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5.7L Vortec running way rich, poor idle

I have a '99 Chevy Suburban 1500 4X4 with a 5.7L Vortec V8. It is idling bad and you can smell strong gas fumes. Revs good but there is a noticeable loss of power. The check engine light is on and we checked it with an OBD II code reader. P0300, multiple cylinder misfire intermittent code P0430, catalytic converter fault? intermittent code P0135, O2 heater sensor intermittent code P0135, misfire #7 cylinder, constant code

Changed plugs with new AC Delco 41-932 platinums, same as factory plugs. The rear 4 plugs showed rich with black deposits and #7 was wet (fuel). The front 4 plugs were lean, gray, nearly white. Plug change did nothing for the problem. New wires, cap and rotor and it still is running bad. Pulled the #7 plug and it is wet again. If you run it at

2k rpms you can see the unburned fuel being blown out the exhaust. I checked spark with an old plug and there is spark on #7. Also did a quickie compression check on #7 cylinder and got 120 psi within 2 cranks with the throttle plate closed. Will do a complete correct compression check later. #6 and 8 plugs are tough to get at with my old body. Looked inside the throttle body and it is carboned up lightly inside. I am going to run some decarbonizer thru the tank on advice from the local parts guys.

Would you believe the local parts place can't get a manual for this truck? They said they are a back order item. Guess I need to look online and see what I can find cause that does not sound right. It looks like a TBI system and there is an injector on either side of the intake. Is it possible that one injector is feeding the front 4 cylinders and the other injector is feeding the rear 4? I have searched user groups online for hours and it looks like a common enough problem but it also looks like there is no clear cut solution. Seems like folks are throwing parts at it and most never come back with any positive results. What do y'all think? I'll rename my first born male child after the person who gives me the fix. :-)

Reply to
billycarrjr
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Try replacing the O2 sensor.

Reply to
Sigwings

When my truck was acting like this it ended up being the temp sensor. It thought it was -30F. Steve

Reply to
Sven

The first thing I would try is replacing the O2 sensor at Bank 1/Sensor

1 (code P0135). This is a "pre cat" sensor and could be triggering a code in your converter too. A bad sensor could be screwing up your fuel mix and triggering misfire codes. Easy and inexpensive job, so no real loss if it doesn't fix your prob. Be sure to use high-heat copper anti-seize compound on the threads. Make sure it's not regular anti seize!!

JB

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Reply to
JB

Swapped the left and right pre cat sensors. Measure the heater voltage and ground on both sides, good. Still pops the same P0307 code. I have fuel dripping off the left exhaust manifold/header pipe connection.

Reply to
billycarrjr

I checked it with an ohm meter and it passes the book specs. Warmed it up and it decreases resistance as called for.

Reply to
billycarrjr

Reply to
Scott M

The 99' 5.7 liter used a distributor and a single coil.

Brian

Reply to
el Diablo

Pulled the upper intake cover (black plastic), reconnected the fuel lines and injector plug. Turned the key on to pressurize the fuel system and no obvious leaks. Going back out and pull all the pop off lines and crank it to see what kind of spray pattern I get. Interestingly the rear half is wet and the front half is dry. Got to be a leak back there. If anyone wants to see what it looks like under there copy/paste the following into your browser address bar and hit enter.

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Reply to
billycarrjr

Good news/ bad news. Pulled all the popoff lines and pressurized the system. #7 injector was spraying full tilt while none of the others were. Yeehaa! Got a fix. Run up to O'Rellys and they got a new BorgWarner injector for $60.00. Installed it. Repressurize the system and it still sprays fuel nonstop. Damn! Pull the connector on the injector pack and it stops spraying. Appears to me that I have a signal telling it to stay open. What now guys? Thanks for the help. Y'all pointed me in the right direction so far.

Reply to
billycarrjr

I checked voltages and resistance on the injector pack connector. Key on, 11 1/2 VDC on all 8 injectors. Other pin open circuit/infinite resistance on 7 injectors and the #7 injector has appx 560 ohms. Bingo! Bad input signal. PCM is faulty? What do I do next?

Happy New Years to everyone out there. Drive sober, I'll be out there on the road with you. Just not in a Suburban.

Reply to
billycarrjr

Check for a grounded wire between the injector and the ECM before you replace the ECM. Easiest way would probably be to just check resistance to ground with the ECM plugged in then not plugged in....GL

Reply to
Scott M

Disconnected neg terminal of battery. Checked ground signal wire on the connector for the #7 injector, appx 300 ohms to chassis ground. Unplugged the connector on the PCM labeled white. It is one of 4, white, black, red, blue. It is the top forward one. Ground went away. Plug it back in and ground comes back. I got a line on a cheap used PCM said to be good. Big question is - the Serv # on my truck and the Serv # on the PCM from the same make/model salvage truck are the same. Does this mean I can plug it in and drive? No need for a reprogram by the dealer?

I did measure the wire end to end for continuity and got an open. I am certain I was on the pins and the DVM is good and setup right. I was on the red black wire on the PCM plug and on the ground pin on the #7 injector plug. I have no idea why I am not getting a short there.

Reply to
billycarrjr

Just looked at your picture...I am not familiar with that setup but....It looks like it has pop-off type injector nozles. How many injectors does it have(the injectors themselves with the two wires going to them)? Is there 8? or just eight pop-offs? If it has 8 injectors with 2 wires on each it sounds like the ECM is the problem. If the truck is the same year and same engine and same # PCM you cant go wrong....btw from your picture it sure looks like it only has 2 injectors with 8 pop-offs on the end of the tubes. I dont have a wiring diag for that truck so Im not sure what the deal is with your ohms testing of the wires. Just remember that the ecm grounds one wire on the injector with pulses and thus open it and you can figure it out. So, does it have 8 injectors or eight pop-offs or what?

Reply to
Scott M

It has 8 injectors all stacked in 2 rows of 4. Each injector has a tube running out to a pop off/ poppet. We did swap #7 with a new injector so I am sure about the 8 injectors.

Found a guy on my motorcycle BBS with a schematic for this system. Ohmed the wire from the PCM to the injector pack plug. The wire is good and checked it at the pin on the PCM to ground and it reads appx 300 ohms to gnd and the injector pin next to it reads open as it should, Bad PCM. Just won a PCM from a '99 Suburban with the same Serv # for $35.00 shipped to my door. :-) He says it is good. We will install and if it starts run it down to the dealer and get it flashed to be sure we are right. I will post the results when it's all over.

Reply to
billycarrjr

Sounds to me like your new ECM will fix it for sure.

Reply to
Scott M

The problem was with the PCM. $35.12 with shipping from ebay and $73.45 to flash program it at the dealer. Got real lucky on the ebay find but always worth a look before you go to the salvage yard or dealer. It runs great now! Thanks guys. Saved me a huge repair bill at the dealership. The PCM I got was from an identical truck except it was from a 2 wheel drive and this truck is 4WD. It started fine with the used PCM but immediately died. Put the old one back and limped down to the dealership and after flashing the replacement PCM it runs great. Don't know why but there is some difference between the two that makes a big difference.

Reply to
billycarrjr

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