Rough Idle/ Cutting out.. Ideas?

[dnguyen1963]

Actually the dme will see a voltage change and increase injector duty cycle to compensate for the added load. Thus making a lean running condition better due to more fuel.

Up to a point...more fuel without the increase in air intake would flood out the system. I think Jim's explanation is more plausible. But then again, you both might be correct. The engine will probably try to do both to achieve the best fuel/air ratio. Thanks for the explanations.

[andrewm]

EH is more on point, all in all, it dumps fuel by resorting back to a safety/base map. Vehicles can operating on a VERY heavy air fuel ratio. Cars can run with a 8:1 or under for the air/fuel ratio.

I do get the feeling there's a vac leak, but it just doesnt add up. It only stalls when the car has been running for a while, and traffic seems to make it worse. No high idle, no sounds of vav leaks, car operating amazing until this. Weirdest vacuum leak, ever.

I'm gonna swap out the MAF tonight to see if anything changes, and might actually swap the DME just to see - I've got the MARKD chip so it's gonna be a tough transition ha.

[EH Motorsports]

Would also check and clean the coolant temp sensor for the DME. And make sure the connector/pins are making a good contact. One way to check the pins is to do a pin drag test. If a paper clip or staple (depending on pin size) feels like its dragging then the pins are good. If the clip/staple falls out of the connector then you may need to think about re pinning the connector or a new connector all together.

If you haven't already I would just clean all the connectors to the sensors and engine harness. You may even want to pick up some dielectric (tune up) grease and apply it to the connectors.

Reason being ive seen many 20 plus year cars start having corrosion issues and causing sporadic running problems. If resistance increases it can fool the dme into thinking the car is still cold or hot and add an incorrect amount of fuel correction. Also when temps increase resistance does as well.

[andrewm]

thermal agitation is one of my fears, the harness is in better shape than I would have imagined, but there are certainly some worn sensors. I'll take a look at the essentials. I've been trying to get a shop here to call me back about a smoke test, hopefully this weekend I will be able to put some hours in on this.

[603Racing]

Subscribed... interested in results.

[andrewm]

I figured it out. I did a lot of driving and idling yesterday, trafficing and yeilded no issues.

I replaced the lift pump. The tank was clean as a whistle, the strainer looked pretty clean as well. Wiring all good. Then it dawned on me what was happening.

The lift pump was failing, and when I turned the lights on the altenator cranked out more juice - causing both fuel pumps to generate a little more juice.

Luckily, I had a spare lift pump laying around.

[andrewm]

Scratch that - happened again. Gonna try swapping a few parts over from the parts car...

[603Racing]

I was having similar issues where my car would only "act funny" at random. Turned out to be the round electrical connector under the intake being corroded in addition to a vacuum leak. A lot of important functions run through that connector.

[andrewm]

yea...did you replace the whole harness? or just need to clean it up?

[603Racing]

I have just cleaned it up for now. I will be doing a more permanent repair soon. I have yet to be able to find that connector part number.

Simply cleaning it with some spray cleaner and an air hose made a big difference.

[andrewm]

If memory services, that thing is a pain to get to...did you have to take the intake manifold off?

[Quinthirty]

While you're at it, you can also check the relay connections of the fuel pump relay. As you've mentioned, 20+ years is a long time. I remember cleaning it and it made a whole lot of difference. Be careful about the "relay locks" though. They're very brittle. Once you break it, you need to replace it. Otherwise, the sockets can "slip off" and the car can just die while your cruising on the highway. I think its around $6 each.

[603Racing]

If memory services, that thing is a pain to get to...did you have to take the intake manifold off?

No, you can get to it without taking anything off. However, it is easier to get to if you take the airbox and intake elbow out. I cleaned mine with the airbox still in the car... in hindsight would have been much easier with it out.

[andrewm]

Awesome! I've actually got the airbox off since I'm doing my 5 speed swap. I will try it this weekend, I'm about 90% done with the swap so hopefully I can finish it with what little time I can spare this weekend.