if I am in park or neutral but once I put it in drive it would die. That occurred several times but when I put it in reverse it would stay running but real rough. If back into neutral would smooth out again. I was able to back it up onto a side street and shut it off for a few minutes. When I started it back up I was able to put it in drive and limped back home. At that time it sounded like I had a major vacuum leak if i tried to give it any gas.

When I got back home I noticed coolant leaking from the upper radiator hose. I cleaned things off and tightened the hose and now no leak. Using carb cleaner i sprayed around the throttle body base plates and noticed a idle improvement. I tightened them down a little more but still notice a idle improvement when spraying around the throttle body base gaskets. MY neighbor recommended I double gasket them but have not done that.

Now it sputters in drive but can reverse without any problem at all. I rechecked timing and it is at 10 btdc with est disconnected. I found my lower speedometer cable is broken and ordered a new one.

The tps has exactly 5 volts to it and I am trying to find how to adjust the tps in my manual.

I will check the iac valves as soon as I check and adjust the tps.

It started snowing here so I don't think I will be able to drive it until the roads clear up some but will check iac valves as you advised.

If you have any other thoughts or recommendations I would greatly appreciate your input.

terry82

new iacs with new throttle bodies that is great .but you do have to adj the tps and you need to check https://www.bing.com/videos/search?q...3&&FORM=VRDGAR

terry82

I would ask buccaneer if he has any more rightups on how to do these http://www.superchevy.com/how-to/468...system-tuning/

DUB

Have you attempted to balance the throttle bodies???

Do you know what your fuel pressure is at???

Your speedometer cable beign broken is not good due to the ECM has no clue on what your speed is so driving it at this time is pointless. There is no way in gettign your IAC's to 'learn'.

I WOULD NOT double gasket the throttle bodies. Or at least I have NEVER needed to do that.

Do you have a scanner ....because the MAP volt reading can tell you right away IF you DO have vacuum leak or not.

Also with a scanner..you can see when the ECM goes into CLOSED LOOP and I have had a few that when it goes into CLOSED LOOP the idle will start to 'hunt' and I have found it was fuel pressure causing that.

DUB

manfromoz

Thanks terry82 and DUB,

I do have a scanner I will need to pull out of storage tomorrow after current blizzard is over.

I have not tried to sync the tbi's - I just figured since they were a new assembly from gm still sealed and attached to the intake top plate that they were already in sync but I know not all things are as you would think they are. I will have to get the correct meter to be able to check them.

I have been reading all the info I received with the vehicle. (including a printed copy of the link terry82 sent me. a copy from corvette fever)

I rebuilt the engine recently with the parts I received with it. (someone else's unfinished project - he was trying to do every change he had read about all at once) There were a lot of changes compared to stock that i used since they came with everything.

parts I used on rebuild were:

comp cam that was still in the package part number 12-465-4
gross valve lift .499 intake .493 exhaust
lobe lift .3120 intake .3080 exhaust
lobe seperation 113.0
It came with new springs

a fresh set of rebuilt double hump heads (The original heads were cracked)

roller rockers - I believe 1.6:1

x-ram intake without egr

ecm upgrade kit from turbo city using gm 7747 ecm

new fuel pump

originally i had a set of bored throttle bodies that were from the x-ram company but changed to a new set of original.

I ordered a fuel pressure test kit on ebay today so I can find out exactly how much fuel pressure I have.

I have been working on it a lot lately trying to get it all working properly but with the stumble and surging and now noticing it wants to backfire out the throttle bodies on snap acceleration in park that there were some incorrect mods being done.

I am thinking I may need to change the cam or heads but want to do all the checking and testing I can 1st. I've been reading through all the paper work and previous write ups that inspired the changes and all seem to match except for the cam.

I think I need to do some more research and pull out the scanner and wait for the fuel pressure kit to arrive before I make any changes

any thoughts??

manfromoz

My curiosity got the best of me and I bundled up and went out to the shed and got scanners.

I think I might have to get a new one for this one

My tech 2 doesnt go back to 82 models and I really dont know what my otc monitor 2000 is telling me

I go into mode 13 for map and it keeps fluctuating but as far as I can see it is checking voltage

any suggestions on a scanner to get?

Jebbysan

IAC or the gasket around the upper and lower intake has a leak. Take a propane torch with the gas on and unlit and sniff around for a leak. If there is one, it will pull the propane in and the idle will change and or stabilize.
The intake top gasket is a very common issue.....it dries out and fades away.

Jebby

terry82

http://www.winaldl.joby.se/

terry82

lots of crossfire tech saved here https://www.digitalcorvettes.com/for...d.php?t=101038

terry82

http://www.superchevy.com/how-to/51218/

DUB

I am curious. On the TBI's you have on it now. Is the idle screw area welded so you cannot mess with it??? It is going to be on the front TBI. 'Normally' this area was brazed or welded to keep that idle screw from moving and people tampering with it and I have to cut the brass or weld to allow me to set the TBI's and then secure it again.

I do not know but I think your larger TBI's would or m be better than the factory ones due to allowing more air in for the cam you have.

AS for the backfiring through the intake...it may be ignition related or possibly a stuck exhaust lifter An exhaust lobe is wiped out or valve is not opening thus allowing the compression stroke to come back into the intake because it has no where else to go..

As for a scanner...you need to look and make sure it will work for your year model. I have TECH 1 and it works but it is old but you can find them.

Look at the link in POST#12 in the thread below. I cannot say if it will work due to not spending any time researching this one.

https://www.corvetteforum.com/forums...r-rebuild.html

DUB

Buccaneer

WOW! you have a lot of things going on. Sort it all out before doing any mods for sure. You most likely (have/still have) a vacuum leak which is causing the high idle. You DO NOT have to double gasket the TB base gaskets for any reason. You can double gasket the tower gaskets to raise the pod out of the TB opening to gain more flow though. We have proven this on a flow bench testing various TB configs. Also, just because your TB are NOS new, does not mean that the TBs are balanced properly. A easy way to see is to look down the TBs and slowly open the throttle by hand (engine OFF) and watch the throttle plates to see if they open at the same time/rate and if they are closing at the same place/gap. This may take a couple times while watching closely. Another quick, down and dirty to get you into the ballpark is to take a slip of paper (cut into strips about and 1/2 to 3/4 wide and 3-4 inches long) and open the throttle again by hand and place the strips under the plates (rngine off). Close the throttle and then pull the paper up slowly, you should just feel a little drag on the paper (the same tension) on both TBs. If you do, you are close for the balance, if there is no tension they need to be adjusted more closed.

After you make ANY adjustment on the TB plate angle (balance) YOU MUST readjust the TPS sensor. This sets the voltage so the ECM knows where idle is supposed to be. Set the TPS (engine OFF, key ON) to .525v and you are good to go. You may need to play with it a bit since when you tighten the screws down, it will change. The .525 setting is needed no matter what. GM is a little liberal on that tolerance, but you really need to get it as close as you can to .525v.

x-ram intake without egr... If you have this manifold on your motor now, this will be an issue as far as performance goes, jus sayin'.

ecm upgrade kit from turbo city using gm 7747 ecm... I'm a little confused on this one as far as what you are trying to do. Do you know what PROM you have? Is turbo city even in business anymore doing anything CFI? I haven't heard of them in a very long time. Instead of going that route with the ECM, I would have just gone with a chip in your stock ECM with what you have done to the motor. If your dur of 312/308 @ .050 is correct, you should have been ok with the stock ECM. It is the duration that will kill you/ECM when you start getting too far from the stock cam config.

I was also wondering about your dizzy, you said DEI, do you mean DUI? Also, a stock module is not a four pin, it's a 7 pin and if you have the DUI dizzy, you should have gotten a 7 pin module for the GM HEI dizzy.

Hope this helps out a little, good luck with your 82 project.

corvettenorway

do you have a pcv valve ?? are the front and rear injectors in the right place ?

manfromoz

Thank you all for all the information and things to look at.

- I am going to do some more research on a scanner and making or getting a manometer as advised by terry82

- In the mean time I am going to try the paper inspection Buccaneer advised on and look further for any vacuum leaks as advised by Buccaneer and jebbyson.

- The current throttle body's still have the idle screw brazed so it can not be adjusted but I will cut the weld if needed to make adjustments as mentioned by DUB. I did have a steady idle but high rpms with the bigger throttle bodies. When I put the nos throttle body's on I got the lower idle but a big surge.

- I am concerned now about not having egr for possible performance concerns. I do not have any of the egr parts other then a extra set of stock manifolds in good condition. I would have to look for and locate the egr and metal tube that crosses along the front of the engine. I do have the air pump in a box and I think the brackets are there also but not on the vehicle.

- The ecm kit was bought from turbo city in 2004 and was still in the box. I will have to get the prom information off the side of the ecm. It had a sticker with all the info on the side of it. I do have the original ecm and the original connectors also. I followed the instructions and changed the connectors and have double checked all the wiring to confirm connected properly to the 7747 ecm. I did mean DUI not DEI and when I said 4 pin I ment the connector to the harness that connects to the harness. (sorry. I know giving correct information when asking for advice is very important and should have been more specific what I was trying to say)

- I do have a pcv valve on the left valve cover and connected to the manifold.

- I hope I don't have a cam problem or a stuck valve but can not rule them out. I don't get as much of the backfire through the throttle bodies with the nos as I did with the bored out ones I removed. I was hoping it was a timing issue. It is hard to set the timing when the vehicle is idling at 1200-1600 rpm.

- All the parts I used putting this together came with it and I read all the paperwork and articles I received with it before taking on the project and seemed to make sense to me at the time but I'm learning a lot after getting it all together.

- I should get off from work early tomorrow and plan to spend some time on it again. I do need to re-adjust the tps as I have set incorrectly. I thought I read somewhere on a different forum to set it to .575v even though manual said .525v.


I really do appreciate all the help and advice I am receiving and will eventually get this all worked out I hope

terry82

I think the cam and the distriubter are okay .I think the tbs need to be .525.then adj the timing..would not worry about the egr.for now .keep reading ,it all will fall into place, for you.

squared

Wow, this brings back some memories..I didn't think anyone was still driving these. I bought a brand spankin new 82 Z28 with the 305 crossfire injection as my ensignmobile. Man, what a pain in the a$$ that car was. The car had these flappers on the hood that came up when you floored it. Great visual, but it was a flawed design and I broke a valve at 16k miles due to what I believe was water intrusion into the intake. In those days, warranties went to 12k and I was SOL with Chevrolet on getting them to fix it under warranty. So I decided to fix it myself and save the labor, put myself through college selling auto parts and had put a V8 in a Vega, so I figured it was not going to be that hard...so I thought.

I decided to go with a 350 in lieu of the POS 305. Went down to the local NAPA and ordered a 350 long block, I was assured that I wouldn't get an engine with dished pistons with low CR, but they lied. Decided to put headers on it, the O-2 bung being welded in one of the primaries in the left bank. Computer controlled injection was new at the time, I'd spent most of my life tuning Quadrajets. So I ordered the factory manual and other books and set myself to learning everything I could about the GM "triple C" system. Learned a lot, spent a lot of time monkeying with the thing but never was able to get it to run just right with the 350. Figured it was an algorithm/airflow issue, so I bought a PROM for a Corvette and put it in the ECM. Didn't fix it, still got the occasional check engine light.

Any chance that the throttle bodies you got were for a 305 Camaro and not a 350 Vette? I'm a nov at the parts bin on these two engines, but given my (foggy) knowledge from last century that could possibly be an issue(?)

DUB

I know that getting this to work may be a slight challenge do to so much is going on.

I HONESTLY believe that once you balance the throttle bodies as the GM manual outlines it may help you out. I can say that getting the rear wheel to stay in a locked down position so when you have the car in drive can be a challenge. Because raising the rear of the car and trusting the park brake oftentimes just does not work well during this process. I have what some may feel is an unconventional way of doing this but it has worked for me on numerous occasions with no ill effects.

I wonder if the bored out TBI's have had bushings put in it where the throttle shafts are and have no play in them. I would have to guess that the NOS TBI's you have are good and solid with no free play in the throttle shafts. Also...I have dealt with the bored out TBI's and it seems when they do this boring out...they effect the ported port where my manometer is attached so I HAVE TO use a feeler gauge to set the TBI's an hope for the best. Having the bored out TBI's is not a bad thing...because I have three 1982 and 1984's with them that run great.

Your MAP sensor voltage will tell you a lot when you get it down to curb idle if your have a vacuum leak or not. It should be...if my memory serves me correctly about 1.4 volts.

Keep in mind that you will still need to drive the car to set the IAC's....so surging or a weird idle may still be present even after you get it all set.

DUB