Can anyone give me any ideas what could be wrong with my tbi setup

[dalfy505]

I swapped a complete 94 tbi 350 and nv4500 from my daily driver when it was totaled into a 1973 k5 blazer. I replaced the chassis harness and added a painless tbi harness. After install engine fired right up and seems to idle fine. Now the but if I rev the engine it starts backfiring missing and dies or if I put it in gear and try to take off I get a loud backfire and engine dies. I replaced plugs wires cap rotor and distributor. No change in performance.
I was told to place a 3.9k ohm resistor in the adl to see if it was a mechanical or electrical problem and with the resistor In place the engine revs all the way up and I can drive the blazer with no problems.
So now I have no clue what sensor or electrical problem I have.
Currently useing ECM 16196396 azds as that was the one from the vehicle the combo came from also have a 1227747 and have tried that ECM and the same symptoms persist and the resistor seems to fix the prob

[carcaper]

From your symptoms it sounds like you have a lean misfire. Can you get closed loop and if so what is your fuel trims and O2 readings? If you swapped out the throttle body, are you sure you have the correct fuel injectors? I have ran into several occasions where wrong fuel injectors per application have these problems. One in particular I found 2.8 L injectors in a 5.7 engine. Needless to say that don't work to well. Do you have any other way to read exhaust readings? For instance a 5 gas analyzer or a wide band O2 sensor? Timing is also another factor you should consider, just make sure you have base timing set and make sure you have timing advance using a timing light monitoring the marks when you open the throttle off idle.

[dalfy505]

Nothing has been changed as far as the injectors or internals it's a bone stock 350 out of a 94 gmc Sierra my dad bought brand new in 94 with 4 miles on the odometer. I was given the truck and ended blowing a tire on the way to work and rolling it. After it removed the engine and trans and placed them in my 73. Never had any issues before the wreck and with a 3.9k ohm resistor in the a and b terminals of the adl it runs and drives like a champ.
Can you suggest a good hand held unit I can get real time info from my ECM

[lionelhutz]

What did you do with the emissions stuff? EGR valve?
Is your fuel pressure good? 13PSI?
Is the CEL on?
Did you make any changes like adding headers?

[dalfy505]

The original truck didn't have a smog pump or really any other smog stuff on it.
I did put headman headers, dual pipes with flow master mufflers

[dalfy505]

Egr valve is connected and seems to be working and not plugged if I squeeze the diaphragm and hold it it kills the engine

[lionelhutz]

The Painless harness isn't supposed to have any connectors for emission stuff so how is the EGR solenoid wired?

Where is the O2 sensor in the headers? Is it 1-wire or 3/4-wire?

[dalfy505]

maybe im wrong with what i thought was the egr. this is whats hooked up on the top left of the motor first the esc module then another sensor getting vacum from the tbi, it has a vacum port goint to a round diaphram on the intake and another port above that, then behind that the map sensor, and on the tbi the iac and tps are also connected

[Woods]

3.9k ohm resistor in the a and b terminals of the adl it runs and drives like a champ.

This probably is of no help. but here is a page explaining what this process does. 3.9 backup state, ignores the Map sensor.
http://books.google.com/books?id=CUg...minals&f=false

[dalfy505]

actualy was a help i knew it disabled some sensor just didnt know wich now i will replace my map sensor and check again. and to the earlier coment the o2 sensor is a 1 wire unit

[lionelhutz]

So the vacuum solenoid running the EGR is connected electrically or not?

Try actually answering the questions. Where is the O2 sensor?

[dalfy505]

yes vacum solenoid is running egr and is connected electricaly.
o2 sensor is located in the passenger header collecter
my bad lionelhutz just spaced out to answer that tried uploading a pic of my setup but haveing trouble

[carcaper]

The reason it runs better because you are putting the system in back-up mode. This defaults the system to basic fuel and timing parameters which by-pass all closed loop controls. This tells you that when the ecm is in closed loop thats its trying to correct for something it doesn't like. For that particular year I prefer the snap-on red brick scan tool. You should look at fuel trims and oxygen sensor to find out where you are and if the oxygen sensor is even working. To find out if the o2 is functional, monitor the voltage on the o2 pid and pull a large vacuum hose off such as the brake booster hose. You should see a major drop in voltage and then when you plug it back in you should see a major increase in voltage. That is of course if you aren't lean before you pull the hose off. This will give you a starting point in determining if the problem is basic or technical. Other things to consider are engine condition and a simple vacuum guage can help you check the engines ability to pump air. You should have at least 12-15 inches of cranking vacuum and go up to 17-18 at idle. Since you are saying the engine is running good in back-up fuel that would be the time to check it. When cranking the engine, listen for an even smooth sound and look at the vac guage for uneven or bouncing needle. If the needle bounces erratically you could have an internal problem with the engine. If its smooth and normal you know the engine is capable. Can't stress enough about the ignition timing, use a timing light and monitor the timing marks when the engine is acting up, you shouldn't see any erratic jumping of the timing. If you do, put the system in back up mode again and if then its normal, you need to find out why. Check all your ground connections and try unplugging the alternator. Computers and electronics do not like AC voltage, if you have a volt meter that will measure RMS, check the for stray AC voltage at the ALDL with the engine running with everything turned on, you shouldn't have more than 1/2 volt or .5 volt. Good luck in your venture.

[lionelhutz]

Well, the 1-wire O2 in your header collector is your first problem. That simply doesn't work right. You'll have to get that fixed. I'd recommend changing to a 4-wire. If your harness used the proper stock wire colors then it will have a tan wire that comes from pin D6 on the ECM and went to a eyelet that was bolted to the engine. Don't hook this wire to the block but instead hook it to the O2 sensor. This will eliminate the connections through the engine block from being a source of possible sensor issues. It gives a much better and more direct O2 signal right to the ECM. It used to be that the 4-wire O2 sensors were the most expensive but they're rather cheap these days.

You could use a sensor from say a '95 F-body. The wires will match the connector terminals as such;
A - O2 sensor ground - hook to the tan wire mentioned above
B - O2 sensor signal - hook to the purple wire that went to the 1-wire O2 sensor
C - heater - hook to ground
D - heater - hook to a switch 12V source

[dalfy505]

thanks carcaper will get that checked out and post what results i get. Lionelhutz i will wire one in and see what happens i orignaly bought a 4 wire but didnt hook it up cause the harness only had one wire but after hearing what you had to say i will swap it out