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tach signal during crank?

Shorty

NAXJA Forum User
NAXJA Memorial Lifetime Member
'91 XJ, 4.0l, AW4

am I supposed to be seeing a tach reading (on the dash) during crank? She cranks all day without any signal. I'm figuring CPS, but haven't checked yet. I'll be checking in a few. but can't remember if there was any signal during crank..... so... anyone with a '91 wanna run out and check for me??

....please?......
 
tested crank sensor- infinite resistance A-B
tested for spark- weak, but available at three plugs (we'll assume the others for now)
tested fuel pump relay- continuity across 30-87 when 85/86 are energized
verified +12V to terminal 30 at fuel pump relay
+12V into ballast and 11.2V out when in run

I'm about to condemn the pump, but will first check:
+12V to terminal 85 (or 86 can't recall) when cranking
bypass fuel filter with fuel hose
+12V at pump when cranking

can you tell momma doesn't want to come out and crank the starter right now?


have I missed something obvious?
any other thoughts?

It run fine yesterday when I shut it off.
 
tested crank sensor- infinite resistance A-B
tested for spark- weak, but available at three plugs (we'll assume the others for now)
tested fuel pump relay- continuity across 30-87 when 85/86 are energized
verified +12V to terminal 30 at fuel pump relay
+12V into ballast and 11.2V out when in run

I'm about to condemn the pump, but will first check:
+12V to terminal 85 (or 86 can't recall) when cranking
bypass fuel filter with fuel hose
+12V at pump when cranking

can you tell momma doesn't want to come out and crank the starter right now?


have I missed something obvious?
any other thoughts?

It run fine yesterday when I shut it off.

I don't see fuel rail pressure test in that list
 
When my rotor on my 98 was busted a couple of weeks ago, the little clip came off, there was no tach crank. I just ran out and tried it, it starts too fast [knock on wood] for me to see but it did not look like it though.
 
I'm gonna throw this thing in the garbage and call it a day!

fuel pressure was zilch, hence the fuel system checks-- I shoulda included that, huh?

long story shortened:

-Jeep sat for 2 years
-ballast was bad- replaced
-started and ran (poorly at first, then better)
-I shut it off two days ago running fine
-tried to start yesterday and no go
-added 2 gal of gas and fired right up
-ran about thirty minutes yesterday- off and on-- shut it off running fine
-went out today- no start (no fuel pressure)
-added 3 more gallons of gas (thanx Harley Davidson) and fired up again.

I'm thinking that there's a butt-ton of junk in the gas tank and it's plugging the in tank strainer ar the pump just plain sux.

anything else I'm missing?
 
neither my '96, nor my '89 show any tach movement while cranking. i vote for some kind of bottom dwelling tank detritus.

yeah, that's my diagnosis at this point too-- I'll probably just change the pump and strainer as good measure when I drain and clean the tank.
 
sending unit was my first thought, but I had put almost four gallons into it and only run it about 40 minutes total before today. I wouldn't be surprised that it was off, but I couldn't possibly have burned that much fuel in 40 minutes. I'm thinking that every time I dump more fuel into it, it sloshes around and removes the chum on the fuel strainer.

I'm still on the fence as to how much trouble shooting I'm gonna do vs. change the pump, strainer and filter and know they're good. They've all got 175000 miles on them and been sitting for two years too.

I've eliminated the electrical gremlins and don't have any problem upgrading 18 year old parts- even if the upgrade is just new vs. old.
 
Why don't you just run 12v direct to the pump, and run the pump out put into a measured container. See if the pump runs, and how much gas you pump in 60 secs?

When you first turn the ign key to "on", you should here the pump run for ~5 sec. This primes the system. When the PCM gets a tach sig from the ignition module during engine crank, the pump should start running again.
 
You going to dump the tank?

that's the plan- pull it, dump it, replace pump and sending unit. If I;m there, I may as well make it all good for another 20 yrs.

Why don't you just run 12v direct to the pump, and run the pump out put into a measured container. See if the pump runs, and how much gas you pump in 60 secs?

It does run sometimes- I was just verifying that it was getting proper input before I dropped the tank when I noticed the no tach signal during crank. The lack of output was an intermittent problem verified by lack of fuel at the rail.

When you first turn the ign key to "on", you should here the pump run for ~5 sec. This primes the system. When the PCM gets a tach sig from the ignition module during engine crank, the pump should start running again.

Always hear the pump prime and usually hear it during crank (more likely that it's always running during crank and I'm going deaf)

There's more than enough fuel in the tank and the pump makes noise, but intermittent 'no fuel' at the rail leads me to believe a stopped up strainer. I'll dig back into it next week, as I'm out of town starting tomorrow.
 
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