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sputtering and dying problem

XJRunner

NAXJA Forum User
Location
San Diego
my 87 cherokee is havin issues. When i come up to a stop it spputters and doesnt want to idle. It sometimes dies too. I think it might be a weak fuel pump. I had my friend scan it (OBD) and he said the engine is screaming for more fuel at all rpm ranges but it has the correct pressure at the rail(we checked). What do you guys think?


Engine specs:
89 4.0
comp cam
comp lifters
.060 over bore
borla header
Auto Precision injectors
 
Your friend must be a Magician to be able to get fuel flow information from a 1987 OBD1 system? To mu knowledge, OBD1 is not capable of providing that type of information due to the computer limitations.

Besided unless you ran your rig at al speeds on a chassis dyno with the correct sensors connected, to detect a lean condition at speed or at a certain RPM range, you are only guessing.

You definately have a fuel pressure issue: But the question is: Is the fuel pressure bleeding off, or insufficient?

The early XJ's placed the fuel regulator in the fuel tank with the fuel pump. It was not until 91, when Jeep moved the regulator to the fuel rail.

If your rig is stalling at low speed but seams to run ok off idle, then you are bleeding off fuel pressure. A couple of things cause this. Worn fuel injectors, or worn regulator.

Worn injecotrs can stick and not completely close at idle, so running at idle your rig is litterally bleeding off gas pressure rather than anomizing the fuel into a fine sream. A worn regulator lowers the operating pressure to your fuel rail.

If your fuel rail has a pressure tap at the top, some of the older Renix, do not, you can install a fuel pressure gauge and take e reading. I believe it should be between about 40 PSIG at the rail, running. Don't worry if it's about 3 to 5 PSIG lower. Run your rig for about 10 minuts while observing the gauge.

Now shut you rig off and watch the gauge. The pressure should fall of slightly by a couple of punds then hold steady, if the pressure bleeds off. You have confirmation that your fuel system is at fault.

Start with the injectors, either change out the old ones for some OEM injectors that have been professionally cleanded or install a set of FORD 19# injectors as an upgrage.

But I would change out the regulator and possibly the pump anyway considering the ones from 86 to 90 were prone to failures and could leave you stranded in the trail or along the highway some day. Cheaper than calling a tow truck.

Hope this helps? See ya on the trail.
 
Your friend must be a Magician to be able to get fuel flow information from a 1987 OBD1 system? To mu knowledge, OBD1 is not capable of providing that type of information due to the computer limitations.

Besided unless you ran your rig at al speeds on a chassis dyno with the correct sensors connected, to detect a lean condition at speed or at a certain RPM range, you are only guessing.

You definately have a fuel pressure issue: But the question is: Is the fuel pressure bleeding off, or insufficient?

The early XJ's placed the fuel regulator in the fuel tank with the fuel pump. It was not until 91, when Jeep moved the regulator to the fuel rail.

If your rig is stalling at low speed but seams to run ok off idle, then you are bleeding off fuel pressure. A couple of things cause this. Worn fuel injectors, or worn regulator.

Worn injecotrs can stick and not completely close at idle, so running at idle your rig is litterally bleeding off gas pressure rather than anomizing the fuel into a fine sream. A worn regulator lowers the operating pressure to your fuel rail.

If your fuel rail has a pressure tap at the top, some of the older Renix, do not, you can install a fuel pressure gauge and take e reading. I believe it should be between about 40 PSIG at the rail, running. Don't worry if it's about 3 to 5 PSIG lower. Run your rig for about 10 minuts while observing the gauge.

Now shut you rig off and watch the gauge. The pressure should fall of slightly by a couple of punds then hold steady, if the pressure bleeds off. You have confirmation that your fuel system is at fault.

Start with the injectors, either change out the old ones for some OEM injectors that have been professionally cleanded or install a set of FORD 19# injectors as an upgrage.

But I would change out the regulator and possibly the pump anyway considering the ones from 86 to 90 were prone to failures and could leave you stranded in the trail or along the highway some day. Cheaper than calling a tow truck.

Hope this helps? See ya on the trail.


Some misinformation here.

First of all, Renix is Renix. It's not OBD-1

The fuel pressure regulator IS located on the fuel rail.

All Renix Jeeps have a fuel pressure tap on the fuel rail.

The pressure reading should be 31 PSI sith the vacuum hose connected to the FPR, 39 with it disconnected.

And, anything below that IS a concern.
 
Your friend must be a Magician to be able to get fuel flow information from a 1987 OBD1 system? To mu knowledge, OBD1 is not capable of providing that type of information due to the computer limitations.

Besided unless you ran your rig at al speeds on a chassis dyno with the correct sensors connected, to detect a lean condition at speed or at a certain RPM range, you are only guessing.

You definately have a fuel pressure issue: But the question is: Is the fuel pressure bleeding off, or insufficient?

The early XJ's placed the fuel regulator in the fuel tank with the fuel pump. It was not until 91, when Jeep moved the regulator to the fuel rail.

If your rig is stalling at low speed but seams to run ok off idle, then you are bleeding off fuel pressure. A couple of things cause this. Worn fuel injectors, or worn regulator.

Worn injecotrs can stick and not completely close at idle, so running at idle your rig is litterally bleeding off gas pressure rather than anomizing the fuel into a fine sream. A worn regulator lowers the operating pressure to your fuel rail.

If your fuel rail has a pressure tap at the top, some of the older Renix, do not, you can install a fuel pressure gauge and take e reading. I believe it should be between about 40 PSIG at the rail, running. Don't worry if it's about 3 to 5 PSIG lower. Run your rig for about 10 minuts while observing the gauge.

Now shut you rig off and watch the gauge. The pressure should fall of slightly by a couple of punds then hold steady, if the pressure bleeds off. You have confirmation that your fuel system is at fault.

Start with the injectors, either change out the old ones for some OEM injectors that have been professionally cleanded or install a set of FORD 19# injectors as an upgrage.

But I would change out the regulator and possibly the pump anyway considering the ones from 86 to 90 were prone to failures and could leave you stranded in the trail or along the highway some day. Cheaper than calling a tow truck.

Hope this helps? See ya on the trail.

not too be rude but your wrong. My regulator is at my rail and the injectors i have are maybe a year old
 
we checked it with the jeep in park through the rpm range, i would have liked to test it while driving but mark(a mechanic friend) had is wife there so we didnt have time. it was good with no load on it
 
So should I replace my pump? I have a spare one out of my old 96

91 and newer fuel pumps for the HO engines are higher pressure, with the FP regulator in the gas tank, so the 96 FP will not work on a renix.
 
my 87 cherokee is havin issues. When i come up to a stop it spputters and doesnt want to idle. It sometimes dies too. I think it might be a weak fuel pump. I had my friend scan it (OBD) and he said the engine is screaming for more fuel at all rpm ranges but it has the correct pressure at the rail(we checked). What do you guys think?


Engine specs:
89 4.0
comp cam
comp lifters
.060 over bore
borla header
Auto Precision injectors

If the problem is only at idle, it is not the fuel pump!

Is the problem only at idle?

If yes, then get the FSM data and a volt meter and test the TPS. The IAC may be sticking, so pulling the IAC from the throttle body and cleaning and lubing it and cleaning the throttle body port it sets in may help. An O2 sensor that is working right at cruise, but not at idle due to loos of the internal heater or voltage to the heater, can cause a rough idle after warm up. Procedures for the above (testing the O2 sensor and TPS, and cleaning the IAC and throttle body) are in old posts here, some with photos just google to find them or use the NAXJA search menu. This will help too.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm
 
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