I have been working on my car for some time now. Back 7 years ago ,before I knew how to check fuel pressure, my 86E ran very rich. The injectors that we install were of unknow pounds. So, I didn't have a lot of time and it sat up for about 6 years. I had some trouble with fuel pump and fuel lines. I get back around to working on it and installed new Accel 24lb (don't laugh), new fuel pump, fuel line, fuel relay, MAF sensor, MAF relays, and NGK spark plugs. I have now got the car to idle fine and am able to drive it. It still runs very rich and can't figure out why. I checked fuel pressure with key turned on and its 44 psi, start car and it reads 40 psi steady. I turn the engine off and I noticed for every minute the pressure drop by 5 psi. Is this normal or does this tell me I have a leaking 1 month old injector(s)? Thanks for any help!

P.S. Today, I had a kid walk behind my car at the gas station and he was waving at his nose!

 

Your 86 came with 22 lb/hr injectors stock. By replacing them with 24 lb/hr Accel units you have made it a good 10% richer in all phases of operation. This is what a lot of C4 guys have done and it isn't a bad thing, just something the ECM must make adjustments for. The ECM can compensate for the 10% additional fuel rate of the 24 lb/hr units, but it takes several driving cycles for it to "learn" and make the appropriate adjustments in injector cycle ON time.

In order to see the problem and make the proper adjustments over the long haul, the ECM must have a well functioning O2 sensor to accurately judge the burned exhaust mixture and make the compensation changes needed. You should drive the car several times in different kinds of driving situations and then if possible get a scan of the ECM while it is operating.

If the O2 sensor is not up to spec the ECM will never get the adjustments right. There is only one O2 sensor in the 86. It is located in the exhaust pipe on the drivers side before the catalytic converter. Sometimes they don't go bad all at once, but slowly degrade in performance. If your O2 sensor is old and going bad but not completelyu dead it may not set a code, but it can give the ECM improper readings making an already rich running car stay rich or worse.

 

My O2 sensor is of the 3 wire heated kind. I replaced the 1 wire O2 about 6-7 years ago, but in that time period I have drove the car less than 100 miles. I have had codes that are fixed and cleared now, but I have been disconnecting the neg battery cable to reset them. I also know when you do this it resets the ecm's memory. So, I just need to drive the car and change plugs until it leans out? Any other suggestions could also help.

 

Forgot, Could someone tell me if my injector(s) is leaking from the first post I described?

 

The pressure is bleeding off, somewhere. Time for some trouble shooting.

RACE ON!!!

 

I don't smell raw gas anywhere around the engine bay or rear end. So, it must be bleeding internally. When I let the car sit for a few hours and screw on the fuel guage it reads 0 psi and no gas leaks from the Schrader valve. The O2 sensor is not giving any codes so it must be telling the computer it's o.k. Well sh**!!!

 

Leaky injector(s), leaking fuel pressure regulator, and leaking check valve are the common, internal, types of leaks. They have all been discussed in length, fairly recently.

RACE ON!!!

 

You say that it doesn't appear to be leaking externally and pressure is in the correct range when operating. That would cause me to assume that the rich condition isn't caused by the pressure regulator or a fuel pump problem. They may still be the a part of the cause for your rapid leakdown, but probably are not the cause for running rich.

Based upon the parts you have listed as having changed and the problem itself of running very rich, I'd suggest that you have a leaking injector. Could be one of the new Accel units as that has been known to happen.

I notice that you don't mention changing the Cold Start Injector (CSV) on your 86 when you installed the Accel units. The CSV was a "special" 9th fuel injector that was part of the 85-88 C4 fuel injection system. It could be the CSV is leaking or the thermal time switch that controls the CSV is faulty. You might want to start by checking the FSM for the "Cold Start Circuit Test" and diagnostics. It is Chart A-9 on page 6E-A-22 in my 88 FSM. Agent 86 probably has it scanned to PDF for the 86.

 

Try pinching the fuel preassure and return lines with vice grips after the lines are preassureised.

If the preassure still bleeds off you have leaking injectors, or the FP regulator has a blown diaphram.

If it does not, first disconnect the vicegrip on the preassure side, if it leaks down then the problem is the check valve in the fuel pump.

If it still does not leak down, remove the one on the return line, if it leaks down then you have a bad valve inside the FPR

 

This is what I thought of. I removed the FP fuse, had someone take each sparkplug wire off and use a new plug to check for spark while I turned the ignition. I have spark at each plug. Next I used a light tester and checked each injector plug and all lit up. I checked the CSV and no light, but I know the engine was warm and it shouldn't have lit up. I replaced all 8 injectors but didn't the CSV injector. This could be leaking . Ran rich before new injectors and after. The car runs pretty good, no missing, but from previous C4 ownership I noticed it is down on HP. I appreciate the suggestions. If anyone has thought of something else, let me know.

 

Also forgot the mention in this post that it takes 3 turns on the engine for it to start up when cold. Only takes 1 turn when the engine is warm. This sounds like it might point to the cold start valve as well!

 

The CSV is not connected to the ECM or influenced by the ECM in any way. It is controlled by the thermal time switch only.

If it starts better when warm and worse when cold and you suspect a leaking injector, the obvious culprit is the cold start injector (CSV) or the thermal time switch that controls it, or both. Get a copy of the diagnostic chart for the Cold Start Circuit for your car and do the tests in the order defined. It will help you solve the problem.

 

I am interested in seeing if this could be the problem. I will look in my FSM today and study a little on the CSV. I understand that the CSV is used until the engine temp reaches 95* and is controlled by the coolent temp switch. I haven't tried to the test that Jerris posted yet, but will. Any more suggestions might be useful!

 

I see in my FSM that there is a way to test the O2 sensor, but only if there is a code 44 or 45. Is there a way to test it without codes? What should the volts be? It states 1.0v for rich and .10v for lean. Should this number be some where in between for perfect ehaust mixture. I have thought about buying a new one to try out. That is after I test the fuel system for leaks.

 

When operating in a properly adjusted system the O2 sensor voltage fluctuates between 0.10v and 0.9v. It should average close to 0.45v. with constant transitions above and below that value. A lean condition is indicated when the average voltage is below 0.45v and a rich condition is indicated when the average is greater than 0.45v.

You can use an ocilliscope to see if it is working and where it is spending most of its time. You can also use a scan tool that shows/charts the output seen by the ECM as a waveform like the Ease, Autotap, or Datamaster, scan tools. Unlike a direct reading of the O2 sensor by the ocilliscope, even with the best scan tools you are still relying on the ECM to tell you what it thinks it is getting from the O2 sensor. So, while it is unusual for the ECM to lie about the O2 sensor inputs, it can and does happen when the ECM is defective or there is a problem with the wiring/connection from the O2 sensor to the ECM.

Good or bad, the ECM is not going to fake the O2 voltage transitions, so if it reports that an O2 sensor is varying voltage output in a reasonable range, the O2 sensor is probably good. If it says O2 voltage is varying between 0.10v and ~0.40v and you are running lean, then the O2 sensor is probably good. Conversely if is varying between ~0.40v and 0.90v and you are running rich, it is probably good. I say "probably good" because an aged O2 sensor can be reacting poorly and its average voltage would be somewhat lower or higher than it should be compared to what the mixture actually is. That can throw off the ECM's mixtiure calculations, but usually doesn't make you run pig rich or destructively lean. According to Federal mandate, OEM Emmissions Control equipment is supposed to operate properly a specific number of years/miles without going bad or it must be replaced for free. I believe that mileage value is 60k.

If you have a fairly new (less than 25k miles) O2 sensor and you are not getting a code 44 or 45, the O2 sensor is probably fine. If a scan tool shows active voltage transitions between 0.10v and 0.90v your sensor and its connection are probably fine.

On the OBD1 vettes with the 12 pin ALDL, if you short pins A and B with a paperclip while the engine is running you put your ECM into Field Service mode. Your manual is probably similar to my 88 FSM which states in Section 6E, page 6E-5:
If the Diagnostic terminal is grounded with the engine running, the system will enter Field Service mode.
... In "Open Loop" the "Service Engine Soon" light flashes two and one-half times per second.
In "Closed Loop" the light flashes once per second. Also, in "Closed Loop" the light will stay OUT most of the time if the system is too lean. It will stay ON most of the time if the system is too rich.

The ALDL has 2 rows of terminals with the top far right being "A" or ground and the terminal to its left being "B" the Diagnostic Terminal. Short them with a paperclip or a wire with tiny clamps on the ends. Doing this with the engine running it goes into Field Service mode. With the engine off it puts the system in Daignostic Mode and displays any Diagnostic Trouble Codes (DTCs) stored in the ECM.

Now, without a scan tool, you can do a limited scan of your system that tells you if the ECM is in closed or open loop mode, and when in closed loop if it is compensating for a lean or rich condition. If it goes into closed loop with no codes set, the ECM is seeing voltage transitions from the O2 sensor within an acceptible range, which would indicate but not gaurantee, that the O2 sensor is working correctly.

 

I have run a Field Service mode and the ecm says that it is in closed loop. The check engine light flashes every second after warm. I have taken the O2 sensor out and the tip looked good (gray brownish color). I took the spark plugs out and the white insulator was black and smelt a little like gas but not saturated. The fuel pressure is normal with a slow decrease after shutdown. I read somewhere that a fast decrease in pressure is either a leaking injector or a FPR. I checked the vacuum on the FPR and no gas. I would hate to think that a new injector would leak, but anything is possible. I still haven't checked the test that Jerris posted and haven't checked the volts on the O2 sensor, but will when I get time. The car aslo shakes a little when idling. The engine timing is at 6* btdc and have checked the TPS volts (.54v closed and 4.0 open), IAC by cleaning and testing and set minimal idle to 450rpm, PCV has vacuum and moves, distributer show spark on all 8 and exhaust seems to flow good, might rule out blocked cat, and also a new MAF install. I have read up on the CSV and this could still be my problem if in deed it would leak after car is warm, but need to do a good test on it as well. Engine oil smell a little like gas.

I am thinking about taking it to a mechanic shop and putting it on a diagnostic scan tool to find out what the real culprit is if anything. If my injectors, O2 sensor, and vacuums are good and showing no codes is there anyting else I should check for before going to the shop? I just hate to drive it around smelling like an old pickup truck, but the ecm might just need time to adjust to new injectors. Any more suggestions?

 

You put the ECM into Field Service mode and you report that it is going into "Closed Loop". It is important to note whether the ECM thinks the mixture is rich, lean, or normal.

Does it spend more time ON, OFF, or does it appear to be equal when in closed loop? If it is ON more than it is off, the ECM is aware of the existing rich condition, but is unable to adjust injector cycle time to offset the problem. I would assume due to a physical problem cause.

If it is OFF more than it is on, the ECM sees a lean condition where one does not exist and should be trying to compensate by making the mixture richer. I would guess an electrical/sensor problem.

Knowing what the ECM believes is going on can help point to the root cause which may be an invalid value from the sensors or a physical problem due to vacuum leaks or other mechanical problem.

 

To me it appears that the light blinks one every second and sometimes it stays off longer. I did noticed it blink twice every second when it was in open loop with a cool engine. By me checking the volts while in closed loop will this give me an idea of the O2 sensor sending the right signal? Is it a good idea to have my computer put on a scan tool? I don't think they charge.

 

I got home from work today and tried a few things. First I screwed the fuel pressure guage on. Turned the key and noted 40psi. Then it took four key turns to start the engine. The guage said 36-37psi while running cold, I then tapped it to my windshield. The exhaust smelt rich but not so damn rich it burned you eyes. I let the temp get to 150* and inserted my code key in terminal A & B. Light flashed one time per second.

I drove approx. 3 miles total and noticed when I gave it throttle or came off throttle to brake the light would stay on for about 2-3 sec and then go back to every sec. Fuel guage would go to about 43psi when I gave it throttle and back down to 37psi when I came off. Got back home and (had already taken gas lid and rubber neck off) and tested the fuel lines. Pinched the fuel feed lines and pressure didn't change. Pinched the fuel return line and pressure increased to about 60-70psi quickly. I haven't checked the O2 sensor volts nor have I checked my gas mileage yet. The car has never ran this good. It idled good once warm and throttle responce was good. The exhaust still smells rich, but I might need to give it some more time for the ecm to adjust to the injectors. Mike 88z51 seems to be about the only member willing to help me on this one. After reading this does anyone seem to know why it is still smelling rich.

 

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