Hi all, new user to Cadillacforums.com, and figured you all could give me a hand with a problem. I have a 1985 Seville with the 4.1 HT4100 engine that I am working on. It was brought to me because it had a severe lack of power, but after I did a tuneup it still does it. Now when idling or driving it will intermittantly stall out, to the point of dying (feels like you are running out of fuel). Today is extremely hot compared to the last times I have been driving it, and it seems to get worse after it sets. The hotter it is the worse it is. Gas tank is 1/2-3/4 full. Here are the things I have done so far:

Cap/Rotor, Plugs, Wires, PCV, Fuel Filter, cleaned TB, adjusted IAC and TPS, air filter.

The only code I am throwing is a code 53. I assume thats the Control module in the distributor? I guess that heat would affect its running as well. I can also say that when it does this intermitant running, stalling that I can see the TBIs intermitantly spraying as well. (Fuel PSI is constant at 9-10PSI) Would the module in the distributor control those? Thanks for any help you guys can give!!

That package has idle speed control (ISC) not an IAC...right..??


Checked the fuel pressure..?? Seems the most obvious thing for lack of power like you describe. There is a schraeder valve fitting on the fuel inlet pipe to conveniently check it. It should remain 10 PSI constant under load. Check the pressure while driving when the loss of power occurs.

The code 53 means that there is an interrupt in the reference signal from the distributor to the ECM. Another real good guess for the loss of power and stalling as the system will not run without the distributor reference signal. Diagnosing the loss of the distributor reference signal could involve the HEI module inside the distributor , the pickup coil that surrounds the star wheel inside the distributor or some of the wiring between the distributor and the ECM. The pickup coil connects to the HEI module at one end of the module inside the distributor. Disconnect the wires from the HEI module and use a VOM to check for continuity on the pickup coil when you wiggle the leads to the pickup coil and heat the pickup coil with a hair dryer or other heat source.

Yes, you are right, its the ISC not IAC. The fuel pressure seems to be constant at 10-11psi under load. Thing is, now that it has cooled down outside, it won't do it anymore, which leads me to think Vaporlock, but I was always under the impression that that was impossible on FI cars. I did notice however that the TBI units were not spraying/spraying eraticly whenever it had the stalling out though. If it does it tommarow when its hot, I will look into the computer sensor data, and monitor what it says for injector pulse width. I even dumped 2 cans of that lucas injector cleaner in the tank.

I also cleaned the 4-pin connector from the distrubutor and reset the codes, and after 1/2 hour of driving the car didn't stall once, or come up with any codes. It did seem to have a hesitation especially at WOT!! I may take a VOM and check the coil resistance and the TBI injector resistances tommarow as well... Is it possible that the control module is weak, causing a weak spark?? Or that the module somehow triggers the TBI injectors??

I can also tell you this, if I barely press the gas (1/8-1/4 pedal) it seems like its gonna have some power to it, but the more I press the throttle, the less it responds.... if that makes sense. Like if I am at 1/2 throttle, and I punch it down, it doesn't act like it wants to pull, it just kicks down, and revs up and sounds like it wants to. Almost reminicent of a bad accelerator pump in a carb.

Check every vacuum hose.Replace all that you can.


Get some fuel injection system cleaner and put it in the tank when you're down to about 12 gallons in the tank. Once it's thoroughly mixed in try a few wide-open accelerations.

Replaced all the vacuum hoses, still no power. I also dumped 2 things of that Lucas fuel system cleaner in it, at under 1/2 tank and ran it till the gas light came on, no help either. Could it be plugged cat? Is there a way to test for that? I honestly believe it was heat related, b/c yesterday was a SCORCHER (90*+). I will have to see if it gets hot again today, and see if it does it again.

Uh....did you check the pickup coil as recommended. Adding fuel system solvents is not going to effect a code for the ignition system.!!!


Read previous posts (search archives using "fuel pump" ) about fuel system cleaners and additives destroying fuel pumps , especially when used in stronger doses than recommended. If your fuel pump WAS ok it may not be now after running two bottles of cleaner in 1/2 tank..... The solvents can eat the insulation off the windings in the fuel pump armature and destroy it.

Hey, I didn't know that about the Fuel Pump, glad I know now!!! I did connect an Ohmmeter to the pickup and got about 700 ohms even when wiggling and heating the coil. Autozone states that they can test the module, so I guess thats the next step.

UPDATE----

I really need to get rid of this car, I am at the end of my ropes with it. I think I have figured out the problem, but don't know how to solve it... When the car is first started up for the day it runs like a CHAMP. After its been driven a while, and gotten hot, if its parked for a while it won't restart for nothing. I did find something interesting. If I bleed the fuel pressure at the test point I get some fuel and a LOT of air. If I bleed it, then restart it it'll start RIGHT UP!!! This leads me to think that the fuel in the line is evapotating, almost like a vapor lock, problem is I thought that was impossible on a FI car. Fuel PSI stays at 10-12 at all times, so that makes me think its not the pump. Anyone have any suggestions??

So does anyone think that a fuel pump will solve this, before I go just putting on more random parts??

Before you do, try repositioning/insulating the fuel lines.

Insulate with what? Could I cut the steel, and splice in a piece of rubber line to get it away from the engine?

Don't cut your fuel line. If there truly is air/vapor in your fuel line it is not from our old nemesis vapor lock. This occured because old fuel lines were under vacuum from the fuel pump at the engine. The Reid vapor pressure of the fuel is directly related to temperature & is controlled by the fuel refiner. It is always lower than atmospheric pressure except under very high heat conditions at low atmospheric pressure conditions (e.g. pulling a trailer up a long mountain grade). Our fuel systems should never be less than 9 p.s.i. above atmospheric pressure; therefore, should never experience classic vapor lock.

Air is getting into the fuel line in the tank before/as the fuel is pressurized or from a leak at the pressure regulator or one of the fuel injectors after the pump is shut off.

If I had a leak in the line, wouldn't I see the lines under the car being wet, sense the pump is in the tank, and there is pressure from the tank foreward?? I put on a different TBI already from a known good car and it was the same thing. It only is when the car is hot/been driven a while. And when she won't start all I gotta do is go pop the tab on the fuel pressure test port until gas comes out instead of air, and she'll fire right up.

If I had a leak in the line, wouldn't I see the lines under the car being wet, sense the pump is in the tank, and there is pressure from the tank foreward??

Yes, definitely.

Put it on ramps today, and looked all over for wet areas around the lines and find none at all :( . This car is like that car "Christina" from Stephen King's movie!!