Use a DVOM to monitor MAP sensor voltage. Should be about 1.2-1.6 at warm idle and should hit 4.5 at WOT. Because the MAP will respond dramatically to changes in manifold pressure, it can be hard to pinpoint a MAP sensor with an in range failure by monitoring engine running MAP voltage. Testing the MAP with a vacuum pump will reveal a glitch. The code 34 you have seen may be a sign that the ECM has seen the MAP be out of range at certain times. The only sure way I know of to eliminate a faulty MAP sensor is to swap in a known good part and look for an improvement. I always keep a known good GM MAP sensor on the shelf for just this purpose.

 

 

Tested the map sensor. At warm idle its reading 1.3v. At 2000RPM it read 2.0 volts. With key one engine off it read 4.5 volts. Tested the 5V reference wire and it had 5 volts like it should. With key off, i disconnected the map sensor connecter. Put a jumper between terminals b & c. Turned key on. Voltage reading was 4.9 Volts. Got the same voltage reading when i plugged the sensor in with b & c jumped. So, according to the flow chart, I have a bad sensor or pigtail to the connector?

I also hooked the fuel pressure tester back up to it. Key on engine off it read 43psi. Cranking pressure was 40psi and running pressure was 38 PSI. With key on engine off, the pressure would go to 43psi then quickly bleed down to about 30 psi. It would then hold at 30psi, and continue to bleed down after a while. Shouldn't it hold 43psi for hours? Some one had put a fuel pump in it at one time. they did the cut a hole in the floor tick to change it.

When the car is started cold, it will not idle, instantly dies now. You have to keep you foot on the gas for a couple of minuets. It will then idle, but very low, about 500 RPMs. It has not done this before until now.

 

The bleed off is too quick. It may be the regulator, the check valve in the pump, or an injector. You need to complete the testing to pinpoint which it is. Your MAP test results look suspicious. The engine running and key off readings all look normal. This couldn't be if there were an open ground or signal circuit, as your jumper tests would seem to suggest. Are you sure you had good contact with the jumper between pins B&C? Are you sure that you weren't jumping pins A&B? The reading of basically full reference voltage would certainly suggest this.

Looking into the thinking of the engineers in developing the steps of the trouble tree, we can see that pin A is the 5v reference, pin B is the signal to the ECM, and pin C is ground. Therefore, jumping pin B to pin C should produce a signal near zero volts. If it reads near 5 volts, this would suggest an open signal circuit(an open signal circuit will read 5 volts at the ECM side because of the diagnostic resistor in the ECM), or an open ground circuit. But I tend to believe what I see on data stream or backprobing at the sensor. And your readings in this area were normal. I would want to repeat your tests to verify your readings before replace the MAP. I would definitely be taking a look at your fuel system. You may be looking at an injector issue.

Code 34 will set due to unusually high manifold pressure, such as caused by a really poor idle. I have also seen code 34 on engines with a stalling problem.

 

I retested the map. On my connector the ground is Labeled Pin A, so when I tied B & C together I was getting the reference voltage. I retested The two pins using the two correct pins this time. I was getting 50MV, I i believe the problem is not in the map sensor.

Now for the fuel system. The pressure regulator diafram is new, and has no fuel in the vacume line when pulled. I also just replaced the fuel injectors with a set of Bosch II's from Southbay Fuel injectors . After cycling the key a couple of times I pulled the plugs and they are dry. That leads me to the pump. Like I said its been replaced at some point due to the hole in the floor right above the pump. As for what pump they used in it I have know idea. It hasn't been changed that reciently. The top of the sending unit is caked in gravel dust, etc.

 

When its cold, it seems to run ok. When it starts to warm up it starts doing is thing. I think the car is running really rich. Has a gassy smell when warmed up. What about the IAT sensor screwed into the bottom of the plenum? Could that also make the mixture way off? I may have to break down and buy a ALDL cable and log this thing.

 

The mat could cause rich or lean conditions and is the same part number as the cts thermistor.

 

You could test it bye disconnecting the 2 wire connection at the back of the plenum after the engine is warm. If you have a infrared heat gun you can air it into the plenum at the mat to see the temperature and compare to this chart.

 

Thanks I will test it out. I picked up an aldl cable and a cheep laptop off ebay. I'm going to try a different approach and log it with winaldl. Hopefully that will yield some results. I'm just grabbing at straws at this point.

 

Just read through the thread and watched the video you threw up. Where exactly was your flatspot? The only area in which I found to be needing correction in the video was during deceleration when you let go of the throttle, the air/fuel ratio is getting skewed and the engine momentarily wants to stall, and that can be because a number reasons in itself. If your injectors aren't leaking, and if you have no vacuum leaks, and the IAC/TPS & Idle Screw are set accordingly, you shouldn't have that problem when in Closed Loop. Was that the only problem you were looking to fix, the misfire after deceleration?

 

Win aldl does not support the 1227730 . Look into tunerpro and there is a thread here bye Saar for a cheap USB converter.

 

https://www.thirdgen.org/forums/diy-...converter.html

 

I let go of the gas when it hit the flat spot and started chugging.

 

possibly a bad ecm

 

Have you tested you injectors. Low resistance or shorts sometimes occurs when the engine gets hot. Measure the resistance of each injector. Should be around 16 Ohms I believe.

 

Covered in Post #4

 

As soon as I get my ALDL cable and tunerpro RT set up, hopefully we can put this old dog to bed.

 

you have replaced everything but the mat and ecm.

 

oh and map, if your close to a junk yard you can pick up a couple for cheap. Look for the number 466 on the top of the map.

 

Okay I data logged the car today with tunerpro RT version 5. I have included the files here. Can some one take a look at them and tell me what they think? Thanks.

 

ur files are not valid,what did u use to create them/datalog?

 

I screwed up the data log file types. There are the actual data logs from Protuner RT 5. I am trying to figure out how to make the logs into a readable text file.

 

Okay, I finally got it to export into a readable text files, and they are included in this post.

 

do you have a graph that you could post that show int and blm as well when the event occurs ?

https://www.thirdgen.org/forums/diy-...e-but-blm.html

 

Am I really seeing 34-50 degrees knock retard? That doesn't even seem possible.

 

Here is the graph. The top line on the graph is BLM and the bottom line is INT. I captured it at the spot where it does it thing.

 

I see zero knock retard when I just looked at it?

 

I have been thinking quite a bit about this for a couple of days. Could A bad ground cause all of this? The last couple of times I've cold started the car, The computer commands a 1000 RPM idle and the IAC is pegged at 160, but it won't idle unless you hold your foot on the gas for a couple of minuets. Once it did idle it was really low (500 RPM or lower).

Before I started it this morning, I wiggled the ground strap at the rear of the passenger side head. I did the same for the grounds on the rear of the drivers side head. Started it and it went to high idle like it should, and IAC count was in the 20's. Ran fine for a few minuets then started doing its thing again.

 

I see knock count zero, knock retard 34+ degrees. This will cause the engine to barely run.

 

Poor ground connections will cause serious issues. Definitely verify that all connections are clean and tight. Looking at your BLM, INT graph, I see the ECM pulling out fuel in response to a perceived slight rich condition. BLM starts at 130 which is on the lean side of the neutral 128. Then works its way to 125 which is going toward the rich side as if it sees too much fuel and is trying to lean the system out a little. Neither 130 or 125 are seriously out of whack. Either way you're still within 3 points of neutral. INT seems to track normally as it drives BLM from 130 to 125. I would be concerned if I saw INT go low or high and hang there. INT of course is short term fuel correction and reflects the trend of O2 voltage, whether it is tending high(rich) or low(lean). BLM is long term fuel trim and reflects the trend of INT. As the engine warms, it is normal to see the fuel trims start slightly lean or rich and move toward neutral in response to the decay of warm up enrichment.

 

Im seeing MAP Kpa at 34? *shrug*. The car does have a shiny new knock sensor on it. The previous owner must have put one on. What about the two dips in the graph when INT went down to 117 but BLM stays at 130? Is the the computer trying to correct for the engines bad behavior? I will take the gounds off tomorrow and check them out. They make me suspicous after wiggling them and then all of a sudden the cold high idle problem that popped up while figuring this thing out went away.

 

I didn't see the knock retard as well?

 

Of course. I apologize for the my confusion. I was misreading the data. As far as INT and BLM go, as INT fell to 117, BLM came down to 130, then INT began to climb again. Each time INT goes low, BLM responds by lowering as well. At the end of the graph, INT is climbing again. That is pretty much what I expect to see these do. It seems normal to me.

 

I just reviewed this thread from the beginning to refresh my memory of your car's issue. Have you verified cranking compression? Also, because I have seen too many ignition issue that looked like fuel system issues, I would like to see you put this engine on an ignition scope to verify stable timing and KV. I have seen several cases where a MAP code was set due to another issue that caused the engine's manifold absolute pressure to be out of whack.

 

I think I may have solved the problem. I took the gound cables off the heads and battery. Cleaned them all, and checked the connections of the ends. Put them back on, and so far it seems to be running like it should. I drove it to work today, about a 60 mile round trip, and it made it there and back. I did log the car while I drove it.

I was reviewing the log, and the 02 sensor volts looks werid, up and down. Werid to me anyway. I have included a graph of it. The sample is during driving on the highway. The readings could be normal for all I know?

 

maybe a screen save would be easier on my eyes

 

Lol. You will get used to seeing this my freind. As I said, INT follows the "trend" of the O2, whether it tends low or high. 02 voltage, on a narrow band O2, will constantly toggle when in closed loop. The O2 reads oxygen content in the exhaust stream and the ECM responds to O2 voltage by increasing or decreasing injector pulsewidth. In a perfect world, injector ontime and O2 voltage would be steady as they walk hand in hand. This is not a perfect world so the two run back and forth chasing each other. INT is the ECM's short term correction factor for changes in engine load, throttle position, etc to try to keep the O2 sensor toggling around .450 volts. BLM is long term correction for changes in the engine. What I see in your datalog is normal, healthy O2 function. Awesome news on the repair! Happy motoring.

Normal range for a narrow band O2 sensor in closed loop is 200-800 milivolts. Expect it to spike as high as 950 on throttle snap and dip as low as 100 on decel fuel cutoff. O2 voltage should switch from low to high about 15-20 times per second at 2,500 rpm.

 

It was one hell of a ride, but I think we finally got this thing whipped into shape. Thanks ASE doc and everyone else for the help. I can stop pulling my hair out now, lol.

 

Any progress?