Engine running rough at start-up

[heetseeker91]

Ok i'm new to this forum and i am needing some advice on what to do with my car. I have a '91 GT that i have had since 32,000 miles and a couple weeks ago i was driving and had the stereo blaring and wasn't paying attention to my temp gauge (the water pump went out) well, it got so hot the engine shut down. After the yelling and cussing subsided i got it back home and getting the water pump replaced it seems to run rough when it starts up also when i'm driving down the highway in 4th and 5th gear espeically when i'm going up hill it feels like its cutting out. Once the car is moving and has run for a few mintues most of the roughness is gone. I replaced the plugs, wires, cap, rotor, and fuel filter about 15,000 miles ago Checked timing and its dead on. I had the codes pulled and the only one that it showed was egr low voltage so i have a new egr on the way i'm just trying to cover all the bases. also is there anyway that i could check to see if any damage was done to the heads without pulling them? would a compression check tell me what i need to know? The engine itself is completely stock except for an off-road prochamber, flowmasters and cold air intake. I feel like a total idot for letting that thing get so hot it shut down but i'm just trying to figure out what the problems could be without taking it to a shop and just saying fix it and getting a bill a mile long and have to refinance my house to pay for it lol. Any help in this situation would be greatly appreciated, thanks.

 

[jrichker]

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should. See the Chilton’s Shop
manual for the complete test procedure

Dump the codes and see what the computer says is wrong…Codes may be present in the computer
even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check
engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing
test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no
functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same
bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same
bundle of wires as the self test connector.

Do not jumper anything to the single dark brown connector. It is the power for the
under the hood light. It is in another bundle of wires near the windshield wiper.

Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder
balance test. Low compression on one of these cylinders rules out the
injectors as being the most likely cause of the problem. Look at cylinders
that fail the cylinder balance test but have good compression. These
cylinders either have a bad injector, bad spark plug or spark plug wire.
Move the wire and then the spark plug to another cylinder and run the
cylinder balance test again. If it follows the moved wire or spark plug,
you have found the problem. If the same cylinder fails the test again,
the injector is bad. If different cylinders fail the cylinder balance test,
you have ignition problems or wiring problems in the 10 pin black &
white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark
plug hole. The other type leaks too much to get an accurate reading.
Your local auto parts store may have a compression tester to rent.
If you do mechanic work on your own car on a regular basis, it would
be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the
throttle wide open, crank the engine until it the gage reading stops
increasing. On a cold engine, it will be hard to tell what's good &
what's not. Some of the recent posts have numbers ranging from
140-170 psi. If the compression is low, squirt some oil in the cylinder
and do it again – if it comes up, the rings are worn. There should be
no more than 10% difference between cylinders. Use a blow down
leak test (puts compressed air inside cylinders) on cylinders that
have more than 10% difference.

See the link to my site for details on how to build your own blow
down type compression tester.