My 93 6 speed, 55000 miles, has a problem If the throttle is nursed it runs ok, but if I step on the gas to about 1/3 throttle, it bogs down and there is some pre-ignition pinging. It still goes forwardbut at a greatly reduced rate of acceleration. So far I have replaced the fuel filter, plugs, half the wires (the passenger (easy to do) side) and cleaned the MAF. A fuel pressure test shows 39 lbs fuel pressure idling and 45 while driving. A vacuum test to the fuel pressure regulator showed immediate drop in pressure and the manual said replace, which I did. The ignition module also showed faulty so it was replaced. There is a slight miss when idling and the problem seems to get worse as the motor warms up. The bogging down is also more pronounced in the higher gears. The service engine light does not come on. I have a new opti-spark and water pump but I am hesitant to do major surgery just to find out that isn't the problem. At any rate, I'm tired of stimulating the economy by buying parts that are supposed to be bad but the replacements don't help, either. Any suggestions? Thanks for the advice in advance.

 

O2 sensors??? Dave

 

We put the OBD 1 on it. There were no codes but the readouts said the MAP sensor was marginal. Nothing else tested bad. I think that included the O2 sensors. Replaced the MAP. No go. All the injectors are well within tolerance. Put on a new coil. Once again, no help. I did discover for sure, though, that it runs fine until it gets to operating temperature. Then it pings and is real sluggish accelerating. Backing off on the throttle and just idling down the road it runs ok, but step on the throttle and BLAAAAAAH ping ping ping. Since winter is setting in, I don't think I'm going to be using it more than once or twice before it's put away. If it doesn't get too cold, I may at least tear it apart this fall and put it back together next spring. Or maybe wait. I'm really getting sick of it, actually. Nobody around here knows a thing about LT-1s anyway. But thanks for the suggestion.

 

Yeah, the problem is in o2 sensors.

 

Thanks for the inputs. The car is put to bed for the winter, but I will certainly change the O2 sensors and see what happens. It does make sense now that I think about it.

 

Check the operation of the EGR valve. if the valve is not opening, it will cause detonation, which will cause the ECM to retard timing to compensate.

 

Hey, Mech, I was waiting for your input. How do I check the EGR valve?

 

pinging is a symptom of low octain fuel or high compression or timing advancde very high, 02 sensors normally cause a poping much like a backfire . mine was poping & surging on ocassion but never showed a code about two months ago it started doing this all the time replaced the 02 sensor & have not had a problem since & went from 325- 350 miles to the tank to 450-500 miles to the tank

 

1st, does your EGR have a wiring connector or a vacuum hose going to it. More than likely it has a vacuum hose. You can use a hand vacuum pump to open it while engine is idling and if it causes the engine to die or almost die it is working, also the vacuum pump will hold vacuum. The EGR with the wiring connector is a linear valve and will set a code.

 

poor car... maybe the one who did it dude is mad at you.