I have been running a thread in the 2nd gen board but I'm running out of ideas so I thought I would try here...

- 87 GXL

-just rebuilt the engine. Most internal pieces replaced... apex seals/springs, oc rings and rubbers, etc. etc.

-injectors cleaned and tested by Cruisin Perfomance.. they came back A+

-new fuel filter and thermostat

-the car will start right up and idle beautifully at 800 rpm's. Fast idle works just fine. BAC tested ok.

-does seem to run rich as the plugs are black. But I've run the car at idle for about 10 hours now so I can see that happening. Just replaced plugs with new ones and didn't make a difference with my problem

-the problem:
if I go from idle to wot all at once the engine just bogs down and will not deliver power with lots of rpm bounce. I get a weird sound from the AFM almost like the flap can't make up its mind to open or close. It flutters in other words. But it is not stuck it moves freely and springs back to closed position, I checked. The other problem is I can build power gradually to about 2,700 rpm's with no problem then I get the same condition as I previously described. I drove the car up my street and it seems to have a huge lack of power. As I previously mentioned, I have good compression and great idle but seem to lack good combustion/power for some reason.

What I've done:
-rechecked timing about three time including pulling the CAS and realigning it

-rechecked all conections both electrical and vacuum. It's all there and plugged in.

-swapped the AFM and CPU with others. No change

-checked all throttle connections and also checked the plates. They are free and are opening as they should.

-ran engine diag with my homemade tester (I love that thing) and received only one code which was O2 sensor but even that is intermittent.

- tested ACV. got some weird stuff here. Air blew out the valve into the air silencer tube at idle which FSM indicates it should only do at 1500 rpm's plus. No air out the relief solenoid tube. So, this may be a problem ACV. Anyone think that would cause the symptoms I am getting?

-Can't remember specifically but if I put the exhaust gasket on wrong and covered the little hole from the engine would this cause AFM problems. I just don't want to tear off the exhaust if I don't have to. I don't think I did this but who know's???

My other thoughts are that maybe somehow I am getting negative pressure back through the throttle body and back to the AFM. Not sure if that is possible but it's the only thing I can think of to make the AFM react the way it does.

Any thoughts or idea are greatly appreciated... I'm at a loss. Thanks in advance for any posts!

 

Have you checked the fuel pump? it sounds like it's not getting enough fuel and attempting to compensate, but only managing to keep it going at low revs.

Check the fuel supply lines aren't kinked or getting squashed somewhere as well just to be sure.

 

Thanks chairchild. I think I will check for fuel pressure tomorrow.

 

Apply power to each of the injector to make sure they click. Sometimes the injector cleaner stuff seems to make the injectors stick if they sit for a while after the cleaning.

-Max

 

Worth a try Max. Thanks

 

Update....
I keep gong back to the the problem and the different conditions in which it happens. Idle to WOT lack of power and noise happens immediately. Gradual build to 2700 rpm's then it occurs. I look at the different scenarios posing the same ultimate problem. I'm starting to believe it is a fuel delivery problem. If the throttle opens up right away (idle to WOT) it gets no power right away which brings me to fuel. If I gradually build power it ultimately does the same thing at 2700 which again could be fuel delivery but because I built the rpm's gradually the fuel pressure can adjust slowly but not rapidly. What ya think??? But, I guess the opposite could be true... plenty of fuel but not enough intake air at either condition.

Also, I checked compression with a gauge. I was pretty surprised.... 101 on the back, 97 on the front. All even bounces. Figured that was pretty good for a rebuild with less than 6 hours of run time. Sooo, it's not an internal problem.

 

It could mean many things. When you start up the car do you smell a lot of gas from the fuel (cylinder on the right side of the engine)?... forgot the damn word. That could be why your car is running to rich. Also there might be a vacuum problem. Try spraying some water to see if there is a leak somewhere. That might be the problem if its not getting enough air. It might also be an ignition miss. the lack of power might be the coils... they might be getting to hot. Like i said it could be many things. Even the small things accumulate problems.

 

Did you vary engine speed while running it in?

 

As I said it's only been running for a few hours but yes I have been varying the rpm's... trying to diagnose the problem.

 

Your injectors aren't "surging" like they should; when you floor it, they dump a lot of fuel in for a shot time to compensate for the sudden rush of air. If you've got a bad fuel filter, weak fuel pump, malfunctioning Fuel Pressure Regulator, bad boost sensor, bad atmospheric pressure sensor (not boost sensor), bad O2 sensor, bad water-temp (on the pump housing) sensor, sticky Throttle Position Sensor, or a myriad of other little problems like air leaks and bad gaskets, they could all cause this problem.

If you've tested everything under the hood and it's all in properly functioning order, then check the cold solder-joints on the ECU (passenger-side); verify the wiring harness is working properly (continuity check). You've got an 87; you may or may not have high-impedence injectors; if you have a resistor pack under the air-box, make sure that works properly, and make sure your injectors are the correct ones (ohm test).

Also, do a compression test on your engine; if it idles, then it should be okay, but it never hurts to check.

This problem sounds really similar to a bad accelerator-pump on a carburetor; but on EFI, everything fuel-system related (electrical or mechanical) depends on one-another to do that correctly. Check everything. I'll bet that your AFM is bad...