Strange issues

X

x_atlas0

Well-Known Member
Messages
1,845
Reaction score
178
Location
Clarkston, MI
Hello, everybody.

Got my coupe back from the body shop on saturday. I'll post pics and make a new thread about it next weekend. On the way back from the shop, I noticed several new problems, and I'm not sure what could be causing them:

1. When cranking the car, it will turn on just fine, run great, idle perfectly, then when you take your hand off the key and it clicks fully into the run position, it dies instantly, like a fuel cutoff. However, if I run it up a bit while still holding the key (so it is against the threshold of start) then let the key go into run, it will bog for a second then pick up normally. So, something is happening when the key is going from start to run. Ideas?

2. The car gained a stumble of sorts between 2-3k. With constant throttle, I could feel the engine bucking periodically. The RPMs wouldn't vary during this, but I could feel the car surging and falling back. It was only at more than ~30% throttle.

3. No interior window power. I checked all the wires going to the loom, and none of them have any power. The gauges work, the lights work, but the rest has no power at all. Fuses are good.

Matters of note:
Engine is 1987 735, uses Motronic 1.3 from a 1991 735.
 
Sounds like there are wiring issues. I'd be looking for disconnected grounds, or possible a place where they pinched, cut or otherwise molested the main harness.

What were the panel beaters up to -- i.e., why was it in the body shop?
 
Yeah, pops thinks it is some kind of grounding issue as well, especially since the things listed either were not present before or they used to work. He wants me to completely reqire the car and make a complete new harness, but I just don't think I have the time.

The car was in the body shop getting an 80% resto, meaning the only things in the car were the drivetrain and the dash. The interior and the trunk were completely resprayed, as well as all rust fixed. There is still potential rust on the firewall and under the dash, but everywhere else is completely fixed. The paint was also redone in the same color (Fijord) with many coats.
 
1. Classic symptoms of worn-out electrical part of the ignition switch. There are a couple of contacts which partially burn up over time. I've had one where you could wiggle the switch after the engine started and make contact, but not a long-term solution.

The switch is held in the steering column by a small set screw. When you loosen the set screw, the electrical switch pulls back from the key part of the switch.

2. Probably not the answer, but check your distributor cap and rotor.

3. Check the wiring for power coming out of the fuse box?
 
1. Classic symptoms of worn-out electrical part of the ignition switch. There are a couple of contacts which partially burn up over time. I've had one where you could wiggle the switch after the engine started and make contact, but not a long-term solution.

The switch is held in the steering column by a small set screw. When you loosen the set screw, the electrical switch pulls back from the key part of the switch.

2. Probably not the answer, but check your distributor cap and rotor.

3. Check the wiring for power coming out of the fuse box?
Click to expand...

1. Thanks, I'll look into it next weekend, if I have time.
2. When I switched to Motronic, I changed to a new rotor and cap. Old wires, though.
3. I will also check on that. I was in a huge hurry to get the rear windows in and didn't have time to do a full check.
 
Based on the Bently manual, a drop in fuel pressure would cause a stumble. There is a bad fuel return grommet, compromising the fuel tank pressure integrity. Do you guys think that could be part of the problem? I plan to fix it as soon as possible. Right now it has a duct tape special.
 
The tank is not pressurised so no worries there.
However the fuel pickup in the tank can get bunged up with dirt and other crud, as 30csl found out, leading to fuelling and running issues. Might be worth a peek in the tank.
Malc
 
Tell me more about the Motronic conversion

Didi it have this flat spot prior to the body work?

If not, then I strongly suspect grounds. Check the engine ground, and make certain the Motronic harness is properly grounded AT THE ENGINE. If this ground circuit is not right, it will change the effective behavior of the AFM (that waffle topped thing with the flapper attached tot he throttle body), and this has a direct impact on the air fuel mixture at different RPMs and loads. If it runs well except at that specific spot, then it is almost certainly an issue in the Motronic circuits, and grounds are the first place to look.

S
 
Following up on what Malc said, check the fuel filter, too. If it gets gummed up, mid-range stumbling is a problem.
 
I moved the car to the new house this weekend, but it was unfortunately not without incident.

On the way over, I was driving along, everything was peachy. Car wasn't warmed up, so cooling was still in the blue. The stumble seemed to be gone, and the car really picked up at about 3k RPM. About half way to the new house (~1 mile to go) the coolant suddenly shoots into the red. Since I was so close, I cut the engine and kept going. (mostly downhill the rest of the way) When I got to the new place, with my now sore arms (man, I never knew power steering was so nice) I opened the hood and saw rust-colored coolant all over the place. It looks like it had boiled over the overflow tank and shot out the overflow outlet near the cap. After a few hours, I fired up the engine to move it into the garage without incident, engine fired up easily, idled fine, so I don't think I blew the head gasket, nor did I see any oil in the coolant after I had refilled it.

This whole episode was very odd, since about a week earlier I had drivent it back from Cartersville, GA to my home with no cooling problems at all.. (~50 miles) I saw no coolant leak when I pulled it out of my old house. I don't know what happened. My first thought is that the thermostat is stuck, but it is a new thermostat, and it worked a week before. The only other thing I can think of is the cooling system got an air bubble in it. How, I am not so sure. The only time I could have changed the composition of the cooling system is when I put the heater from cool to hot.

Any ideas?
 
Overheating

Sounds like combustion gasses in the cooling system. Bad headgasket would be better news than a crack in head. But I would bet on the latter. Hope it's neither for your sake, but doesn't sound promising. A leak down test might be in order. Check plugs to see if one stands out in color. It might narrow your focus. Good Luck!
 
Re: Overheating

Sounds like combustion gasses in the cooling system. Bad headgasket would be better news than a crack in head. But I would bet on the latter. Hope it's neither for your sake, but doesn't sound promising. A leak down test might be in order. Check plugs to see if one stands out in color. It might narrow your focus. Good Luck!
Click to expand...

I don't think there is a head crack or HG failure, as the exhaust is normal, no smoke of any kind. There is a pinhole leak in the radiator, on one of the endtanks.
 
It sounds like you had air trapped in the system which would cause the symptoms you describe.
Brown water suggests the system is rusty and possibly silting up. Suggest you flush the system and always use at least a 40% antifreeze mixture even if you live somewhere warm as it stops corrosion

Is the hesitation still there? Did you change fuel pumps when you changed engines? The Motronic system pump is a different flow rate and in the tank is a "priming" pump (was on my E28).

The other things about Motronic systems is that they are very sensitive to airleaks down stream of the air flow meter, and dirty electrical connections
Malc
 
I think it is the air because something very similar happened before, and it worked fine after I bled the cooling system. As to how the air got in there in the first place, I have no idea. It could be the pinhole leak, combined with sitting, may have allowed sufficient air to be displaced into the system to make a bubble, probably right by the thermostat housing. A radiator flush is very high on my list of tasks to do, I have had it with trying to monkey around with the cooling. The rad is the only stock thing left, aside from the overflow tank. I'll probably end up having a custom aluminum one made or try to retrofit an E12 rad or something. Given how E39's like to blow the plastic endtanks (especialy right around the upper radiator hose neck area) I'll try to stay with metal endtanks.

As for the hesitation, I didn't notice it, although it was a very short drive and I didn't get much of a chance to "goose" the car. The one time I did, I felt no hesitation. Given how low on gas the car was when I picked it up and the length of time that gas had been in the car, it is possible it was the filter clearing out all the sediment. Regardless, I didn't feel it this time. The car has a Motronic fuel pump outside of the fuel tank.

The car doesn't seem to have any intake leaks, as that would make the car idle poorly. The only place with an intake leak is before the AFM, and that is because of my rush job to put an air filter on the car. I recently got the Miller M30 MAF kit, and was planning on putting a proper air intake on the car then. Of course, before any such performance mods are made, the car will work well first.

Thanks for all the ideas, everybody.
 
You must log in or register to reply here.
Back
Top