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740 Odd Hard Start Problem

colgate41

colgate41

Active member
Joined
Jul 31, 2008
Location
New York
Car in question is a 1991 740 Turbo sedan with 182K

This problem just started happening. The car is not a daily driver but does get driven from time to time.

When the car has sat overnight or all day it's very hard to start. It cranks and wants to turn over but wont unless I have my foot on the gas. Then when it does start, it sounds like something is squealing or rattling as the idle is erratic (all with my foot on the gas or it will stall) until after maybe 10-20 seconds it figurers it all out and settles down, I take my foot off the gas and it idles fine and then runs and drives no problem.

It will start right up after I drive it a bit without having those initial start problems.

I think this battery is a bit tired but I'm not sure if that would cause this behavior.

I've done some research and cant find any potential answers. Car has fresh gas in it and has new plug and a new ignition control module (which was the cause of no start at all a few weeks ago)

Thanks for any help!
 
So i gave it another shot today. I hooked the car up to my other car to jump it. I know the battery is old and from past experiences a tired battery tends to cause all sorts of odd problems and I wanted to eliminate that.

Same problem. Car "cranks" well and wants to start but unless I give it gas, it will not start. I give it gas and have to hold it at about 2000 or more rpm and it makes that "chugging" sound like it's not getting enough gas. Then after about 45 seconds to a minute it magically clears up and the car idles and drives fine. When I shut the car off and restart, it's fine, no problems at all. This seems to only happen from a cold start or sitting.

I disconnected the coolant temp sensor and had the same problem so I don't think it's that.

I feel like the fuel pressure is fine because the car runs really well after it gets past this starting issue.

Recent work done was a new exhaust from the headers back. So new cat, resonator and muffler. When I did the work I used some of that walker sealant around the connections (ended up not working really well). Any chance some of that goop got into the exhaust and could be causing some problems?

I also replaced the ignition module because it was causing a no start. All this was done at the same time. I drove the car to a car show and had no real problems with starting. This kinda happened all of a sudden.

Any chance the fuel filter is clogged or kinda clogged? And me holding on the gas kinda helps before the blockage is cleared? Once the car gets over its chugging and stuttering it runs fine and idles well with no problem.

Fuel filter is maybe 5-7 years old and the car was sitting most of that time.

Fuel pump is about the same age but primes up when the turn of the key no problem and doesn't make any odd noises outside of what its supposed to.

Hmmm
 
colgate41 said:
So i gave it another shot today. I hooked the car up to my other car to jump it. I know the battery is old and from past experiences a tired battery tends to cause all sorts of odd problems and I wanted to eliminate that.

Same problem. Car "cranks" well and wants to start but unless I give it gas, it will not start. I give it gas and have to hold it at about 2000 or more rpm and it makes that "chugging" sound like it's not getting enough gas. Then after about 45 seconds to a minute it magically clears up and the car idles and drives fine. When I shut the car off and restart, it's fine, no problems at all. This seems to only happen from a cold start or sitting.

I disconnected the coolant temp sensor and had the same problem so I don't think it's that.

I feel like the fuel pressure is fine because the car runs really well after it gets past this starting issue.

Recent work done was a new exhaust from the headers back. So new cat, resonator and muffler. When I did the work I used some of that walker sealant around the connections (ended up not working really well). Any chance some of that goop got into the exhaust and could be causing some problems?

I also replaced the ignition module because it was causing a no start. All this was done at the same time. I drove the car to a car show and had no real problems with starting. This kinda happened all of a sudden.

Any chance the fuel filter is clogged or kinda clogged? And me holding on the gas kinda helps before the blockage is cleared? Once the car gets over its chugging and stuttering it runs fine and idles well with no problem.

Fuel filter is maybe 5-7 years old and the car was sitting most of that time.

Fuel pump is about the same age but primes up when the turn of the key no problem and doesn't make any odd noises outside of what its supposed to.

Hmmm
Click to expand...

How old is the gas in the tank?
 
Disconnecting the ECT would give the same problem...a very hard cold start, and should be fine when hot. Id put my money on either a failed ECT or the ECT harness is shot. Just to be sure you are looking at the right one, its the farthest sensor towards the firewall on the head. Under intake runner 3.

I had the same issue when I bought my car, would take 10+ attempts to start, and usually would not unless I held the gas to keep it from dying. The aftermarket harness was the problem, spliced in a junkyard oem and all was good.
 
Kinda sounds like the FPR diaphragm is slowly leaking fuel into the intake which results in a flooded cylinder or 2 and low fuel pressure on startup. Pull the vacuum hose on the FPR and check for fuel in the hose.
 
Mbeas96 said:
Disconnecting the ECT would give the same problem...a very hard cold start, and should be fine when hot. Id put my money on either a failed ECT or the ECT harness is shot. Just to be sure you are looking at the right one, its the farthest sensor towards the firewall on the head. Under intake runner 3.

I had the same issue when I bought my car, would take 10+ attempts to start, and usually would not unless I held the gas to keep it from dying. The aftermarket harness was the problem, spliced in a junkyard oem and all was good.
Click to expand...

Thanks for the insight! I?ll check this out.
 
hiperfauto said:
Kinda sounds like the FPR diaphragm is slowly leaking fuel into the intake which results in a flooded cylinder or 2 and low fuel pressure on startup. Pull the vacuum hose on the FPR and check for fuel in the hose.
Click to expand...

I?ll also check this. Thanks!
 
colgate41 said:
I?ll also check this. Thanks!
Click to expand...

colgate41 said:
I?ll also check this. Thanks!
Click to expand...

Pulled the vacuum hose off the front of the FPR and saw no gas. I smelled a hint of gas but saw nothing. I left the vacuum off and the car started right up. I shut it down and then re-attached the hose and the car still started right up with none of the symptoms I mentioned earlier. Weird. The car was cold too, since the last time I tried to start it was sometime around 10am EST.

I'll try again in the am and see what happens.
 
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