FI diagnostics

[EightiesFan]

my 83 FI Spider will not make it up my inclined driveway. it idles and revs up fairly well. it accelerates over the flat portion of my driveway, but when it reaches the incline, the RPMs drop to idle speed regardless of accelerator pedal pressure. I suspect the AFM. I have checked for and found no air leaks. I have inspected the AFM flap and cannot find any problem with it or its operation. After checking for bad electrical connections, I intend to check the AFM on the ECU, (per Artigue's FI manual) but I am a bit confused about how to proceed. because of the lack of access to the back of the ECU, I am having a hard time figuring out how to unplug it. I dont want to damage anything with too much force. is there any trick to this procedure? What really confuses me, though, is how can testing on the ECU lend any information about the AFM if the ECU is not connected to the AFM when tested. I must not be understanding something about the proper way to perform this test. Also, what does failure of this test indicate about the AFM? thanks to anyone with helpful advice.

[rlux4]

The ECU has a boss on the end opposite the wire loom that hooks under a wire bar. There's a metal spring plate on the wire loom end. Pry the spring plate away from the plug body and pull the plug away from the ECU, wire loom end first, and the boss on the other end will disengage. The ECU's function is to respond to input from the sensors and "make" the ground connections for the injectors. It is highly unlikely to be bad, they are very simple and bullet proof. There are tests to perform as per Brad's diagnostics, and what they are testing is continuity in the unit. If you don't already have it, here's another good diagnostic manual to download:
http://www.angelfire.com/wa2/fits/index.html#ljetguide
I'm assuming your symptoms are consistent, and don't just happen on the driveway. Being as you're loosing power under load, I'd suspect low fuel pressure, due to a failed pressure regulator, or a fuel leak. You could check that with a pressure gauge, which you can easily put on the hose that supplies the cold start valve. Be careful when you disconnect the hose, the system is under pressure, so I wrap a rag around it as I disconnect mine.
Keep us posted on how it's going.
Ron

[So Cal Mark]

is the problem only apparent in your driveway or also out on the road? Will the engine rev normally? It's possible you have a catalytic converter that has failed and is plugged, not letting exhaust out

[EightiesFan]

Thanks for your advice Ron and Mark. This car hasn't been on the road for about 7 yrs. I have been spending the past few months trying to get it back into good mechanical condition. so far my test drives have not left the driveway. The cat converter is not very old, mileage-wise. the fuel pressure is 36-38 psi. this is true with and without the pressure regulator connected to the vacuum hose. I also tested the engine vacuum. it is only producing about 5" Hg vacuum. This is with the timing set at about 20 degrees BTDC. At 10 degrees BTDC is will not produce enough power to move the car over flat ground. At 0 degrees, it will not idle. should I attempt to advance the timing even further?

Zach Story

[So Cal Mark]

the low vacuum points to either incorrect cam timing or a plugged exhaust

[EightiesFan]

I removed the oxygen sensor and ran the engine, but this did not improve vacuum, so I don't think there is a problem with exhaust flow. The cam timing was about right, but I went ahead and advanced it about 10 degrees and this improved vacuum to over 10" Hg. There was a significant increase in engine power from this, and I am now able to drive around the neighborhood, but the engine is very week going up steep hills.
I then checked compression. dry test results were between 105 and 110 psi for all cylinders. wet test results were between 150 and 160 psi for all cylinders. I gather that I need new piston rings and that this is the main source of my lack of engine power. Is this the correct conclusion? Any advice for me before I attempt this procedure?

Thanks,
Zach

[So Cal Mark]

how did you advance cam timing 10d? Are you talking about ignition timing?

[EightiesFan]

at TDC, the cams were a little behind. at about 5 degrees past TDC the cam gears aligned with the timing pointers, so I turned the drive shaft back a tooth or two so that now the cam gears align with the timing pointers at about 5 degrees BTDC.

[narfire]

A few months ago I had something similar. The car went ok but compared to the past,did not have the same zip to it. I really noticed going up hills.
When I put a T light on it ,the timing was around 20 deg btdc, should be 10 deg. When the cams were lined up the crank mark was out.
Took the belt off and got the cams and crank lined up just right,put a new belt on, set the timing to 10 deg. and what a difference. The car pulls great up hills and all through the gears.
Sounds like the belt might have jumped a cog or two. Take the time and get the cams and crank set up at 0 deg and put a new belt on. set the timing up then to 10 deg. Hopfully that will cure the issue,othere than parking the car on the street

[zachmac]

at TDC, the cams were a little behind. at about 5 degrees past TDC the cam gears aligned with the timing pointers, so I turned the drive shaft back a tooth or two so that now the cam gears align with the timing pointers at about 5 degrees BTDC.

I am a little confused. First, when you say 5 degrees I assume you are talking about the crank pulley. Realize that the crank turns twice as fast as the cams so 5 degrees there is 2.5 degrees on thecams. Now the cam drive gears as far as I can tell by a quick count of 1/4 circle are 48 teeth. That means each cam gear tooth / notch is about 7.5 degrees of cam timing. Therefore with stock factory cam drive gears you can only "adjust" cam timing in 7.5 degree increments. Are you saying you set your crank to 0 degrees TDC and then moved each cam one tooth? If so then you changes cam timing by 7.5 degrees. If you moved them two teeth you changed cam timing 15 degrees.

Please someone jump in if I am wrong here. Also, everything I say next is off the cuff and also needs to be vetted by someone who knows without thinking about it or has time to think about it.

Next, the advancing or retarding of exhaust versus intake cams have very different effects. I you advance an exhaust cam you are opening the exhaust valve sooner and getting to full closed sooner as well. That means you are depressurizing the combustion pressure sooner (shorter power stroke before exhaust valve starts to open and relieves combustion pressure) BUT you have greater pressure pushing the exhaust out so in theory more flow. This assists intake charge during the overlap (both valves open) and again in theory can increase total flow through the engine and make more horse power (at a different RPM and with less torque).

If you advance an intake cam you are opening it sooner in the exhaust stoke and keeping it open less of the intake stoke. This has the effect of REDUCING intake flow as you are fighting a higher remaining combustion pressure (you opened the intake valve sooner in the exhaust stoke). Meanwhile if you advanced both the same amount you haven't changed overlap at all but you've shifted it in the cycle to where you have LOWER flow though the engine.

I believe that if you are going to run other than factory cam timing with stock cam gears you will be much better off with either ONLY the exhaust cam advanced (intake at mark) or for a more radical setup the exhaust one tooth advanced and the intake one tooth retarded.

Again, others please chime in here.