Lack of and intermittent power

[robhaynes]

I'm having a heck of a time figuring out what is wrong with my 1980 FI 2000. Symptoms are all over the place. It started with the engine bogging down when it was cold, but then OK when warm. I figured I could live with that. But a few months later, even when warm, with hard accelerating the power is uneven. Now it occasionally stalls when I come up to a red light and is hard to start, and then suddenly its OK again. On the freeway it bogs sometimes when you push the accelerator. Other times its fine. I've been thru the BoschL.pdf diagnostic manual and have found nothing wrong (you know, checking temp sensor, resistance between leads at the computer for various sensors, vacuum and mechanical advance). I even took off the cold start valve to see if it was leaking. Since it seems to be getting progressively worse, I was hoping that whatever it is would totally fail and I could find it. It sure seems like ignition to me. It has new wires, cap, roter and plugs. The mag pickup is about a year old. The car has 100k on it. I've been thinking about getting Allisons electronic distributor, but I'd sure hate to spend that kind of money and not have this issue fixed. It could be the AFM, but I don't want to replace that unless I really need to. I don't think the distributor needs a rebuild, because its not leaking and the timing is dead on (it doesn't jump around like you would expect if the shaft is loose). I haven't checked the coil, but the timing light is really steady at idle so would be surprised if its that. I'm not sure where to go next.

[So Cal Mark]

I'd look closely at the air intake boot for cracks, then see if the AFM flap sticks at any point in it's travel. Have you checked fuel pressure and volume? I doubt your problem is ignition related from the description you gave

[aj81spider]

+1 on the rubber air intake tube. I had those symptoms and it turned out the intake was cracked under the little nipple that comes out the side. Most of the time it was fine, but once in a while it would flex and I'd lose power.

[spider2081]

After air intake I would check fuel pressure in the fuel rail. I bought a test kit at Harbor Freight and then tested the accuracy of the gauge with a master gauge at work. I was surprised how accurate the HF gauge was. Have you changed the fuel filter lately? How about the rubber fuel lines are they original??

[NSFIAT]

Same issues on my '81 and it turned out to be crud from the fuel tank getting caught up in the fuel pump. I replaced the tank as well as the pump and installed a clear filter between the two to keep an eye on things.

[robhaynes]

I've checked fuel pressure and the AFM flap is free. How do you check fuel volume? The pump is suspect since it is a cheap eBay special. I have about 6k on it and I replaced the fuel lines, filters, cleaned the injectors, and sealed the gas tank at the same time.

Someone told me about how you can use smoke to see where intake leaks are. Watch for where it gets sucked in. Anyone know how to do that? I was thinking I'd use dry ice. When I had the intake boot off for a valve adjustment I checked it pretty thoroughly but I could have missed something.

[micbrody]

I have 81fi. My major issue was intermittent start. I went through entire system. Of course, the last thing I checked was pressure at fuel rail. Pressure was all over the place every time checked ; never over 39, but frequently in 20's; sometimes even below that.(I borrowed fuel pressure gauge from Autozone; pressure readings so variable, I thought that maybe I had bad gauge.
I figure either bad pressure regulator or fuel pump (or clogged filter or clogged tank line). I hooked up gauge (t piece inline) just after pump. Sometimes pressure was normal sometime low. While pump running, I clamped fuel feed to fuel rail to see if pump could generate pressure. It usually did not. After reading about the pumps, I theorized that although pump could pump fuel, could not consistently at operating pressure (in the high 30's). Maybe internal fuel pump check valve bad. Pump was also very noisy (high pitched hum). Since it was not serviceable, I ordered Bosch pump on Amazon for about $75. Hooked it up. Everything great ! Rarely doe the car not start on ignition

[robhaynes]

How do you check fuel volume?

I changed my fuel pump pre-filter.

[robhaynes]

Nobody seems to be reading this thread, but I'll continue to post in case someone does.

I pulled the fuel line between the rail and the cold start valve and pumped for a minute into a gallon container. It was 3/4's full, so that's about 2.5 liters. I've been told the factory spec is 1.5 to 2, so volume seems fine.

So now I'm at a loss as to where to go next. The intake boot seems fine no cracks or apparent leaks.

[TimpanogosSlim]

The smoke test for air leaks is a thing they do on forced induction engines. You look for smoke coming *out of the leaks.

On a naturally aspirated engine you treat it like any other vacuum leak and spray some kind of fuel near possible leaks - whether that's shots of an aerosol of one sort or another or an unlit torch head venting propane, isobutane, etc. When the engine races you found the leak.

Since this is the EFI engine, you should familiarize yourself with L-Jetronic by reading Brad's excellent guide and/or the official Bosch technical manual for L-Jet found here: http://www.cardiagnostics.be/-now/Educa ... Manual.pdf

The main thing is the air meter but it also uses signals from the o2 sensor and a coolant temperature sensor to adjust fueling.

[Yadkin]

I'm not familiar with the specifics of this particular EFI system, but the OP symptoms would point me to electrical issues with the injectors. Try cleaning the electrical connectors first. If the injectors are old, replace them.

[RRoller123]

I would suggest that you check the temp sensor at the coolant T union, both for connector quality and temp sensor reading. The temp sensor is measured back at the ECU main connector under the glove box, and ohm readings vary as the engine warms up. Measuring it back there tells you if the wiring is good getting the signal back from the sensor to the ECU. The coolant Temp sensor tells the ECU to enrich a cold motor. Easy peezy to check with an ohm meter.

This is from Brad's book:

below 14F: 7,000 - 12,000 ohms
@68F: 2,000 - 3,000 ohms
@176F: 250 - 400 ohms

Measured at terminal 13 of the ECU, taken to a suitable nearby ground.

A bit more:

This is from IAP's web site for the temp sensor in the coolant T, provides a little bit more resolution, if you are going to test on a stove top. If you do test on a stove top, use an old pot and THROW IT AWAY after the sensor is immersed in it.

Temperature Resistance
(deg F) (ohms)
14 7,000-12,000
68 2,000-3,000
122 700-1,000
176 200-400
185+ Less than 200

[robhaynes]

Thanks for all the suggestions, I figured it out. I went back and rechecked some of the earlier things, like does the flap on the AFM move freely. It does when I push it with a screw driver from the boot side of the AFM so I thought it was ok. But I pulled the top off the AFM moved it from the clamp on top. Screech. The flap was rubbing on the side. In fact, it was binding at times. I sanded the area with 150 grit until it moved freely, although still rubbing a little and took it for a test drive. Whoa, its back to fun driving. I suppose I should sand a little more until it doesn't rub at all and is completely free.