code 34...low voltage at MAF....
do I need a new MAF???

code 54, low voltage at fuel pump, or fuel pump relay, or output failure @quad drive module...do I need a new pump or relay??

and what in the hell is a quad drive module....

 

Generating a DTC 34 on an '88 TPI means that the ECM is not getting adequate intake air signal from the MAF while the rest of the system inputs (TPS, RPM) indicate that the intake air rate should be greater. You might need a new MAF sensor. However, since it is the most expensive part in the system, and may not solve the problem, it would be good to diagnose the problem before throwing needless parts at it. As you can probably see, the other sensors involved can also play a role, as well as other components in the induction system. It would be sad to spend $900 for a new Bosch MAF (yes, they are still available, and that's what they cost from Bosch) only to discover that a $10 relay is failing, or the inlet duct is loose or leaking, or that the oil filler cap was inadvertently left off.

The DTC 54 on that same vehicle indicates the voltage in the fuel pump circuit was below 2 VDC for more than two seconds when the pump relay was energized. That could be due to a wiring problem, failing relay, shorted fuel pump, or poor connections at the ECM or pump relay.


Incidentally, the "Quad Driver Module" is a TTL electronic logic gate that drives several real-world outputs, like the EVAP solenoid, EGR solenoid, TCC relay, etcetera. Years ago (late '70s / early '80s), there was a separate module on some vehicles that performed these functions, but it is now all incorporated into integrated electronics in the ECM. The drivers have monitoring that senses a connected load through the voltage drop across an output resistor (shunt). It the voltage across the resistor is too high, the load is presumed to be shorted, and the output shuts down to avoid damage to the module. If the shunt voltage is too low, the ECM presumes the load is defective or disconnected. Either condition can set a DTC. That doesn't necessarily mean that the ECM is defective, only that a connected load is out of tolerance. Usually, the ECM can shut down an output and protect itself before internal damage occurs. The cause is almost always outside the ECM, at one of the load devices or their wiring.

 

whats going on is, when i try to give the car gas, it wants to die....

its acting like its not getting enough fuel, so I am going to replace the pump.....

should i replace the relay, too????

 

If you want to lose more wages, replace the pump. The ECM is trying to tell you that is has a problem with the reported data, not with the fuel pressure.

Even if there were a pressure problem, the pump would be the LAST place I'd look. Test the pressure. That will tell you if the system is making adequate pressure or not. If not, it may not be the pump. There is a pump relay that powers the pump, connectors at teh tank and along the wiring harness, a fuel filter in the system, and a pressure regulator at the end. Any of those could cause low pressure.

And none of that will satisfy the ECMs lack of adequate MAF signal. Is the MAF connected properly? Relays intact? Intake ducts and hoses connected and not damaged? Is ther a breather type oil filler cap installed? Is the EGR leaking?

You can replace the pump if you like, but it's not likely to solve the problem.

 

I was thinking about that myself after you posted.

I have already borrowed a fuel pressure tester to test the pressure....

if the pressure reading drops when i give it throttle, what could be the cause??because that seems to be whats going on. It will idle fine, but when I give it throttle, it stumbles and wants to die like its not getting enough fuel.

correct me if I'm wrong, but wouldnt a faulty relay cause the pump not to even work?? because doesnt a relay just relay power to and from the pump??

the fuel filter is new, changed 2 days ago...

MAF is hooked up, and all ducting seems to be intact, but i will double check that. air filters are new. stock oil cap. EGR seems fine. didnt know there were relays for the MAF, will need to check those.

 

fuel pressure at idle was between 38-40, and raised to 43-45 when i gave it throttle...

disconnected my TPS, and the idle smoothed out dramatically..

disconnected my MAF, and it cured the stumble, and now it will rev to redline smoothly.....

looks like I'm callin NAPA for a MAF tomorrow....

 

As one final test to be more certain, you might want to measure the voltage at the MAF connector to make sure the unit is getting power.

It would be sad to have you drop a couple hundred bucks on a replacement MAF because a $10 relay had failed, or a connection had gone bad.

Your relays should be here:



The MAF should be getting 12 VDC from the power relay, and NO voltage from the burn off relay:



As long as your meter is there, you can also check for MAF output signal while the engine is idling:



If the voltage test results are abnormal, check back with details. If you do need a MAF, I'd suggest getting the thick film type rather than another hot wire replacement. Same or lower cost, and it will last forever.

 

can you explain the difference between the thick film and hot wire....

and where to find them..

thanks for all your help Vader.

 

The original Bosch MAF used on our cars use a hot wire sensing element. The wire is heated electrically to maintain a differential of 75°C between the inlet air of the MAF sampling tube and the discharge air. The amount of current required to maintain the temperature differential is directly related to the amount of heat the wire loses to the air moving through the sensor. The MAF electronics measure this heater current and determine the amount (in mass, not volume) of air that travels through the sensor.

This wire is only slightly larger than the filament of an incandescent light bulb, and has about four supports that keep it in position. It is very fragile, and can be broken by shock, debris, or even the pressure waves created by a backfire. The screens in each end of the AMF sensor are there to help keep out larger debris and deflect the pressure waves created by backfire. Still, the wire is rather easily broken.

The hot wire type MAF will accumulate atmospheric moisture, dust, oils, and other contaminants that will effectively insulate the wire, preventing it from rejecting its heat to the passing air, and skewing the resulting readings. Thus, the MAF must undergo a burn off cycle periodically. The ECM deteremines how frequently based on run time and number of starts. The hot wire element is heated by that same current after the engine is shut off, and reaches an incandescent state (glowing). It is very susceptible to breakage during the burn off. The heating of the wire effectuvely burns off the accumulated contaminants, much like a self-cleaning oven clean cycle.

Most aftermarket MAF sensors are simply remanufactured OEM (Bosch) hot wire sensors. They will work just the same, and are subject to the same failures.

One type that is different is the thick-film sensor. The operation principle is the same (heat rejection measurement), but the sensor uses a film of metal deposited on a silicon substrate as the heating element. It is much more durable, and reacts to incoming air just the same as a hot wire. The only difference is that it doesn't require a burn off cycle to clean debris.

This type is nearly indestructible, compared to the frail hot wire. Originally, this type replacement was offered only by Wells Manufacturing Corporation. About two or three years ago, another company named Micro-Tech made a patent claim against Wells and stated that IT owned the rights to the MAF design, not Wells, even though Micro-Tech did not manufacture or sell a thick film type MAF at the time. Now, Micro-Tech appears to be the only supplier of an aftermarket thick film MAF for our cars, and they are a clone of the 1997 Wells unit.

https://www.thirdgen.org/techbb2/sho...hreadid=332425

What's really odd about this whole situation is that Micro-Tech claimd a patent violation, all while Hitachi had patents on a thick film MAF and was producing them as early as 1991. Strange?

 

great info..thanks!!!

what does the thick film look like inside??

the MAF I just got from Napa has an "M-T" logo on top of the sensor right above the "Flow" direction label.

is that the Micro-tech??

it has a flat board inside with what looks like a brass, or gold colored sensor, and a "u" shaped piece rising up off the board.
it also looks like it might be covered in some kind of film.

I am assuming that I recieved the film type part....

 

The left MAF is a hot-wire type. The right MAF is a thick film type:

 

yup, I got the thick film.....


Thanks for all the advice, Vader, you definitely know your stuff, and it's much appreciated.

btw, I went ahead and got the MAF because of the holiday, but I'm going to check those relays before I install it...

if its just the relays, I can always send it back.