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Back again with the 1987 Toyota Cressida, 5MGE engine 80k miles on it. The car sat for a year, thought it was an issue with fuel going bad, but topped off with fresh fuel and still kept having issues where the car would not turn over, or if I did get it to turn over it would run very very rough then die. Finally it dawned on me, maybe the vane air flow meter had an issue, so I tried propping the door open and what do you know? The car started and stayed on, issue was fuel was running very rich almost jet black exhaust. Had to move it a few weeks ago, they were coming to seal coat my street. While it was at my brothers place a mile down the street it ran ok, still rough since the VAF was acting funny. Then when it was time to bring the car back home, the battery was dead, jump started, had it running for a moment actually was running smoother than usual jumped in the car ready to go and it died. Would not turn over, battery died again due to constantly trying to start, again and again finally jumped it and would only stay on if I help the throttle down if I let up the car would sputter and die. Put 2 gallons of fresh fuel just in case it was flow from running so rich no luck there. Really confused as to what can be the issue, do I need to replace the VAF? Or is there something else I need to check on? From what I can tell there does not seem to be any air system leaks. Attached some youtube clips of before and after I found out propping the VAF door open would keep the car on. Apologize for the run ons using phone to write this out.
Before I thought to prop the VAF open
After
After
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Measure output voltage of the MAF. Typical vane type MAF is about 1.2 to 4.9 volts. Higher = more air. Idle voltage is typically 1 to 1.5v.
If you have access to a scope it would be useful to graph the voltage as you open the vane manually (KOEO) to look for dropouts in the signal. Engines that spend lots of time idling can develop dead spots in the potentiometer operated by the vane.
Rick
What I’m seeing is the fuel pump is only powering on if the VAF door is all the way open. The car use to stay on so long as the VAF was open and would idle now it will only stay on if the throttle is being pushed as well. I have no way to read the voltage though.
You can get a simple Digital Volt/Ohm Meter (DVOM) from any discount tool store. Harbor Freight has them for $9.99. Then you just need a wiring diagram and some stick pins (the T shaped ones) to back probe the sensor harness. Without checking some voltages it’s anybody’s guess as to what might be going on. You’ll have to do some diagnostic testing. I’m doubtful that you can buy those MAF’s anymore (maybe check on Rockauto) but I’m sure they are expensive if you can. It may very well be the problem but don’t “troubleshoot with Visa”. Know a part is bad with 99% probability before you buy it. The fact that the fuel pump only runs if the MAF is wide open would seem to indicate the fuel pump circuit is being triggered by a voltage reading from the MAF and the ECU in turn powering up the fuel pump relay. That also points to a possible voltage reading problem with the MAF signal but I’m only speculating at this point. Early fuel injection systems employed a variety of mechanisms to detect engine cranking/running to trigger the pump and that’s probably one of them as most of those vane MAF systems didn’t control ignition from what I recall.
Rick
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