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Chris
Chris, Shop Foreman
Category: Jeep
Satisfied Customers: 13873
Experience:  Jeep Certified Master Tech
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1990 Jeep Wrangler 2.5l manual.... No ground pulse on

Customer Question

1990 Jeep Wrangler 2.5l manual.... No ground pulse on injector. Have good spark , good fuel pressure just no ground to injector from computer ..replaced crank sensor , computer, ignition module, map sensor...this happened six months a go, tried for two weeks to find problem and all
JA: Are you certain it's the fuel pressure sensor that's in need of attention? What about the fuel rail? Have you checked it yet?
Customer: there is no rail TBI system only one injector
JA: Are you fixing your Wrangler yourself? What have you tried so far?
Customer: It happened six months a go changed starter becouse it was cranking slow and out of no where it started, six months later same problem
JA: Anything else you want the mechanic to know before I connect you?
Customer: That's it
Submitted: 4 months ago.
Category: Jeep
Customer: replied 4 months ago.
How long do I have to wait?
Expert:  Chris replied 4 months ago.

Hello and welcome to just answer. Have you verified that there is good continuity on the injector driver circuit between the injector connector and the PCM connector?

Chris

Customer: replied 4 months ago.
I'm reading it right from the pcm, no ground pulse from Pcm....and it happened six months ago and out of no where it jus started running...
Customer: replied 4 months ago.
Now is back the same way
Expert:  Chris replied 4 months ago.

Ok, then you may have a slightly spread terminal at the PCM connector, or at the injector connector. Do you have access to an OBD 1 scan tool that can check for codes or look at sensor data? If not can you rent one?

Chris

Customer: replied 4 months ago.
I'll get one and take a look at the sensor data, don't believe is a spread terminal at pcm or injector. I'm directly touching the leads , what sensor other than crank sensor could pcm need to pulsate the ground?..... I once had a o2 sensor shorted that wouldn't let the vehicle run... Not sure if that would be the case now
Expert:  Chris replied 4 months ago.

Okay, besides the crank sensor, the cam sensor in the distributor will affect the injector ground pulse, You may want to check that.

Chris

Customer: replied 4 months ago.
There is no cam sensor , no plugs out of distributor
Expert:  Chris replied 4 months ago.

This is a 1990 right?

Expert:  Chris replied 4 months ago.

It should look like the picture in the link below.

Chris

Customer: replied 4 months ago.
No... That's 91 n up, mine is a 90 does not have it
Customer: replied 4 months ago.
I did notice that the tach and Gage's fuse is burned and every time I put one on it blows, it did that before it stopped running it may be related, when the fuse blew it still ran
Expert:  Chris replied 4 months ago.

You are right my mistake. 91 and up. Okay, then the crank sensor on that engine provides a signal to the PCM for spark and fuel injector pulse. The MAP sensor will determine how much the pulse should be. Try disconnecting the MAP sensor and see if it will run.

Chris

Customer: replied 4 months ago.
Ok I'll try
Expert:  Chris replied 4 months ago.

Ok, I may be off line for a couple of hours, but will check back later.

Chris

Customer: replied 4 months ago.
Ok thank you
Expert:  Chris replied 4 months ago.
You are welcome! I am back now.
Chris
Customer: replied 4 months ago.
Tried the map sensor and nothing no change
Customer: replied 4 months ago.
I think next I should check every ground and power going in and out of the pcm to see if there anything missing
Customer: replied 4 months ago.
What do you think.
Expert:  Chris replied 4 months ago.

Yes, at this point probably a good idea. I would send you a wiring diagram, but I only have the older diagrams at work. If you need it, I can send it to you next week.

Chris

Customer: replied 4 months ago.
I have a few .. Ill do it tomorrow , frustrated for today
Expert:  Chris replied 4 months ago.

Gotcha good luck, and I will look for your reply tomorrow,

Chris

Customer: replied 4 months ago.
Ok
Expert:  Chris replied 4 months ago.

.............................

Customer: replied 4 months ago.
Don't know if it means anything but key on I have ground at pin 21 from the computer to injector but at crank turns to 12v power... That can't be right..?i put a Snap on test light that reads volts, lead to ground and touching the light blue wire that goes to injector and it reads 12v
Customer: replied 4 months ago.
On crank
Expert:  Chris replied 4 months ago.

Well that is normal because the ASD relay will send 12 volts to the injector, through the injector coil, and if the PCM is not grounding the injector, you will see 12 volts. If the PCM grounds that circuit, then the voltage reading on that circuit will be zero.

Customer: replied 4 months ago.
There is one other problem that may be related when I bought the jeep the fuse for the Gages and tach kept blowing every few months, now it's completely shorted , as soon Asian put a fuse in it blows, it has been like that for around 7 months , the jeep was running with that fuse blown so did not think it was related.
Expert:  Chris replied 4 months ago.
What is the actual fuse number?
Customer: replied 4 months ago.
Is that last one with 15 amp fuse, don't know the #
Expert:  Chris replied 4 months ago.

Ok I see it. That should not really cause the no injector pulse if that fuse blows based on that diagram. Something else is causing the no injector pulse.

Customer: replied 4 months ago.
Any other suggestions ?...if the wires from map sensor to pcm are shorted could that tell he computer not to fire ground?
Expert:  Chris replied 4 months ago.

Yes, That can and will cause a no injector pulse. Have you disconnected the MAP sensor connector and PCM connector, then check for a short to ground in that circuit?

Chris

Customer: replied 4 months ago.
I just disconnected the map before
Customer: replied 4 months ago.
How do I check for short ? ohms?
Customer: replied 4 months ago.
Sorry if am asking stupid questions but my brain is fried with all of this
Expert:  Chris replied 4 months ago.

Ok, well check for a short by disconnecting PCM and MAP sensor, then set your meter to ohms, ground the black lead of the ohm meter and then probe the map sensor terminals one wire will show continuity, but the signal wire should not. If it does, then that circuit is shorted to ground. Try that and get back to me.

Chris

Customer: replied 4 months ago.
I got something,all three leads a MAP connector show nothing.... At least one should right?
Expert:  Chris replied 4 months ago.

Well actually if the PCM connector is disconnected then you should have no continuity to ground. If you plug in the PCM then you would see continuity.

Chris

Customer: replied 4 months ago.
Any other suggestions?
Expert:  Chris replied 4 months ago.

At this point, it is time for a scan tool to help us diagnose this. The Snap On MT 2500 would be a good one to use on your Jeep, but you will also need the appropriate adapter to connect to the data link connectors under the hood. See if you can get/rent one and then get back to me.

Chris

Customer: replied 4 months ago.
Ok I will
Expert:  Chris replied 4 months ago.
Sounds good.
Customer: replied 4 months ago.
Hi chris got a snap on solus edge
Customer: replied 4 months ago.
Customer: replied 4 months ago.
The white part says throttle % 0
Customer: replied 4 months ago.
The white is erg on
Customer: replied 4 months ago.
That's all the data at crank
Customer: replied 4 months ago.
I don't understand why rpm says 303 if it's not running and it does not move at crank
Customer: replied 4 months ago.
Sorry all the data is key on on those pic if u need cranking pic of dada I have those as well
Customer: replied 4 months ago.
Customer: replied 4 months ago.
Customer: replied 4 months ago.
Three
Customer: replied 4 months ago.
The last three pic where cranking
Customer: replied 4 months ago.
tps says 0 volts and throttle 0 %
Expert:  Chris replied 4 months ago.
Hmmm, if you disconnect the crankshaft position sensor, does the RPM still show 304 when you are not cranking?
Customer: replied 4 months ago.
I'll try it tomorrow around 1pm
Customer: replied 4 months ago.
Actually yes on the first pic , that's just key on
Customer: replied 4 months ago.
The forth pic is cranking
Expert:  Chris replied 4 months ago.

Okay, check it with the sensor disconnected. I will look for you tomorrow.

Chris

Customer: replied 4 months ago.
Ok try
Customer: replied 4 months ago.
Thank you
Expert:  Chris replied 4 months ago.

You are welcome!

Customer: replied 4 months ago.
Ok data shows 0 on crank sensor disconnected , and303 cranking
Customer: replied 4 months ago.
Connected
Expert:  Chris replied 4 months ago.
with the crank sensor plugged in, and the key on you get 303?
Customer: replied 4 months ago.
No now I got 0 key on plugged in.... Maybe it was computer being slow with the data yesterday
Expert:  Chris replied 4 months ago.
Ok that is probably what it was. Tell me, will it try to start if you spray some throttle body cleaner into the throttle body?
Chris
Customer: replied 4 months ago.
Customer: replied 4 months ago.
Plenty of spark
Customer: replied 4 months ago.
This happened 6 months ago and I went nuts trying to find the problem, I felt that the starter was cranking weird so I changed it coulee I was going to be a problem anyway, and after a few attempts it started and ran this long... I know starter is not the solution but thats what happened last time
Expert:  Chris replied 4 months ago.

This is a strange one indeed. let's back track a bit. If you disconnect the injector connector, and the PCM connector. Use your ohm meter and place one test probe from the meter onto the injector driver terminal at the injector connector, and the other test probe onto the corresponding injector driver terminal at the PCM connector. Tell me what the resistance reading on the meter is.

Chris

Customer: replied 4 months ago.
Ok out of work and I can devote time to the jeep.....000.3
Expert:  Chris replied 4 months ago.
Ok
Customer: replied 4 months ago.
Ohms for that wire were 000.3
Expert:  Chris replied 4 months ago.
Oh ok that is good. I am starting to think that the problem is with the PCM
Customer: replied 4 months ago.
I'll put another one on later around 1..... I have two
Customer: replied 4 months ago.
I already did that and same results
Customer: replied 4 months ago.
What are the chances of having two bad ones with the same problem?
Expert:  Chris replied 4 months ago.

It is not common, but I have seen that before. I will look for your reply today.

Chris

Customer: replied 4 months ago.
No change with the second computer, do you think I should try a third?
Expert:  Chris replied 4 months ago.
Where are you getting them from?
Customer: replied 4 months ago.
I have two... Original one and one from advance auto parts rebuilt
Customer: replied 4 months ago.
Should I get another
Expert:  Chris replied 4 months ago.
At this point I say try another one.
Chris
Customer: replied 4 months ago.
Ok ill get back to you after I find one, hard to find this old
Expert:  Chris replied 4 months ago.

I know.. Good luck and keep me up to date!

Chris