Hello Everyone, my 1991 formula firebird 5.7 v8 has lost some power and is eating gas at a very high rate. I get 150-160 miles on a full tank. used to get 230-240. smells like its running rich. the idle gets low (below 500 rpm) at complete stops or slowing down. failing emissions is also a problem. The mechanics in the D.C area are a joke. i had to force the shop to hook up the obd1 because they repeatedly told me that "if the light isnt on then they cant pull the code". Well they tried and they were able to pull the code. After that i got the run around for 3 weeks so here i am trying to figure out the issue. car is in excellent shape otherwise. just hit 100k last month.

Any suggestions?
thanks

 

OK, code 43 is an ESC malfunction (knock detection & reporting system). If the SES/CEL was on all of the time from this error, that would do exactly as stated.

Kill power and mileage. But with it being intermittent, if often enough that is the issue. Check the knock sensor connector and wiring. Passenger side of block right above the pan rail.

Note that if the stock injectors are still in the engine, they need to go away...

RBob.

 

i chased this one for a long time - it was the combination of a lot of constant and intermittent stuff. - as it says its an ESC malfunction - but as i found out this is a potential 2 part issue between ignition and exhaust.

check the knock sensor wiring as RBob said
check the ground for the ecm which is usually on the back of the block on the passenger side.
Check the ignition coil
If it isnt those then go check the connectors on the module in the distributor, clean them/replace them
check the module itself (they are renowned for testing ok and actually being f'd) replace it if you can
if those check out run the test on the pickup coil - still not an exact science :/

**in lieu of testing all that crap above - grab a working distributor and see if that fixes it.**

depending on how long this has been going on you may have another problem with a plugged cat or muffler.

Testing is not that hard - drop the exhaust before the cat, wipe the plugs off, spray some starter fluid and see if she starts and runs.

When we pulled my cat we realised it was empty as someone had already hollowed it out. When when i dropped the rear muffler it hit the ground with so much force it would have taken me out had it hit me. whilst it wasnt a full blockage it was a partial blockage - enough to make the engine not start. It was full of this fine black soot from running rich for 5 million years of previous owners neglect.

i dont envy your position

 

AS Rbob has suggested, when code 43 is active, the ECM will default to full retard, to protect against detonation. This is about 28 degrees retarded from normal ET timing. The result is low power and terrible economy. Do you have a service manual for the car? You need to find the trouble tree for code 43 and follow it. Knock sensor failure is fairly common but connection and circuit issues on these cars at their age is also common.

As Rbob and zed have both suggested, as part of diagnosing code 43, you need to be sure the engine is in good working order aside from the ESC system. The OE injectors need to go if there is any fuel control issue. Check the FPR for a failed diaphram that may be feeding fuel through the vacuum line. Check EST timing control and overall condition of tune.

The ALDL connection is useful for alot more than reading codes. The ECM also provides live data that can tell a diagnostic technician alot about what the engine is doing. Unfortunately, as you are now learning first hand, diag. techs are rare today. What most shops call diagnosis is reading codes and replacing parts.

With engine running rich, it's a little odd that there is no O2 sensor code. I would like to see what O2 voltage is doing and what the fuel trims are across the engine's operating range. TPS voltage, ECT sensor accuracy. zed mention restricted exhaust. An exhaust backpressure test would confirm if this is the case. Of course, dropping the exhaust before the cat is one way to find out. This is easier on some models than on others. MAP sensor voltage reading high will also cause over fueling. This is a tricky one because the rich AFR will reduce idle vacuum and raise MAP voltage. Need to figure out what came first, the poor idle vacuum or the high MAP voltage. Test the sensor with a hand vacuum pump while watching MAP voltage on ECM data.

 

If starter was replaced, check knock sensor and connector for damage, corrosion and poor connection. Have seen many broken from improper stater removable. Check vacuum line to MAP sensor for collapsing with vacuum from engine running. Usually dry rotten vacuum hose, this will alter MAP readings.
Joe