Popping through intake, bucking, missing... major FI problem like I have never seen.
- Thread starter Slow LX
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bullitstang1313
Member
One question, why do you have the idle at 1800 rpm? It sounds like you have a vacuum leak still.
Glad to hear you got it sorted out...
However, can anyone explain to me how a bad MAF sensor caused low a low vac signal?
I don't get this at all, so I must have missed something really basic?
Slow LX - Can you provide some more details on the MAF/MAS you used that didn't work, and the one that did work?
Were they 'calibrated' aftermarket?
Stock Ford?
Other?
I just don't see how the MAF could have caused the vac problem.
If I don't ask I will loose sleep over it for the next week.
jason
This thing effected everything, the truck was idling at 800 rpm very rough, pulling 5-6'hg of vac, but when I put the good meter in it jumped to like 1800rpm pulled 18-20'hg (at 1800rpm) and the extreme rich smell went away.
They were all factory for 55mm mass air's for 19# injectors...
They were all factory for 55mm mass air's for 19# injectors...
dragnazz5.0
My "0" key d0esn't w0rk, s0 I have t0 use the zer0
please throw away that analog multimeter and get a good dvom. most analog meters have very little internal resistance like jrichker said. and most dvom's have 10 million ohms of internal resistance....so you can check computer circuitry without overloading the circuit and letting the smoke out of the computer
Glad to hear you got it sorted out...
However, can anyone explain to me how a bad MAF sensor caused low a low vac signal?
I don't get this at all, so I must have missed something really basic?
Slow LX - Can you provide some more details on the MAF/MAS you used that didn't work, and the one that did work?
Were they 'calibrated' aftermarket?
Stock Ford?
Other?
I just don't see how the MAF could have caused the vac problem.
If I don't ask I will loose sleep over it for the next week.
jason
Vac is basically a side-effect of the power of the motor. Vac actually works against a motor running. The more power you're making at idle the more Vac you're going to pull. You can actually set "power" timing by using a vaccum guage and setting your timing to whatever gives you the most vaccum.
His motor was running so crappy and making so little power due to being rich I suppose that it couldn't pull more than 5-8 inches.
Jason wanted to know how a MAF affected the vacuum signal. This was an answer I was waiting for - I don't buy it.
I consider the cam specs and sealing abilities inside the motor to be far and away most crucial in determining a vacuum signal.
I consider the cam specs and sealing abilities inside the motor to be far and away most crucial in determining a vacuum signal.
Hook a vac gauge to your motor and fiddle with the timing while she's running. You'll see the vaccum change with the timing. Another thing you can do is pull the VAC line off the FPR so you're running rich at idle and watch the VAC drop because the motor's out of tune and making less power. (plug that fpr vac line)
I would agree the drastic changes he experienced is hard to swallow for just a MAF problem, but I'm also not there with it infront of me so I don't really have a leg to stand on to call b.s.
Not exactly. Vac is related to rpm and throttle position. Not really power.
WOT is the most power you will get at a given rpm, yet it is the lowest vac you will get at that rpm.
Power doesn't directly influence the vac signal.
Only rpm and throttle position can impact the vac signal.
I have set timing this way before.
I still can't see any way that running rich would result in numerically lower vac signals.
What happened with the vac when you re-set the idle speed?
Where is the vac now?
Yet the MAF signal was so far out of whack that it affected engine vac.
You can see how I would be asking questions...
I hope I don't come off as argumentative.
I am just trying to understand how the MAF signal can cause the problems you experienced.
My (somewhat limited) knowledge of the EEC tells me that when a sensors output falls outside the range of 'normal' values, the computer ignores that signal, and adopts a back up control strategy.
I would think that a MAF signal that far out of range would have caused the car to go into OL, running off tables.
I just don't get it, but I do want to understand this.
I have always felt that you can learn more from the unusual problems, than from typical issues.
Yes ofcourse vac is most affected by throttle position and rpm. His issue as he describes it would have affected his idle rpm and subsequently his vac.
A more effecient combustion in the cylinder results in more power from that combustion. If you have two engines, *all other things being equal* but one is idling richer than the other - therefore reducing the efficiency of the combustion resulting in less power at idle, that idle is going to be reduced because the power is reduced, resulting in less VAC.
This is the relationship I'm talking about.
But like I said before, the massive difference is hard to swallow.
I get what you're saying.
If a poor running condition causes the idle speed to decrease, then the vac will fall off.
However, it seems to have been forgotten that he had adjusted his idle rpm.
What I am saying is that if he had 8" of vac at idle while at 800rpm with a bad MAF,
then he should have 8" of vac at idle while at 800rpm with a good MAF.
Power or efficiency don't come into play.
Vac signal is a function of the cubic inch displacement, engine speed, cam timing, and throttle position.
There is no need to be discussing power...
The fact that the idle (throttle position) was adjusted (most likely with the set screw), may have an impact on the engine vac, but only 1-2", 3" at the very most.
Thanks for humoring me guys.
This is an interesting topic.
:Word:
I completely agree, i only mention power at idle in how it will vary idle rpm to cause the change in vac like you say.
I'm just seeing that now he's idling at 1800rpms and getting his ~20 inches, was 800rpms earlier with 5inches? assuming throttle position hasn't changed, i can believe the increase in vac with that much increase in rpm.
1800 isn't exactly right though, so I think there's more going on than just a bad MAF.
globaltefl
Member
5.0 runs very inconsistently
QUESTION!
Why does 90 5.0 run great as it is warming up and terrible when it is at normal op temp??
When I start it, it dies, then next time it will run and idle a little rough. If I try to drive it right away it pops in the manifold. But after a couple minutes it runs strong through the whole rpm range.
BUT when it is hot or normal operating temperature it will run really badly, esp after I shut the car off and come back a few minutes later. I have new plugs, new distributor, new coil, new O2 sensors and new IAC valve. I have checked the voltage on all the sensors except the EVR and everything seems normal. I get a 41 and 91 code, which seems now to point to a vacuum leak.
QUESTION!
Why does 90 5.0 run great as it is warming up and terrible when it is at normal op temp??
When I start it, it dies, then next time it will run and idle a little rough. If I try to drive it right away it pops in the manifold. But after a couple minutes it runs strong through the whole rpm range.
BUT when it is hot or normal operating temperature it will run really badly, esp after I shut the car off and come back a few minutes later. I have new plugs, new distributor, new coil, new O2 sensors and new IAC valve. I have checked the voltage on all the sensors except the EVR and everything seems normal. I get a 41 and 91 code, which seems now to point to a vacuum leak.
Start your own post and don't piggyback on this one, and I will try to help you. You may have some wiring problems.
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