350 5.7 TBI Timing/Fuel Issue

[Jeepcrazed]

I've been off-roading for over 20 years and had several modified Jeeps with various motors. I recently purchased a Jeep CJ7 that already had a 1993 Chevy C1500 TBI 5.7 motor in it. Guy who had it wheeled all over the Southeast and out West. He let it sit in his basement for a couple years due to his work travel schedule. He decided to sell and went to fire it up. It would idle fine but he couldn't even drive it up the driveway (on a hill) as it would stall when you gave it gas. Now you could rev the motor all you want sitting still but once in gear (it's a manual - SM465) and gave it gas it had no power.

I pulled the trigger and bought it at a discounted price. I got it home and replaced the fuel filter (it was pretty dirty!). It ran better but still had power issues and would throw a Code 42. I replaced the EST circuit and ignition module. No change. Played with the motor for several weeks with new injectors, map sensor, IAC, fuel regulator, TBI rebuild, knock sensor. Checked all wires for open loop, bad ground. Added more engine grounds (body to frame, body to battery, frame to battery, etc). Forgot to mention, the timing was checked (set to 0 with bypass wire disconnected) I replaced the computer (16146299). Transferred the AWLB chip to the new computer. (There is not catalytic converter and muffler was taken off and run to see if there was an obstruction in it as well.) A couple weeks ago I went for a test drive in the neighborhood and all of a sudden I had POWER! The throttle had a lull in it but it would GO! Ocassionally it sputtered when I got on the throttle but would get it. The next few days it went right back to normal. NO POWER.

I broke down and took to a mechanic. He was stumped. He said the best he could get it to run was disconnecting the bypass wire and advancing the timing (basically eliminating the computer control).

Since I planned on do a major overhaul on the Jeep I began tear-down. I pulled the cage, built a new dash with all new auto-meter gauges, put in new fuel cell (along with all new fuel lines), new carter p5001 fuel pump, new crate motor from Summit (replaced with same motor, stock 5.7 TBI) and installed a Painless wire harness (wanted to eliminate any wire issues). I even got a new eprom and installed it just in case the old one had gone bad. I have a fuel pressure gauge on the back of the TBI (supply side of course) and it stays at 12 PSI. I tried an adjustable FPR, but turned all the way down it was at 14-15. The motor is running rich.

Like I said before it will start right up and idle (even though it doesn't sound like a healthy idle) but when you try to drive it, no power. It will also backfire through the exhaust when you give it quick throttle. Painless calls for using the 1227747 ECM, with ASDU eprom and 16060836 calpak. I have the ECM and eprom and I'm waiting on the calpak to come in the mail. I'm gonna try the new computer/chips and keep my fingers crossed but doubtful.

Any reccommendations?

[1project2many]

Hey! Stop deleting posts!!! lol... I just got done moving the other thread.

You've changed so many parts that you should be looking at the few that have been re-used. Is it possible that the distributor cap to rotor phasing is off and the wrong cylinder is receiving spark? Or maybe there's a problem with the coil? Is the distributor wiring laying on plug wiring anywhere? Is the pickup coil correct for the module (there are clockwise and CCW parts)? Did you re-use the balancer? Is it possible the outer ring is no longer in the correct position? Or is the balancer designed for a different timing cover and the mark is not lining up at TDC?

You should have tools to monitor what the computer is seeing and commanding. A scantool or a laptop with scan software and a cable will work. Check timing at the balancer against what the ecm is commanding. A simple spark test tool can give good indication if spark is constant and steady. Confirm the throttle body and injectors are correct for the engine displacement. If there's an EGR make sure it is not opening (this usually gives a sag without backfire, but it helps to check everything). It can be really tough to diagnose a vehicle over the 'net but sometimes with enough patience and persistence it can be done.

[Jeepcrazed]

Hey! Stop deleting posts!!! lol... I just got done moving the other thread.

You've changed so many parts that you should be looking at the few that have been re-used. Is it possible that the distributor cap to rotor phasing is off and the wrong cylinder is receiving spark? Or maybe there's a problem with the coil? Is the distributor wiring laying on plug wiring anywhere? Is the pickup coil correct for the module (there are clockwise and CCW parts)? Did you re-use the balancer? Is it possible the outer ring is no longer in the correct position? Or is the balancer designed for a different timing cover and the mark is not lining up at TDC?

You should have tools to monitor what the computer is seeing and commanding. A scantool or a laptop with scan software and a cable will work. Check timing at the balancer against what the ecm is commanding. A simple spark test tool can give good indication if spark is constant and steady. Confirm the throttle body and injectors are correct for the engine displacement. If there's an EGR make sure it is not opening (this usually gives a sag without backfire, but it helps to check everything). It can be really tough to diagnose a vehicle over the 'net but sometimes with enough patience and persistence it can be done.

Sorry for the confusion and thanks for cleaning up my mess! I should have elaborated a little further. This was a new long block and ALL sensors have been replaced with new ones, new injectors, dizzy, plugs, wires, EGR, etc. The only thing not "new" is the TBI assmebly (even though I've cleaned it twice to ensure it's good to go). I'll have to look into where to pick up a scantool or a cable/software to monitor with the laptop.

[1project2many]

No problem. We try to be low-stress here.

Well, you just eliminated a bunch more variables. You can use a timing light to watch the pattern from the injectors to ensure they're both firing consistently. You can also look at the top of the injectors under the electrical connector to see if the colored stripes are still visible (probably not). The stripes can be used to identify the injectors.

If you want an all new TB, I just found a kewl site two days ago...
http://www.oem-surplus.com/gmwp/gmc.htm

If you can find a TB that will fit your application you can't beat the prices.

[Jeepcrazed]

Already checked the injectors. All is good there. Just ordered a scantool. Should be here on Saturday. Thanks for the help so far!

[1project2many]

With so many parts replaced, and confidence that all the parts are good, it's gonna be tough. Plug wire routing can cause crossfire which pops n snorts. Swapping 5 n 7 wires is one of the most common SBC mistakes and it also causes pops n snaps. It can be hard to confirm injectors are truly good without specialized equipment although it is sometimes possible to rule out some very obvious problems. Are you using a 4bbl manifold and spacer under the TB? If so then a stock tune is not likely to work there. Auto trans calibrations on early ecm's are usually very different from manual and can cause driveability issues. If it were me I'd be watching spark with a scope, checking timing against commanded using a light, checking other scan tool values and comparing them to expected readings, and I'd be trying to watch mixture for signs of lean / rich using O2 readings.