Hello everyone! Just wanted to pick your minds on a few issues I have been having with my 94' Lt1 coupe. I found a few things early on, but I still have a couple of them to sort out.... I have been having a misfire/backfire/stumbling issue since I bought my car in April. I found a lazy O2 sensor and a cross firing plug wire, replaced those and it seemed to help for a little while. I had a miss in one (or more cylinders) and tried un plugging the Injectors one at a time, take in mind that at first, you could hear the injectors pulsing (stethoscope) once they were unplugged- no difference, and once I plugged them back in, no pulsing sounds at all.now this was only on a few injectors, and I plan to buy a set of the Bosch III's from John at FIC anyway. I purchased an OTC Pathfinder OBD1 scanner setup yesterday, and plugged it in, started checking everything over, O2 sensors are performing well, coolant temp sensor was just replaced, right on the money there with regards to temps. Injectors show the same readings across the board, can't remember what it said, sorry, i'll record everything tonight and post it all tomorrow. but one thing that caught my eye was, while checking the diagnostics, it said no codes stored, yet I get a message that says Maf sensor possible short, bad connection and the very next thing I see is Injector faults, possible shorts or bad PCM. I know these cars have Vats, and I have the correct key or I would have had many more issues and not be driving it today if that was the case. Let's say just for arguement sake, I need to replace the PCM, am I going to have this "Flashed" at the dealership to enter my VIN into the PCM? (worst case scenario) I really doubt it's the PCM, but it has happened to others from what I have been reading. is there a test I can do to prove my MAF is good? (I just ordered a FSM, and it should be here this week, but until then, I'm stuck......as always, thanks in advance!
Ben Smith

 

Take a datalog of your maf reading with the engine running and then examine it to make sure it is reading properly and consistently. Need a datalogger such as tunerpro software and a PC though and an aldl cable from Moates.

 

Lemme,
I'll have to get that stuff when I can, I'm going on Vacation and it will have to wait until I return. The Injector problem seems to have increased the coolant temps as well, guess without the fuel entering the combustion chamber is causing it to run lean and adding to my problems. any ideas on how I should test this Maf?
Thanks!
Ben

 

Since you're wondering about a bad MAF and/or bad ECM,,,unplug both, clean the contacts on each connector, and plug back in. Disconnect the battery to reset error codes and retry.

You may find that something as simple as a deteriorating connection might be your problem. I have had at least two connectors in my 89 where I have "cured" faulty operation of the plugged in component thru simple cleaning of its plug contacts. (MAF and A/C head)

 

Gregg,
Thanks for the input. I'll try that this evening as well as checking the notorius grounds on the engine harness, just to make sure. these cars sure keep you on your toes, that's for sure! I really don't like wrenching on my own cars, but with dealer costs as they are, sometimes it pays to be persistant! I enjoy a good challenge from time to time.although, electrical isn't my best system to troubleshoot, I've solved a number of gremlins in the past. I've learned sometimes it's best to have another set of eye's look the problem over. Thanks again for the advice, I'll look it over tonight.
Have a good one!
Ben Smith

 

The MAF puts out a DC voltage level dependant on the air mass flowing through it.



By looking at the trace of MAF grams/sec on the datalogger any erratic signals should show up. Or it may just not give the g/s (and hence voltage output) it should.

A cheaper way would be to measure the voltage out with a cheap $5 digital volt meter and see if the MAF voltage reading fluctuates.

 

Thanks Guy's!
I was all set to dive in last night, but I got de-railed by S.W.M.B.O....
and before you all ask what that means, (She Who Must Be Obeyed) and her evil plans to renovate her daughter's Bathroom......so much for my plans....ROTFLMAO. I'll try and set aside some time to record all the parameter's and reading's I get of my scanner and post tomorrow, providing I don't get sidetracked,(yeah right). Thanks for all the helpful input, we will see what this does.....
Have a good One!
Ben

 

Is it possible to get a graph like that with a scan done by Tunerpro RT? I've got some scans done. But when you graph the MAF grams/sec. It only shows the grams/sec. It doesn't also have the volts.

 

The graph I have shown is how the ecm converts the maf voltage signal to the g/s you see on the datalog. There is a table in the arap bin viewable in tunerpro RT which has these conversion values. I just graphed the table in excel to make it easier to see what the computer was doing.