Coughing Hearse

ANY help will be appreciated....

1990 Caprice Hearse 307ci ~52G miles. Engine "surges" (service manual calls it "chuggles") at about 40mph and/or under moderate to heavy acceleration.

So here are the details:

Overheated a while ago. I assumed a hose burst. Turned out to be a leak in the intake manifold gasket (by cylinder #7).

Here are the parts replaced:

Cap, rotor, wires & Coil (all Blue Streak)
EST module (AC Delco)
Plugs (Bosch)
All coolant hoses, thermostat, coolant, rad cap (15 psi) (Stant)
Radiator (cleaned, tested at local shop)
Water pump
Fuel pump
Vapour canister filter
Coolant temperature sensor
Oil pressure sensor
O2 Sensor (Bosch)
Intake manifold gasket (bolts torqued to spec) (Fel-Pro)
Carb base gasket (Fel-Pro)
EGR Valve & gasket (torqued to spec) (AC Delco)
Choke tube gasket (Fel-Pro)
PCV valve, valve cover grommet and hose to carb (FRAM)


The problem still exists. I have run out of ideas and what to test. BTW, the MAP sensor holds vacuum and the EGR is fine. Only codes I get from grounding the diagnostic connection are "13" and "14" (one long flash followed by short ones).

**ERROR CODES NO LONGER PRESENT*** :smile:

Checked for vacuum leaks. Vacuum gauge holds steady at idle. Engine runs smoothly. Gas mileage has improved (marginally) since all repairs. Check engine light NOT on. Double checked all vacuum lines to make sure they are connected, and in the proper place.

I know this is a lot to read, but, like I said, I have run out of ideas. :runaround:

Thank you for your time to read (and hopefully answer!)

Code 13 Oxygen sensor circuit (open circuit)

Code 14 Coolant temp sensor circuit (hi temp indicated)

I did check the codes....that is why the two sensors were replaced (and reconnected!)

This is why it is such a mystery!

BTW, Blt2lst...the Jet Chip in your 307....any big gains? Worth the investment? Other mods you made?

I did check the codes....that is why the two sensors were replaced (and reconnected!)
This is why it is such a mystery!
BTW, Blt2lst...the Jet Chip in your 307....any big gains? Worth the investment? Other mods you made?

Check out the attachments for diagnostic procedure for your problems. I copied them from the factory service manual.
Code 13 refers to an open circuit, not necessarily a bad sensor.
Code 14 could be a overheating problem, What condition is your radiator in? If it is old and clogged, you will have overheating problems.

As far as the jet chip goes, My 307 is mostly stock and the chip is the first thing I tried to improve performance. It was only supposed to improve WOT performance, not really sure it made much of a difference at the time. However, what did make a noticeable difference was to have a performance rebuild done on the Q-jet carb. The chip probably makes more of a difference now that the carb has been rebuilt but I would have to install the old chip to see if there really is a difference, and that's not going to happen anytime soon.. Unfortunately, the late model olds 307 engines have limited performance potential due to the head design.

So to sum up:
any big gains? No
Worth the investment? Maybe


Good luck


file:///C:/DOCUME%7E1/alan/LOCALS%7E1/Temp/moz-screenshot.png

Code 13 refers to an open circuit, not necessarily a bad sensor.
Code 14 could be a overheating problem, What condition is your radiator in? If it is old and clogged, you will have overheating problems.

I have the same service manual...I should have mentioned that....the O2 sensor was 20G miles old which is the only reason why I replaced it, and the radiator is in good condition. I did take it to a shop and had it properly cleaned and tested. They said it is running at 80-90% efficiency, up from about 30-40% when the car overheated.

I don't have a digital ohmmeter....unsure how else to check it.

Further, the "scan" tool won't communicate with the car....but that is another problem...(new Innova 3120)

I don't have a digital ohmmeter....unsure how else to check it.


You will need a digital voltmeter to do any further testing, no way around that..:shakehead

with your issues when did the engine overheat exactly ?

after this overheating what was the compression ?

you replaced this O2 sensor after this internal coolant leak ?

what is the vacuum at idle ? @ RPM ?


some Items to replace with the age of this engine : EGR , radiator if its full of scale and or the cooling external fins are corroded , fan clutch.

the 3 core radiator is required when towing or in a operation of hauling with these vehicles replace radiator cap 15psi.

coolant replacement every 2 years is required. distilled water is what I use with engine coolants ...

having owned this engine for 17yrs 380,ooomi I found that if properly maintained these engines are very durable.

[quote=Filmfest Guy;6816118]Code 13 refers to an open circuit, not necessarily a bad sensor.


Rechecked the circuit (visually) for the O2 sensor. Appears fine.
Checked the error codes again (by grounding the test terminals) and I now have no error codes (just Code 12, which is fine)

Code 14 could be a overheating problem, What condition is your radiator in? If it is old and clogged, you will have overheating problems.

The rad is fine. Cleaned, has no leaks or cold spots. Thermostat, etc all new. Fan clutch appears fine...Overheating has not been a problem since the gasket leak.

Back to the reason for this post, could the 40mph "chuggle" be a coil or EST problem?

with your issues when did the engine overheat exactly ?

after this overheating what was the compression ?

you replaced this O2 sensor after this internal coolant leak ?

what is the vacuum at idle ? @ RPM ?


some Items to replace with the age of this engine : EGR , radiator if its full of scale and or the cooling external fins are corroded , fan clutch.

the 3 core radiator is required when towing or in a operation of hauling with these vehicles replace radiator cap 15psi.

coolant replacement every 2 years is required. distilled water is what I use with engine coolants ...

having owned this engine for 17yrs 380,ooomi I found that if properly maintained these engines are very durable.


Overheated on July 30. Compression not checked. No oil in coolant, and no coolant in oil, so I didn't bother. Vacuum test is 19psi at idle.

EGR valve manually tested. Engine runs rough when diaphragm moved, and unit holds vacuum.

Amended my original post, that I had the rad serviced and tested and it is fine. New coolant, thermostat, hoses, and cap after overheating, and have had no cooling issues since. Even in August after I fixed the A/C and used it constantly.

This, however, put the extra strain on the engine and caused the "chuggle" problem to happen upon any acceleration.

As in my above post, wondering if it is a coil or EST problem...although I have no error codes to suggest that.

Overheated on July 30. Compression not checked. No oil in coolant, and no coolant in oil, so I didn't bother. Vacuum test is 19psi at idle.

EGR valve manually tested. Engine runs rough when diaphragm moved, and unit holds vacuum.

Amended my original post, that I had the rad serviced and tested and it is fine. New coolant, thermostat, hoses, and cap after overheating, and have had no cooling issues since. Even in August after I fixed the A/C and used it constantly.

This, however, put the extra strain on the engine and caused the "chuggle" problem to happen upon any acceleration.

As in my above post, wondering if it is a coil or EST problem...although I have no error codes to suggest that.


disable the EGR to see if the valve is opening too much too soon. over time the spring in the valve gets weak . vacuum at 19 inches and steady should mean the compression is good.

check the fuel pressure/carb filter 7-9psi approx.

check the fuel pressure/carb filter 7-9psi approx.

Fuel pressure should be around 6 psi

Fuel pressure should be around 6 psi

Fuel pressure is a steady 6psi.

When I had the rad, hoses, etc off, it was easier to put a new fuel pump on whether I needed it or not. Also a new fuel filter.

I removed the EGR valve from the intake mani, and there was very little carbon buildup, but cleaned it nevertheless.

Also pulled carb off the intake manifold. Made no adjustments to carb since these ones can be temperamental.

New gaskets under both, and all bolts torqued to spec.

BTW, found a new EGR from RockAuto for about $30...will replace that....there just isn't that much more to try!

Vacuum test is 19psi at idle. .

Is it a steady 19" vacuum or does it fluctuate?

Fuel pressure is a steady 6psi.

When I had the rad, hoses, etc off, it was easier to put a new fuel pump on whether I needed it or not. Also a new fuel filter.

I removed the EGR valve from the intake mani, and there was very little carbon buildup, but cleaned it nevertheless.

Also pulled carb off the intake manifold. Made no adjustments to carb since these ones can be temperamental.

New gaskets under both, and all bolts torqued to spec.

BTW, found a new EGR from RockAuto for about $30...will replace that....there just isn't that much more to try!


what is the vacuum at 2000 rpm when the engine held at that rpm steady ...if it stays high at 19 inches it is good if it drops could be restriction in the exhaust...

The vacuum is rock steady at 19". No fluctuation. Holds the same at 2000rpm as well.

Did you correct the trouble codes yet?

Yup, trouble codes clear, no new ones and problem still exists.

The absolute last thing I want to do is start messing with the carb, but there really isn't anything else to check, replace, clean or repair.....

The absolute last thing I want to do is start messing with the carb, but there really isn't anything else to check, replace, clean or repair.....

If you don't know when the last time the carb was rebuilt, it is probably time..:banghead:

It made a world of difference when I had mine done.




.

Yup, trouble codes clear, no new ones and problem still exists.

The absolute last thing I want to do is start messing with the carb, but there really isn't anything else to check, replace, clean or repair.....

what about the EGR replacement ?

If you don't know when the last time the carb was rebuilt, it is probably time..:banghead:

It made a world of difference when I had mine done.




.


What doesn't make sense is that there would be a carb problem after the car overheated.

And the carb has never been done. When you rebuilt yours, did you buy a re-manufactured carb, or use a carb kit in the original?

what about the EGR replacement ?


The EGR has been replaced, and there was no difference in the "chuggle" problem.

I cannot express how frustrating this is now!:banghead:

Just a thought, have you checked the vacuum operated exhaust valve on the left side downstream from the exhaust manifold?
If it frozen in the wrong position, that may cause some sort of exhaust restriction and maybe some driveability problems. Not sure what happens when these fail, just my theory. To check, apply vacuum and observe valve, plunger should move freely and it should hold vacuum also,

What doesn't make sense is that there would be a carb problem after the car overheated.


Stranger things have happened..:screwy:

And the carb has never been done. When you rebuilt yours, did you buy a re-manufactured carb, or use a carb kit in the original?

I had these guys rebuild mine.. Worth the money IMO.

http://smicarburetor.com/products/sfID1/85/sfID2/86/sfID3/34/productID/432

The EGR has been replaced, and there was no difference in the "chuggle" problem.

I cannot express how frustrating this is now!:banghead:


remove the new EGR valve plug the exhaust port that is now in view. check to see that the port going to the intake manifold has vacuum.

Just a thought, have you checked the vacuum operated exhaust valve on the left side downstream from the exhaust manifold?
If it frozen in the wrong position, that may cause some sort of exhaust restriction and maybe some driveability problems. Not sure what happens when these fail, just my theory. To check, apply vacuum and observe valve, plunger should move freely and it should hold vacuum also,

the valve is working, albeit slowly. It does open fully, and hold vacuum.

(I had high hopes for this one!)

Took the car through its annual mandatory emissions test today, and passed with flying colours. Although HC has increased marginally from .61ppm to .74ppm, NOX and CO both dropped.

Does this give anyone any more ideas?

I had these guys rebuild mine.. Worth the money IMO.

http://smicarburetor.com/products/sfID1/85/sfID2/86/sfID3/34/productID/432

Checked the site, unable to find an application to match my carb.

This would be one of the last options, simply due to the cost....

Checked the site, unable to find an application to match my carb.

This would be one of the last options, simply due to the cost....

You should have the electronic q-jet carb, they do have them or they can rebuild yours.
Rebuilding yours is the least expensive way to go.