ZachSRP

Hi so I'm new to these forums but I'm not new to cars. I'm 17 years old and my daily driver is a 1990 300ce Mercedes Benz that my dad and I have fixed up over the last year and a half. I definitely know a lot more about cars now than I did before. About a month ago I purchased a 1991 Camaro RS with I think a 305? TBI. Anyways we've already fixed a good amount of issues with it but I'll let the engine warm up and go into reverse and it will stall and die when I give it a decent amount of gas. When the car is cold it doesn't have this problem. I'm pretty sure my Tach is wrong but it idles around 4-5k on the tach cold start. If I let it warm up and restart it, it will idle around 2k in park. I don't know how long the car has sat for but the carb has to be dirty or just bad. Anyways when it stalls I also have almost no oil pressure on the gauge. If it's working correctly. When it idles at 4-5k the gauge points only half way on the oil pressure. Any tips? Common problems and fixes? I'm new to carbs and v8s. I'm going to be posting a lot on here in the future. Also after a decent amount of time idling the check engine light will come on. Not every time but almost every time.

ZachSRP

No ideas?

L98_383_Stroker

You say TBI at first, but then say carb. Just to be clear, does it have a carb or TBI. They are similar in shape. Post a pic if you need help identifying it. Either way, idling that high almost assuredly points to a vacuum leak. Is the TBI or carb bolted tight? Look for vacuum lines not connected. You might want to post a picture of the motor top end with the air cleaner off.

ZachSRP

Alright thanks! I'll post a few pictures when I get home

ZachSRP

RBob

iTrader: (1)

For the tach reading high, see the electronics board here. Up top in the sticky's is the fix for it.

For the check engine light, blink out the codes and post which one it is.

RBob.

RBob

iTrader: (1)

Posting while you were... That is a TBI set up, which is fuel injection. At idle observe the spray pattern from the injectors. Should be a nice even cone of fuel.

RBob.

ZachSRP

Thank you! Will do

ZachSRP

Yea the pattern is an even cone. Any idea as to why it dies when giving it gas in reverse? Only when the engine warms up

Schurkey

My first thought is that the fuel pump relay--or the signal to activate it--is somehow defective.

When the oil pressure goes away, the oil pressure switch no longer powers the fuel pump.

The oil pressure switch is the "back-up" power source for the fuel pump relay.



Therefore, the next question is whether the oil pressure is GENUINELY low, or do you have a defective oil pressure sending unit. Defective sending units are common. Replacing it with a mechanical oil pressure gauge that is known to be accurate would tell you whether or not the oil pressure is as shown on the dash gauge.

After verifying oil pressure and the fuel pump relay (fuel pump power) circuits, I'd want to spend some time with a REAL scan tool to determine what the computer thinks is going on that requires an indicated 4,000+ rpm idle speed. (Best Guess: Tach is wildly inaccurate) With the scan tool connected, any number of other problems might be discovered as well.

How long since the last THOROUGH tune-up?

ZachSRP

No idea I just bought this car a month ago. I have no idea what the previous owners have done to it besides taking shortcuts. They ran wires for a temp gauge, horn, and subwoofers through the door jam. We fixed the temp gauge on the dash all it was was the temperature sending unit. We also added a switch for the electric fan, the right way. But I'm going to buy a new distributor cap and rotor spark plugs etc. what spark plugs would you guys recommended for my 305 tbi? Also what are some good plug wires? Where's the fuel pump relay located? Also the exhaust is all messed up too if that could effect anything.

ZachSRP

Just pulled the codes....23 and 53. Keep in mind the exhaust is all messed up. I'm going to get it fixed soon and hopefully that will make it run right..

RBob

iTrader: (1)

For spark plugs I'd run an Autolite copper core plug, nothing fancy. Not sure which is the right number, likely a #24 plug.

Code 23 is IAT low, if you ran the engine without the air cleaner that can do it as the IAT is mounted in it. And would need to be unplugged to remove it. Although, looking at your picture I don't even see the connector/pigtail for the IAT.

Code 53 is VATs failure.

RBob.

ZachSRP

Thank you. Where exactly is the IAT connector supposed to be at? 53 says system over voltage (ECM) is that the same as the VATS? What would cause a system over voltage? Or would that cause any of my bogging issues when warm?

RBob

iTrader: (1)

The IAT connector should be close enough to the air cleaner to plug it into the IAT sensor. It is a two prong plug with a tan and a black wire.

On the TBI systems code 53 is VATs. On the '90 - '92 TPI & MPFI f-bodys, VATs is 46, with over-voltage being 53.

RBob.

ZachSRP

UPDATE* So I just got a dual exit exhaust installed. They cut the cat off and just installed a flow master muffler. I can definitely feel a difference in throttle response and it sounds pretty good. Driving it on the way back though I still have the same problem, every time I left of the gas to come to a stop it will completely die. Then I have to put it park and redo this every time. It's only when the engine temp starts to warm up. On the way there I drove it cold so it was completely fine. Now that I have an exhaust on it I can tell there is definetly a misfire on at least 2 cyclinders. I'll be buying new plugs and wires and probably a dist. Cap and rotor. Could this fix my issue of it dying when warm? I don't know what else to try as of right now. Fuel filter?

L98_383_Stroker

If you are sure you have a misfire, you really need to fix that first. The ECM will be lost if there is a misfire. You are dumping raw fuel on the oxygen sensor. The ECM will lean out the mixture trying to compensate. The cylinders that are firing then have a lean mixture and poor performance. Get it running on all 8 cylinders first. Reset all codes and see what codes come back. If no codes come back, then you will have to advance your skills and datalog the car! Good luck!

ZachSRP

Thank you! Just waiting for parts to come in

Schurkey

TRUE!

Exactly backwards. Common misconception, though.

It's an OXYGEN sensor, not a FUEL sensor. When the engine misfires, the fuel doesn't burn, so there's LOTS of free oxygen in the exhaust stream. The O2 sensor reacts to the excess oxygen, sends a "lean" signal to the computer. The computer reacts by RICHENING the mixture.

Getting it running on all eight, and erasing the codes is not a bad plan, but I'd suggest looking at the data stream with a REAL scan tool, and not just waiting for the "Check Engine" light to come on.

ZachSRP

Put in spark plugs and wires and also a fuel filter and still having the same issue. Dies when the engine is warmed up in gear. Any more ideas? I've read about the same issue but nobody said what they did to fix it.

Schurkey

What you do to fix it, depends on what the actual problem is.

Have you bothered to put a scan-tool on the vehicle yet? What does the data-stream show?

I'd especially want to know about IAC operation, commanded idle speed vs. actual idle speed, short- and long-term fuel trim numbers at idle just before the engine stalls. and O2 voltage just before the engine stalls. Those are not the only important factors, but that's where I'd look first.



My pickup had a high-speed misfire that got worse and worse until it stalled at idle. Turned out to be a faulty pickup coil in the distributor. I had to replace the distributor mainshaft to fix it--although replacing the distributor with one having a good pickup coil would also have worked.

ZachSRP

Installed a new IAT sensor today and it made a big difference. The idle is steady now and it idled down a lot. It doesn't fluctuate up and down anymore. When the engine temp was all the way warm the idle stayed steady. It still died when I put it into Reverse and gave it gas. Thinking of buying a new MAP. Opinions?

Actually I read more about the IAC and I'm thinking about replacing that first. The symptoms of a bad one are the exact same as what I'm experiencing

Schurkey

Yeah, don't bother to do any diagnosis. Replace a fistfull of parts, and hope the symptoms go away. If not, replace a bunch more parts.

ZachSRP

Lol. Cleaned the EGR valve and the problem went away. Only thing I've replaced was the IAT which was $15. So no I didn't replace a fistful of parts.

ZachSRP

New EGR valve. Car runs perfect. Doesn't want to stall at all now. Time to work on the body, brakes and suspension