Could it be something as simple as the ignition timing?

 

17 year old o2 sensor? Also I got a bad egr out of the box. Cleaned the old one put it back, works great!

 

i checked my timing with a scan tool and its bouncing around all over the place.....and its saying its in the negative too...

 

Normal for timing to jump around a bit, but it should never be ATDC (After Top Dead Center). What the scan tool shows is what the PCM is applying, not necessarily what the engine is utilizing. Check distributor cap & rotor, (use AC Delco only) check camshaft retard, and check for worn distributor bushings and or drive gear. Each one of these will affect how the engine utilizes what the PCM commands for ignition advance. If camshaft retard is off 10 degrees, so is ignition timing.

 

so if its BTDC it should have a plus sign next to the timing reading on the scan tool? and mine is jumping around like 25 degrees or so in minus mode. i have heard many 95's doing this too but dont know why. with in the last year i put a new ac delco distributor gear and cap and rotor. i also put the dist 1 tooth advanced and it would not start. then i retard 1 tooth and it would not start. all this and no change in the way it runs. then i had made a custom rotor to advance the timing mechanically and it ran better but the scan tool does not show the advance. im not sure how to check camshaft retard without pulling the timing cover and using the large degree wheel. is there another way to do it without all the disassembly? also do i have 2 computers? is it 1 under hood and 1 under the dash? and which controls the transmission? and how do i get rid of p700 and p1100 codes?

 

Lotta questions and to answer them correctly we need to know more about your vehicle. 1995 "W" engines used 3 different computer control systems and 2 different fuel delivery systems, (one of the reasons Oldsmobile did not produce the Bravada in 1995). Diagnostics are unique for each system. Since you're getting "P" codes, you don't have OBDI so that narrows down the possibilities. Do the spark plug wires attach to the distributor cap horizontally or vertical? This will determine if you have OBD1.5 or OBDII.

 

they attach horizontally, i hope that helps you know more about it and be able to shed some light on whats going on with it,please let meknow, thanks so much

 

Your engine is one of very few fully compliant OBDII systems that were installed in 1995. Your engine has CSFI, (Central Sequential Fuel Injection) not CPI/CMFI.

It depends how the scan tool was programmed to display ignition timing. If you're reading 25 degrees, it has to be BTDC, it wouldn't run at 25 degrees ATDC. The minus sign must be a "separator" or something.
See post #24.
Usually they will at least start, but may run poorly but, it will set DTC P1345 in memory and turn on the SES light.

The scan tool shows what the PCM is applying, not necessarily what the engine is actually utilizing, (you added or removed X degrees). Essentially you modified the ignition timing X number of degrees and the PCM had no way of "knowing" what you did, or even that you did anything. It just continued making adjustments trying to compensate for what you did. Not a good idea (next question will explain why/how).

This is a stock 4.3L engine, not NASCAR or NHRA No degree wheel or disassembly required. Camshaft retard is a rather misleading name for what it is. It perfectly aligns the camshaft position sensor to the camshaft, hence the name, camshaft position sensor. Ideally it should be zero degrees, (perfectly aligned with the camshaft) with a tolerance of + or - 2 degrees. When it is adjusted correctly: It aligns the rotor with the #1 cylinder terminal in the distributor cap, which reduces/prevents crossfire inside the cap.
The PCM uses the data from the camshaft position sensor, (along with data from the crankshaft position sensor) to accurately detect misfires and determine which cylinder(s) are misfiring. In a round about kind of way, camshaft retard is similar to "base timing", with an added twist. To adjust camshaft retard, the distributor is rotated. The hole in the lower intake manifold is slightly larger than the distributor housing, the "slop" allows the distributor to turn and will affect camshaft retard by ~15 total degrees. The distributor drive gear has 13 teeth, each tooth accounts for ~27 degrees of rotation: If camshaft retard is off by ~27 degrees or more, (one tooth off) in either direction, P1345 will set in memory and the SES light will come on. If you can not achieve zero degrees by rotating the distributor, the hold down bracket must be removed and a SBC, (small block chevy) hold down bracket, ($4) installed in its place. This will make the distributor fully adjustable. Camshaft retard is viewed on a capable scan tool. The el cheapo $400 or $500 jobbies can't access the data stream.

With the EDI system, the PCM "knows" when the rotor is aligned with each terminal in the cap: it calculates the desired advance, and tells the ignition module when to fire the ignition coil so the spark is delivered when the rotor is at the terminal... absolute minimum distance between the rotor segment and the cap terminal...no chance for crossfire. If camshaft retard is off, so is ignition timing.

One PCM, (Powertrain Control Module) (2 pieces) mounted on top of the coolant reservoir. The PCM controls transmission and engine. The BCM, (Body Control Module) is under the dash, just left of the ash tray.


It may have something to do with the adage "junk in, junk out" in computer jargon. If the engine is not supplying the transmission with smooth power, the transmission can not supply the drive axle with smooth power. The PCM may be interpreting the problem as a transmission problem. Take care of the engine "issues" and see what happens. that's the best I got on that one .... for now.

 

With a cheapo scan tool from here, as low as $50:
ScanTool.net LLC - Scan Tools, PC, iPhone, & Android based OBD-II (OBD2) Interfaces, OBD diagnostic software

And this software from here for your laptop with the GM enhanced add on $200: ScanTool.net LLC - ScanXL Professional - ScanTool.net

You can read, then adjust the Cam Retard PID as well as many other things.

 

will that work on OBD1?