Not running so good

[cee21]

Here is what it is doing. When I first start it up it will idol fine for the first 10 seconds then just fall on its face and almost die then rev back up. Then it will do it again a couple of times then die. If I just start it and take off in it, it will hesitate and jerk when I am trying to acclerate when I am just doing 0 to 15 and same as I shift into 2nd. I live in an apartment and have to drive slow the first 0.2 mi. But after it starts to get a little warm (the temp gauge starts to move) it will idol fine. But the valves will rattle like crazy after I push the pedal down about 1/3 of the way.

I checked the timing and it is good. If is a vaccum leak I have an idea where it is. All I did on the egr port was silicon up a piece of sheet metal and bolted it down. I have an egr simulator on it, just to let you all know. Does this sound like a vaccum leak? If so how big of a hole could it be that causes this? Could there be another reason for this?

[cgrey8]

It sounds like you are running lean to me.

What all is done to the motor as far as mods? Also is this carbed or EFI?

[jbaer619]

I had a problem like that a while ago and it just turned out to be a really bad ground on my fuel pump. To test this, pull the fuel line and turn the pump on, with mine it was just dribbleing out fuel when it should have had a pretty good stream.

[cee21]

I have a good ground on it, found that out trying to fix the fuel gauge. My brother turned the key off then on, nearly spraying me with liquid gold.

Chris, it is a mass air set up, but no mods expect for an imitaion K&N filter and L&L headers, versuses a stock stang. The motor is out of a 92 stang with an 89 harness and cpu. That is it. Wouldn't a vaccum leak cause it to run lean? I have a egr simulator on it, the thacometer stuff plugged up (but not to any vaccum, just to keep code from being thrown). The charcole canister is not plugged up though. I dont' have a check engine light wired up just yet.

[cgrey8]

On startup, that could easily cause lean-out. During startup, the EEC is running Open Loop and thus has only the MAF to tell it how much air is getting into the motor. If unmetered air is getting into the motor, the EEC won't know that and thus won't deliver enough fuel. Although it would have to be a fair amount of air since startup logic enriches the mix further than is really necessary. At least it seems to for my Explorer motor. But that's not to say stock GT motors with E7s don't need that enrichment. From what I've heard, the E7 heads are VERY intolerant of a lean mix. People have reported that their aftermarket heads and even the GT40p heads run well above 16:1 and even as high as 17:1 before the motor starts bucking lean at light cruising loads, but the E7s will begin bucking shortly after 15.5 or so which is just a little above stoic. In Closed Loop operation, the HEGOs will allow the AFRs as high as 15.0:1 as normal behavior. I can't imagine why they are so temperamental, but I've heard that from numerous people including a guy that has 2 early 90s Mustangs, one with the stock 5.0L, and another with an Explorer motor w/GT40p heads. That guy was experimenting with purposfully running his motor lean to get fuel economy benefits. He just forced OL all the time and setup his fuel tables to deliver lean mixes at cruise. He was confirming his AFRs via Wideband and drove the engine quite a while with 16+ AFRs to see if running it lean would help gas mileage. It didn't help enough for him to keep it this way since his plugs were showing a bad HOT lean condition, but I think he said it did pick up another MPG or two doing that.

But back to subject, 89-93 EECs will take anywhere from 60-100 seconds to go Closed Loop. There are 3 temperature ranges (cold, warm, and hot) that affect the time it takes to go CL. For some unknown reason, the Warm Time delay to enter CL is longer (100sec) than the cold or hot (60sec). There's also a control that depending on which of those 3 modes you crank in will require the EEC to see the HEGOs switch a certain number of times before entering CL. By default, a cold crank requires the HEGOs to switch 3 times if you startup cold, and 0 required for warm or hot starts. My suspicion is Ford's expectation is that the HEGOs would warm up, and stay rich for the rest of the crank preventing the EEC from seeing 3 HEGO switches and thus forcing OL for a bit longer to give the car longer to warm up. So with that thinking, the engine would stay Open Loop until the engine is warm enough to be considered "warm" which warm didn't require any HEGO switches and by that time, the startup delay has long since expired allowing the motor to go CL. Although even when I ran the stock values, I never saw it take more than the time limits. As HEGOs warm up, they will bounce a fair amount as they are warming...enough so that the EEC will see what it thinks are "switches" and it only has to drop below the threshold once and rise again before the 3 switch requirement is satisfied.

For my tune, I disable the HEGO switch count requirement and I've also lowered all 3 time periods to 32 seconds to enter CL. My setup runs far better in CL than OL, so I quicken CL as much as possible. Not to mention, it doesn't waste as much gas. I would enter CL immediately after crank, but the HEGOs do take a good 25-30 seconds from a cold crank to be responsive.