No start warm (More)

T.Hanson · Post by **T.Hanson** » Sun Aug 28, 2011 3:02 pm

If the doctor says shut up and buy a new coolant temp sensor, o.k.

635 Euro has only one sensor on the thermostat housing. Weird from all the realoem drawings, but the car has run fine.

Question: If the sensor is unplugged, what happens ? I.e., I'm under the impression a bad sensor allows flooding when warm. Unplugged does it send warm, cold or none of the above ?

I've tried testing the sensor. Set meter to Ohms. Both wires connected, or disconnected, or the sensor removed, touching the probes to the male connectors on the sensor, I get nothing. Zeros. Yes, I have no idea what I'm doing, having read somebodies previous testing post.

Checked timing @ 2200 rpm. Switched out fuel pressure regulator w/spare. Car starts as normal cold, revs, idles fine. Some missing at idle but the car hasn't been driven on a freeway for quite awhile.

Obviously I have a phobia for installing $55 parts to find out that wasn't it.

Mike W. · Post by **Mike W.** » Sun Aug 28, 2011 8:47 pm

Just one sensor? Does the temp gauge work? If so it's running that, not the FI. You didn't say what year, but some, the ones with the old style water aux air valve used a switch down by the aux air valve. I'm not sure what it did, but someone may have plugged something else in there. Maybe in the radiator? I had a loose connector on an E24 of all things one time and anything over half throttle it would cut out. Suggesting it wouldn't run without it. What does your one sensor look like?

T.Hanson · Post by **T.Hanson** » Mon Aug 29, 2011 8:20 am

Thanks Mike. I sent you photos.

635 Euro is a hybrid, body shop '78 630/633 carcass w/635 transplant and all the Alpina toys. New 4 speed, clutch, etc.

I believe the ecu says 633 on it with marker on masking tape. Old style throttle body with single position switch box. Most everything else looks identical to '79 528i. The engine runs, has run very well until problems with starting warm.

Radiator looks the same as 528i except the sensor on the bottom hose corner is larger and has four male connectors. One of which is broken, but I think it runs the aux fan. So far not taken out to run enough to be an issue.

I will test anything as directed.

T.Hanson · Post by **T.Hanson** » Mon Aug 29, 2011 9:00 am

If it matters, the fuel gauge is stable, temp gauge appears to work normally. Both fuel pumps, lines, filter are new specs. The spendy aluminum spark booster box inside the fender by the coil is new.

Engine was stripped to the short block, cleaned, assembled, valves adjusted, plugs, plug wires new, grounds cleaned, blah, blah and it has run very well.

Switched out the fuel pressure regulator, to start run fine,...until warm. Neither unit leaked w/vacuum line pulled.

Start, run, rev, idle, until warm. Turn off. Turn the key to restart it spins over, no start. It may catch, bumble fumble, chug to let go of the key, then spin off. Smoke from the area around the throttle body. If it has started on an odd occasion ( not warm enough yet) it acts flooded, needs clearing out.

T.Hanson · Post by **T.Hanson** » Mon Aug 29, 2011 2:33 pm

The bellows between the AFM and throttle body was loose, AFM side. Installed new L rubber air tube between airbox and AFM, bellows is new. Tightened all clamps.

Unplugged coolant temp sensor, gauge in dash went from warm to zero.

Checked distributor. With rotor on the notch at TDC it will swivel both ways about equally to retard or advance.

Start. Time without light, vacuum tubes connected. Retard too far it stumbles, idles rough to kill. Advance while working linkage, revving, stop where it takes throttle as if stomping the pedal. Runs fine, idles @1200 rpm.

Question: Advance to no stumble ever, cold or warm ?

Shut off warm. Spins on start unless pumping the gas pedal or holding it open. Upon start it wants to be revved for clean out.

At least now it starts w/pedal input.

grumpsjr · Post by **grumpsjr** » Mon Aug 29, 2011 3:08 pm

I wonder if you have a leaking cold start injector, which could be causing the flooded-like condition you allude to. Apologies if you've already covered that in a previous post.

On Mon, Aug 29, 2011 at 12:33 PM, T Hanson <trhanson@earthlink.net (trhanson@earthlink.net)> wrote:

The bellows between the AFM and throttle body was loose, AFM side. Installed new L rubber air tube between airbox and AFM, bellows is new. Tightened all clamps.

Unplugged coolant temp sensor, gauge in dash went from warm to zero.

Checked distributor. With rotor on the notch at TDC it will swivel both ways about equally to retard or advance.

Start. Time without light, vacuum tubes connected. Retard too far it stumbles, idles rough to kill. Advance while working linkage, revving, stop where it takes throttle as if stomping the pedal. Runs fine, idles @1200 rpm.

Question: Advance to no stumble ever, cold or warm ?

Shut off warm. Spins on start unless pumping the gas pedal or holding it open. Upon start it wants to be revved for clean out.

At least now it starts w/pedal input.

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T.Hanson · Post by **T.Hanson** » Mon Aug 29, 2011 6:50 pm

Will test, swap if necessary. Thanks.

Mike W. · Post by **Mike W.** » Mon Aug 29, 2011 8:35 pm

It could be the temp sensor that's mounted down below, but don't discount the AFM. Which one is it and is it for that ECU. Plus there is a temp sensor in the AFM for air temp. Just for s*** and giggles, get a can of carb cleaner, the spray stuff and keep it handy. The next time it won't start, try priming things with it and see if it will. Flooded and starving can feel awfully similiar sometimes. If it doesn't start, pull a plug or two and see if it is flooded, the plug will be wet if it is of course.