BelgiumLimowithaolds307

I have a Cadillac Limo with the 307 Y olds engine.
Engine runs perfect on Propane.
There is a problem when the engine is running on Fuel.
When the car is on park --> engine response is good from no gas to full gas (rpm)
When the car is driving in D --> engine response is good from no gas to full gas acceleration is good --> UNTIL the car hits the 31miles/h.
Then the engine is cutback (seems like there is no fuel enough) Under the 31 miles/h it drives good.
There is no problem when ther car is driving on PROPANE --> engine has a lot off power from 0 to 62 miles/h

actions done :
- tank cleanend
- new fuellines
- new fuelfilters
- engine test with a testtank+electric fuellpump directly to the carb --> same result --> engine is cutting back bij 31 miles/h

What can i do next to solve this problem

BillK

Has anything been done to the carburetor ? That's about all that is left. Probably time for a rebuild. When you test it in Park there is no load on the engine so a lot less fuel is needed.

BelgiumLimowithaolds307

The car was running well for about 30 miles.
The problems started after that.
There are no adjustments or rebuilds on the carburetor.

There are a lots of vacuum tubes on it.
Is there a test to run it with only the necessary tubes and blokking the other tubes ?

Sugar Bear

What year car?

Does the car have a check engine light? Does it work? Is it illuminated while driving? Can you check for trouble codes stored in the ECM?

I'm guessing at a stuck Mixture Control (MC) solenoid in the carburetor or stuck metering rods. Disconnect the MC solenoid on the top right front of the carburetor and test drive. Disconnecting should put it to full rich. With the car off but the key in the run position, can you hear the MC solenoid and the metering rods chattering in the carb?

There is a test lead not connected to anything for reading the MC duty cycle. The lead is between the carb and thermostat housing with a green plastic connector. With the car running using an old fashion point type dwell meter on the SIX cylinder scale connected to the lead what reading doe you get? It should be 30 degrees. If you cannot get a dwell meter use a duty cycle meter, the reading should be about 50.

If you rev the engine at idle do the secondaries on the carb open?

Does the choke blade open completely? It should be fully vertical when the engine is at operating temperature.

Good luck and keep us posted...

BelgiumLimowithaolds307

The cars built is 1988.
Check engine is illuminated all the time.
I can't get anny trouble codes out of it. It stays illuminated even when i shorted the A and B pin on the ADL connector.
Dwell meter gives 30°

I think that the checklampdriver is broken according to the fabrics manual.
Have to check that next week.
I will check the MC also

On gasoline its a lookalike broken Knocksensor --> tested it with the engine on idle and the remove knocksensor wire --> engine rpm is still the same
But i think that it is ok because the engine runs good on the propane. checked it today.


Thanks for the help

Sugar Bear

As I recall it is the top two pins on the right of the ALDL. The light should flash a code 12 with the car off but key in run position. 12 means no distributor reference signal because the car isn't running so 12 is good, other codes are not.

Lampdrivers don't fail often but it could be bad.

Either way I don't think that is the running problem. Did the light come on the same time as the problem started?

Check for the MC solenoid chatter when jumping the ALDL also.

Good luck!!!

BelgiumLimowithaolds307

With the car off but the key in the run position, --> the MC solenoid and the metering rods don't chattering in the carb
What signal has to be on the cable from the MC 12V ???

Olds64

You mentioned that the car is setup to run on propane. What modifications were done to do this?

BelgiumLimowithaolds307

Only mods are : the mixer and propane tank in the trunk.
Also there is a fuelrelais inserted between the fuelline.
--> This was tested end seems to be working very well
Mixer is like exaple in link
https://www.lpgwebshop.com/nl/home/4...cl-filter.html

I tested the MC and it did't make anny noise ???
How can i test the curent or tension on the connector ???

Olds64

For the car to run properly on propane the carburetor would have to be modified (i.e. new jets, metering rods, etc.). Since you measured 30* of dwell at the test lead that means your mixture control solenoid is working properly. I suggest you troubleshoot why you can't read codes on your ALDL. Check out this link to see how to pull codes by shorting the A and B terminals of your ALDL.

https://classicoldsmobile.com/forums...mputer-123831/

BelgiumLimowithaolds307

So after a lot of testing seems that the ECM memory tension + was broken.
Main power lead + high at all times was broken.
After fixing this problem --> ECM is back working

check codes where 12-12-12 .... 21-21-21
21 = TPS sensor
I have to check now the tension between lead B or C and GND , while B and C is bridged --> it should be 0.5V according the shopmanual
I suposed that the tension signal alternated between 0.5V-4.5V on lead A en C when trottle is moving from Idle to Open.

So this was it for today more testing later ;-)

steel-and-fire

Manage to fix the problem?

I have 89 Y VIN 307 and it sounds like the same problem I might have. It happened after an alternator failed and replaced. That is foot to the floor the entire time.

BelgiumLimowithaolds307

Altenator was chaged also, but that was not the problem.

My car reacts the same with the former carb.
You best can read the engine troublecodes for more info

First i repaired the computer Ecu's backupbattery voltage (lead was broken) after reading the ecu trouble codes seems that the TPS switch was broken.
--> we placed the backup carburator from a donor car that we possesed.
TPS trouble code was erased and TPS was working fine.
But .... Car won't drive wel on benzin --> new code appear --> O2 sensor this was ok but the MC valve is probely broken.
When i disconect the MC the car runs wel but verry rich with a big smell of benzine :-)
I am planning to rebuilt the former carb and have to look what kind of rebuilt kit i need for the Rochester 4 BB elektronic ecm controlled carburator
Has anyone did this before ? and wich tools i need for rebuilding?

Sugar Bear

I cannot draw a connection between the difference of running on propane vs. gasoline to this; but, try loosening the exhaust pipe at the exhaust manifold and test driving to rule out a restricted exhaust system. Catalytic converters used to plug/get restricted rather frequently and the car would lose power.

Good luck!!!

BelgiumLimowithaolds307

The exaust and catalyc convertor is open.
In Belgium we drive mostley on Propane because the benzin or gasoil is to expensive here.
1,54 Dollar/0.26 Gallon for benzine against 0,51Dollar/0,26 Gallon for propane

The car runs perfect on Propane because the propane is flowing with the propane adjuster so that the car only needs the throttle valve for acceleration.
With the car on Benzine(gasoil) need the car a fullworking carburator.

Sugar Bear

Do the metering rods chatter with the ALDL jumpered and the key in the run position?

With the engine warm and the air cleaner removed, running on gasoline, do the secondaries/rear flaps open on the carburetor when revving the engine?

30 degrees dwell on a six cylinder scale at MC is good.

Fuel smell with MC solenoid disconnected is good.

About rebuilding the carburetor, they are complex and require special measuring tools which are hard to find. If you take it apart get a manual, be methodical and measure and record any adjustments made. In my opinion, if it ran well before it is unlikely that something suddenly went out of adjustment and is more likely to just need a cleaning due to causing something to stick/bind.

Many repairs can be made to these carburetors with the carburetor left in place and only removing the top of the carburetor. A tip to reinstall the top is to use a flat putty knife to hold down spring loaded components, place the top on and then pull the putty knife out. Compare the old gaskets to the new ones, all of the holes must be exactly the same. When reinstalling, don't over tighten the screws and tighten them in the correct sequence.

Good luck!!!