rlemaire

I have a 1982 with the cross still intact (except missing the smog pump) I was having trouble with the motor idiling down correctly, sometimes it would go down to around 600 RPM and some times around 1000 RPM. Yesterday, while driving it began to run very bad. It would only run if I kept feathering the throttle.(kept pumping) When I was able to get it home to inspect I found that the injectors seamed very lean not allowing enough fuel to keep the motor running. I unpluged the vacuum from the MAP's sensor and the injectors went rich allowing the motor to run, but rich. I replaced the MAP' sensor with a new one but still does the same thing. There does not seam to be any vacuum leaks on the intake anywhere (TBI base or base to intake plate)
ANY IDEAS ON WHAT I CAN CHECK ?

Big2Bird

Cap off all vacuum ports except the Map. See if it improves. This will show if you have any other vacuum leaks.

jdp6000

Its not that simple. Was it running right before? assuming it was....

When you turn the key to on do you hear the fuel pump (from behind) kick in for 2 seconds? Is the engine light on?

I'll guess but chances are its either the CTS (coolant temp sensor) at the front of the engine or the O2 sensor( down on the pipe just infront of the cat).These two items tell the computer how lean or rich the gas should be.

Make sure your coolant level is up. The CTS doesn't work right if the level is low.

You can also check the connection on the TPS. Its on the side of the rear TBI.

Just some advise. Don't start trying to adjust things...like the TBI settings or loosening off the TPS. You will compound the problem.

Jim

rlemaire

Jim,
When I got the car I can only assume that things were not right as it did not run.
However, as I mentioned it seamed to be ok yesterday but instantly went bad.
I did cap off all vacuum lines but seen no difference.
It is pumping fuel but with the vacuum line attached to the MAP (new) sensor the motor does not get enough fuel to stay running unless the throttle is feathered. With the vacuum line disconnected it will stay running but very rich.
No engine light, my guess is the bulb was removed or burned out.
Is there a way to check the CTS and the 02 sensor?
Is it possible that the ECM is bad but still allow fuel management to adjust when remoming the vacuum line?
I look forward to any information you may be able to share.
Thanks, Ron

shoptek

This is not a quick fix, or for the electronically/computerly challanged but is good for the long run and any future issues-----years ago I did a Google search and put together an ALDL interface using an old style serial cable, some resistors and diodes and a freeware windows program that gives you real time feedback from the OBD I style interface.
I have not used it in years, but when I did, it showed my CTS way out of wack and my TPS was not changing states on our '82 CFI
True, you can use a simple DVOM, but you need to then ck. everything 1 by 1.

rlemaire

Did you not include something or am I totally lost

shoptek

http://winaldl.joby.se/

Yeah...I guess the link would help.

I thank the people who made this program and the instructions for the cable. It works nice!

jdp6000

No real easy way to check the O2 and CTS. I would change the CTS...its cheap. You really need to know what codes its throwing.

You can reset the ECM by pulling the fuse near the battery. keep in mind by doing so your IAC's will not work until you can get out for a drive...its how they reset.

Whats your MAP pressure. Hook up a vac guage to that port...should be 20 psi and steady...19 is okay as well.

Can you see if they monkeyed around with the TPS....look at the nut...does it look like it was tampered with??? The TPS tells the ECM if ou ar at idle or WOT. Range is .525 volts (set at engine off ignition on) to 4.5 volts.

Tech article on how to set the TPS and a bunch of other stuff. don't mess around with the TBI's at this point..http://corvettefever.com/techarticles/4688/index.html


Jim

jdp6000

You really need rule out a bunch of stuff here. The list is long. How is the PCV. Does the EGR work (push up the diaphram, plug the hole, should hold)? Check and clean all the plugs on the distributor. check and clean the Two plugs at the ECM. all the injector wires run around to the passenger firewall...there at least 4 plugs in that box that corrode.

As for vaccum leaks. Check for the 20 psi. Gentley tighten the throttle plate bolts and TBI bolts.

Does it look like the TBI's were messed with...if so the caps on the access ports would be gone.

fuel pressure is the biggest problem with these cars. check the fuel filter.

rlemaire

Jim
It looks like the TPS has been changed so I have it set @.5v and there is 20 inches of vacuum.

rlemaire

PCV OK,
With the MAP vacuum line removed I can compress the EGR from the bottom side and the motor slows. All plugs on the dist. clean as will as the 4 plugs on the firewall and at the ECM. Caps on the TBI's are gone but the settings seam visually ok. Fuel filter is clean.
As I said it was running ok and went bad while driving, I came to a stop and when I took off again the trouble started.

rlemaire

Something new to add.
I got the check engine light working now and with a cleared ECM get no codes unless I unplug the MAP's sensor.
HELP!

terry82

you said that the tbs has changed .i would check that again .you can check this with a ohm meter. when you move the throttle open and closed ,the reading should be smooth [the numbers should move low to high and back steadily not erratically] on a cross-fire i allways suspect a vac leak .on the back throttle body where the throttle cable attaches grab on it and move it. does it have much up and down movement ?does the rpm change ?the throttle shaft on the throttle body wears .

jdp6000

Reset the TPS to .525. Variance can't exceed .007. That puts you in a range of .518 to .532.

No codes? I would change the CTS and O2. I have seen cases where one or the other has gone bad with no codes.

20 inches of vac suggests no vaccum leaks. Thats good.

How carboned up are the TBI's? Look in the holes where the IAC needles are...is it clean??? Try decarbonizing if they are dirty.

Jim

rlemaire

Jim, In one of your first post's you said that the fuel pump should run for 2 seconds then shut off. If I listen with the gas tank cap off, I can hear fuel running back in to the tank so if the pump is suppose to shut off, I wonder if there is a split in pump assembly. Is that possible? I think I will try to pinch off the return line to see if the noise in the tank stops and also check fuel pressure with a gauge. What are your thoughts?

jdp6000

It probably is the fuel pump. You should hear the pump kick in for 2 seconds and thats it. With the key in the on position when the car is cold right after you hear the fuel pump you should hear the injectors kick in for a couple of seconds....its called the prime pulse.

Your problem could be entirely fuel pump. If the engine is starving for fuel...rpms drop....ECM calls for more fuel....rpms climb....etc.

If the pump has never been replaced change it. Put a 1985 pump in there. Higher volume. Will guarantee about 13 psi. Stock ran around 9 psi...not enough. If the stock pump is going and psi is below 9 it will cause your symptoms.

I changed CTS,O2 then fuel pump. I should have gone straight to the fuel pump. But CTS is about $15 and O2 is about $10.

Jim

rlemaire

Jim, Should I hear fuel running or flowing in the fuel tank with the ignition switch on but the motor not running?

jdp6000

No. Just for that 2 seconds. You shouldn't hear the buzz after that. If the pump is going it will continue to buzz. I've never hear the fuel running back to the tank. I'll go out and listen to make sure.

Jim

warrior2291

Jim sounds like the same kind of problems i had
Steve

rlemaire

Steve, What was the fix to your problem?