What happens at startup?

redcoupe86 · 03-31-2006, 03:43 PM

Im trying to diagnose a problem that i am having, however, even though i have the Bentley, i didn't see a comprehensive "flow diagram" of what happens when you start your car until it warms up. What Im looking for is a step by step diagram that follows which sensors, components, circuits, ect. come on line and when. This would help me focus in on the relevant instead of spending my time chasing dead ends.

I actully have few day old post on my issue, and I have begun looking at various items. All so far check out.

Without getting too much into it. My car has been getting harder to start, not in the sense that it doesn't crank right up, it does. However the idle has been getting rougher each time (say ove the past 15 starts - within a weeks time) and its not a smooth turn over when the engine ignites. Just the other day it starting hunting beteen 800 rpm and 1800 rpm and bucked between gearshifts.

I've tested most the resistance checks you can get to in the engine compartment, and all pan out. My ICV is good, my wires, cap and rotor are new, so are the plugs.

I have not tested the CHT or the flywheel sensors yet.

I've tested the resistance of pin #1 and #4 of the AFM and it came out ok. I have it off the car now. Is there a visual check one can do to it to see anything or any other check while i have it off the car?

The only thing i found, was when i was checking for vacuum leaks the fuel pressure damper vacuum line was bearly on. However, even if this vacuum line had come off, I doubt it would cause the issues i was having - esp. the bucking.

I've orderd a DME, so that will be installed as soon as I get it.

randywebb · 03-31-2006, 04:15 PM

what happens on my car is I shoot some raw fuel down the hole and the 'lectrickery blows the sucka up...

- you might want to remind other posters that you have a DME system... also this info might be in the yellow Bosch theory of operation booklets.

CliffBrown · 03-31-2006, 04:54 PM

Might want to make sure there's no water in the fuel.

redcoupe86 · 04-01-2006, 08:01 AM

Quote:

Originally posted by CliffBrown
Might want to make sure there's no water in the fuel.

how do you do that?

Zeke · 04-01-2006, 08:17 AM

Well, you could remove the filter and open it. If it's time to replace, that's not a bad thing.

Don't overlook the real simple things like spark plugs, although they do go away more slowly than you indicate. The point is, before you go after things like the flywheel sensor, make sure the basics are in order, like ground connections (not that has anything to do with a hard start, just an example).

Do you drive this car fairly hard from time to time? Maybe you'd want to consider using a bottle of Techron just to clean things up a bit, like injectors, etc. Can't hurt, that I know of, but I agree, no substitute for knowing exactly what is going on at each step.

redcoupe86 · 04-01-2006, 08:32 AM

I drive the car about once once or twice a week, however, prior (or at least i think prior) to this all starting the car did sit about a month so i could work on the front suspension.

WydRyd · 02:40 PM

Disconnect the CHT sensor at the harness near the left plenum and check to see if it's a one wire or dual wire sensor. If single wire, you really should upgrade it. Measure the resistance to ground and it should be between 2k - 3k OHMS.

BTW, my car was bucking quite badly too, and I found the issue was the AFM, even after I had measured outputs at the flapper's various deflection points. Try to borrow a good AFM and replace it for a test run. If it resolves your issues, then the AFM is the culprit.

My guess would be CHT sensor or AFM.

If your Damper was screwed, it'd be dumping excess fuel into the intake via the vacuum line and you'll be seeing heaps of smoke out the exhaust. It's worth pulling it out and just blowing air through the fuel port and seeing if any air escapes through the vacuum port.

Just some ideas

P.S: BTW, does it only do this when cold, or irrespective of operating temp?

redcoupe86 · 04-01-2006, 03:32 PM

Quote:

Originally posted by WydRyd
Disconnect the CHT sensor at the harness near the left plenum and check to see if it's a one wire or dual wire sensor. If single wire, you really should upgrade it. Measure the resistance to ground and it should be between 2k - 3k OHMS.

BTW, my car was bucking quite badly too, and I found the issue was the AFM, even after I had measured outputs at the flapper's various deflection points. Try to borrow a good AFM and replace it for a test run. If it resolves your issues, then the AFM is the culprit.

My guess would be CHT sensor or AFM.

If your Damper was screwed, it'd be dumping excess fuel into the intake via the vacuum line and you'll be seeing heaps of smoke out the exhaust. It's worth pulling it out and just blowing air through the fuel port and seeing if any air escapes through the vacuum port.

Just some ideas

P.S: BTW, does it only do this when cold, or irrespective of operating temp?

I have the new 2 wire, and though i don't see it in the PO's receipts, it looks relatively new - mot as grimey as the rest of the stuff around it. I tested the the resistance of the CHT and it turned out in range. Though this only proves it should work, not that is necessarily does.

The only issue with the damper was the vacuum line was barly attached.

This only seems to happen when its cold. Right at start up, until it warms up.

redcoupe86 · 04-01-2006, 07:47 PM

With the multitude of posts on idle mixture and such I have not been able to find the post I say a while back about how to set your idle mixture by using some reading from your O2, would anybody have a post to a detailed link?

Joe Bob · Joe Bob's Garage

Any tuning that involves mixture needs a smog testers probe and scope. You can get "close" with in dash gauges as long as you have CHT, EGT and A/F gauges......

jester911 · jester911's Garage

I chased a similar problem for over a year. I finally fixed it.

See this link. Finally...problem solved, hesitation etc

stlrj · 04-02-2006, 06:02 PM

Your intake manifolds might be loose resulting in vacuum leaks.

WydRyd · 04-02-2006, 07:25 PM

Might very well be a vaccum leak. As the engine warms up and things begin to expand, the vacuum leak might close up and the symptoms aren't as pronounced

Check ALL your vacuum connections and also the clamps that fasten the two plenums together.

redcoupe86 · 04-02-2006, 08:33 PM

I've gone over every vacuum connection i can think of. The only ones im not really sure of would be the intake runners spacer and gaskets. I've sprayed carb cleaner at the base (when hot, not when the engine just started) and i didn't get any change in engine rpm. Now I guess i need to do it with the engine cold to be sure. Is there a better way to test the runners for vacuum leak?

If it turns out to be the intake runners, can they be removed fromt the engine with engine still in the car?

kqw · 04-03-2006, 08:07 AM

Quote:

Originally posted by redcoupe86
.....If it turns out to be the intake runners, can they be removed fromt the engine with engine still in the car?

You shouldn't have to remove them, just re-torque them down. 18ft/lbs.....

redcoupe86 · 04-03-2006, 10:23 AM

I suppose I could try that, however, if the gasket is missing or deteriorated, then I would have to remove and replace. Im assuming this can be done with the engine in the car.

kqw · 04-03-2006, 12:18 PM

Quote:

Originally posted by redcoupe86
I suppose I could try that, however, if the gasket is missing or deteriorated, then I would have to remove and replace. Im assuming this can be done with the engine in the car.

Yes......