90Iroc

Hey everyone, I've got one for ya... When I cruise at about 45 -50, my car bucks and jerks. The distributor is brand new, the coil is good, the wires are all alright, I'll check the injectors tomorrow, but I don't know what else could cause this. It happens at about 1500 RPM and also around 3000 RPM. It only does this when there is a load on the engine. In neutral it won't do it. What can I check/do? My car is a 1990 Iroc 305/ 5 spd with speed density, and an MSD 6A ignition system. Please HELP!!!

david roush

iTrader: (1)

Could be the injectors , i had the same problem too. But it only used to buck when i would cruise and let off the accelerator and coast, i'de push the clutch in and it would stop, turned out my prom was the cause of it.

DANIELEK

When my car did that my fuel pump went south a couple weeks later. It only happened under load too.

Once your pump dies you are screwed no matter where you are and replacing it is a pain in the A...

What is the mileage of your car?

90Iroc

The injectors all check out all right. Is there a test I can doto the PROM to see if it's indeed bad? It's an Ed Wright (Fastchips.com) chip. I guess I can just plug the stock chip in and see what happens. The fuel pump is good. It's about a year old. It's from a Syclone/Typhoon. Anything else that could be causing this? Oh and by the way, it happens any time I'm on the throttle lightly, very lightly. Not just at those RPM's. I thought it was those RPM's because those are my cruising speeds. But it will not do it in neutral. Any more ideas? Can a MAP sensor do something like this? What does the MAP sensor do? How about EGR? I just replaced it a year ago as well.

ULTM8Z

Was Wright's chip running ok before? It sounds to me like a throttle-tip in problem. You way need to adjust the Accelerator Enrichment vs Delta TPS table a little such that the ECM throws a little more fuel in when you open the throttle blades.

Just for kicks though, check your throttle position sensor. You should have at least .54 volts across the blue and black wires at closed throttle and about 4.5 to 5 volts at WOT. WIth the voltmeter on it, slowly open the blades and see that the voltage increases smoothly with the opening of the throttle. If you start seeing spikes or dips, your TPS is probably bad and should be replaced. Also, you should also have 5 volts across the gray and black wires at all times. The ECM sends out a 5 volt reference voltage on the gray wire. The TPS being nothing more than a potentiometer, drops that voltage down to a lower value based on how much the throttle is open. The ECM then reads that lower voltage on the blue wire, indicating how much throttle you're giving it.

The MAP sensor simply traslates internal manifold air pressure (or vacuum, depending on how you look at it) into a voltage signal which the ECM reads and makes an estimation of how much air is flowing into the engine. That sensor, combined with the TPS sensor tells the computer how much throttle you're giving the engine.

90Iroc

Last time I checked the TPS about nine months ago it was fine. I should really check it again though. The chip however I don't believe has ever given me problems before. The last time my car behaved something like this it was a couple of bad injectors, but they're fine. It's just frustrating. I'll let you know how the TPS goes. Thanks!!