88 mustang losing power when warm

[spierce]

302, GT40P heads, Edelbrock intake, 24lb injectors. MAF conversion
New TFI module, new coil, Tried with and without MSD box. with and without kenny bell BAP, AEM wide band. No smog system.

I pulled the codes and the only codes are related to the Smog stuff and tad/tab, and I get the VVS code since I don't have a harness connected to the unit.

So what the car does:
The car has not had any parts added to the car since I started having these problems... it was running fine, and now it's acting up. I road race the car and the problems started while I was at the track.

The car drives fine for about 10 minutes (car heats up in about 3-4 to a temp of about 190F), then there is a noticeable drop in power and the car starts going lean.. and I'm talking off the wide band lean 16+ and the car backfires (sounds like on the intake side).
It only does this above 2200 RPM's. so under a light load the car acts like the power is there but once I hit that 2200 RPM range the power drops off and the car is going lean.

I have new spark plugs, wires, cap, rotor, TFI module, and a coil.
I've run with and without the MSD box (and set my plug gap to down in the .048" and .054" without the MSD).
I've pulled the IAC plug while running (and hot) and the car still runs and doesn't really drop in RPM.
I've tried 2 TFI modules just to make sure my replcement wasn't bad.
I've pulled the distributor about 10 times to make sure it's installed in the correct position and timed right. I set the base timing to 10 deg with the plug out.

 

[spierce]

leakdown test

I did a quick leakdown test on the 5-8 cyl. bank and they all held pressure. I forgot to take the radiator cap off to check for a blown gasket though so I may have to repeat this tonight.

 

[ID89GT]

Hook a fuel pressure gauge up and see what your fuel pressure is at when you hit the 2200 rpm mark. If it drops very quickly then you probably need a fuel pump. Sounds like it to me anyway.

 

[spierce]

Fuel pump

Sorry probably should have listed that too, I've got a fuel pressure gauge too and it stays right at about 36 psi the entire time, no drops.

 

[stykthyn]

Injectors going out?

 

[ID89GT]

Or maybe the maf isn't calibrated to the injectors?

 

[spierce]

MAF

The Maf is a C&L and I've got the tube their site says, and the car was driving fine for a year with these injectors and MAF.
Though I am close to getting another maf just to try it out.

 

[spierce]

Injectors

Is there any way to check injectors if they are going bad?
I would think if they are going bad then this wouldn't be such a repeatable problem.
The fact that I can go out at any part of the day and drive the car HARD or like an old lady and 10 minutes in I loose power and it feels like it's taking all the timing out.

One thing I may try tonight is to get the car warmed up and after it starts acting up put the timing light on it and rev the motor and see where the timing is going to.

 

[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

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.

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.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

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.

 

[spierce]

I finally got out to take a look at it and do a little diagnostic work on it, and judging by the bubbles in the radiator and the amount of water thats missing I think it's got a blown head gasket. I'll be pulling the head this weekend.