Howdy from San Jose, Ca
I just bough a 85' TPI automatic with a 52mm throttle body, headers, full exhuast(true duels)smog pump delete,no cats.
The problem that im having is very weird hesitation.
On a cold start it will idle fine but as soon as you give it allitle gas it will bog down ,pop up the intake and act very lean. If you floor it itll take off like a bat outta hell. But as soon as you get to the 1/4-1/2 throttle position again it bogs back down again,acting as if its gonna die.
When it warms up the hesitation gets less severe but changes sometimes too. Sometimes I can be driving and it runs PERFECT. But sometimes this weird thing happens. Lets say your cruising at 40mph in O/D. If I let off the gas then slowly apply it again it seems that it will not respond for the first second or two then itll kinda slowly respond back to life and cruise normal again. Also it kind of comes in and out of the hesitation as if its electrical,Kind of like itll hit a switch and run perfect again. Again if you floor it there is no hesitation and it takes off like a bat outta hell.
Has code 34,54 in computer
Fuel pressure is in specs throught all driving conditions(even when the hesitation is happening
TPS is set and is smooth the entire range(no drops)
Timing is set
CTS is withing specs throught the entire temp range
MAF has a good reading throught range (disconnecting MAF doesnt help the hesitation)
car does not have any vacuum leaks (I tested this the most)
egr is working properly
O2 sensor is very responsive (and new)
im beginning to think this is a computer problem due to the fact that itll run perfect sometimes then *blink* here is the hesitation again.
Thanks for any thoughts or help
pat

 

Do the pcm/ecm....whchever its called wear out? My cars electrical is pretty stupid. Clean out the throttle body? Fuel filter?

 

This is basic, but did you disconnect the timing connector, then set the timing? What is your timing set on? 34 MAF code can be caused by IAC being stuck, have you checked power and grounds to the MAF? What kind of grams per second air flow do you have at idle?

 

yes I disconnected the little spout style connector and set it at 6*,I tried 2,4,6,8,10* it pings allitle bit under hard accel when its at 10 but the hesitation still randomly happens. The weirdest part is that randomly it doesnt happen at all and drives completly normal , then its almost like a switch gets turned on.
Does anybody know of any good ways to check the circuit board of the pcm? could I open it up while driving and spray something cold on it for a test? or should I get slam it with a HUGE hammer...lol
thanks
pat

 

What kind of readings are you referring to? If you have access to a scan tool, give me GPS (Grams Per Second) @ idle.

 

Have you also cleared those 2 codes and they keep coming back?[8D]

 

Code 54 for the fuel pump circuit means the ECM has not seen a voltage supply on the circuit out of the fuel pump relay for the fuel pump. Does your car also have cranking issues, like extended crank times? Most GM's have a redundant power supply to the fuel pump via pump relay and an oil pressure switch. If the relay fails, the car will still run via oil pressure switch, but a sign of that is extended crank times while waiting for oil pressure to to activate switch.

 

thanks guys for the replys
I dont have a scan tool, I kinda judged the readings off of Hz, but It seemed pretty smooth and reacted as I would expect of higher air flow(higher frequecy at more airflow)
also found intermitantly the maf is losing its 12v source voltage.
Anybody got any wiring diagrams for the MAF circuit? I have a feeling ive got a ****ty relay somewhere..

Thanks guys

 

The MAF gets it's supply voltage from the fuel pump relay, I think. I will verify and get back to you. That might explain your fuel pump codes. You might not notice any problems with fuel pump because the pump supply voltage has a redundant supply through the oil pressure switch. A sure sign of that problem is extended crank times. [8D]

 

mech
thank you soo much for your help,

Definetley have very normal start conditions. Takes about a half second before it fires while cranking. Im finding more and more weird stuff about this car every day I check things out. Somebody did a hackjob on allot of this wiring.
back to the point.
Does anyone have a wiring diagram for the maf circuit? Im intermitantly losing my 12v source voltage to the maf sensor. Does the "controller" to the 12v maf sensor source control anmything else?

(on a side note, WOW THIS THING IS FUN TO DRIVE)
pat