'87 Renix 4.0L Auto: weak vs strong fuel-pump sound when cranking

Last night I almost had to get towed due to following:

Engine cranks over no problem;
ignition spark when cranking no problem.

When cranking but no start, can hear fuel pump buzzing in back and while ignition-key in on-position I crawled under there and sure enough fuel pump was buzzing to point the fuel hoses near the gas tank were slightly vibrating.

Then after the battery nearly drains down to zero I call for a tow while leaving the ignition-key in on-position ... all of a sudden the fuel pump sound goes from "buzzing" to a louder "tick-tick-tick", so I crank with what little battery power is left ... and ... the engine starts right up !!

To me, the problem is possibly not the fuel pump itself since it is ~ 2years old (less than 20K miles), and, with fuel pumps going bad in the past I experienced that they fail to keep the engine idling ... which did not happen here ... the entire 37 mile drive home last night was 100% A-OK (at highway speeds mostly).

So I have been reading this manual today:
http://www.lunghd.com/Downloads_and_Links/Jeep_Renix_Fuel_Injection_manual.pdf
and am now going to start checking:
- connections on the fuel-pump relay;
- connections on the starter-relay (since it feeds the fuel-pump relay);
- connections on the fuel-pump ballast resistor;
- maybe just replace the fuel-pump relay (inexpensive enough).

However, what is not making sense to me is why was the fuel-pump sounding with a "buzz" (and vibrating) when it would repeatedly not start ... what was powering the buzzing fuel-pump if the problem was relay related ... and what "kicked-in" to change the fuel pump sound to a stronger "tick-tick-tick" that then caused the engine to start
(?? is an intermittent ballast resistor failure the problem, or, maybe there is some debris that got stuck in the fuel-pump mechanism ??).

Since maybe dirt in the fuel-pump mechanism I am considering filling-up the 13.5 gallon tank along with a bottle of SeaFoam (if/when I get it started again if I don't find any electrical connection problems).

I am also assuming that since the no-start cranking included strong ignition-spark (no doubt), that the crankshaft position sensor is not the problem ...
... or, maybe I'm wrong on that ?
... with 326K on this '87XJ (it usually runs 100% A-OK) and purchased it with 112K in 1997 I have never changed the crank position sensor ...
... but, when I had to change the crank position sensor on my son's '99XJ couple of year ago, from what I remember those problem symptoms included no ignition spark.

I'll feedback whatever I find over the next couple of days ... in the meantime, does anyone have any suggestions for a problem such as this for a Renix 4.0L 4-speed automatic ?

Checking Fuel flow is a good idea, look for the fuel filter just forward of the rear axle on the driver’s side.
If fuel is not even getting to the inlet side of the fuel filter it will never make it to the fuel rail.
Keep us posted of progress.

When fuel filter is located remove the rubber hose between fuel tank and the filter, extend this hose with additional hose into some sort of container and secure this hose to the container.

Next turn the ignition switch to the on position wait for fuel pump to complete its priming cycle, turn off switch then look in the container for a realist amount of fuel. If realist amount is noted reconnect supply hose remove discharge hose from fuel filter and repeat test.

If small of fuel is noted on either test you are on the right track to correcting fuel delivery problem.

There is also a filter sock on the intake of the fuel pump.

A rubber hose connected to the fuel pump inside the tank that has been going soft on some XJ which will deplete fuel flow.

This could very likely be a fuel pump problem. Just because you replaced it a couple of years ago does NOT mean that it can't fail. I've had fuel pumps fail in a day, a week, and even ones that didn't work out of the box (especially anything made by Airtex). The difference in fuel pump noises you were hearing may be a clue that the pump is starting to fail.

Of course, verify all connections to the fuel pump. And always good to have a replacement relay on hand regardless, so can try that quickly. And get a new filter in there if it's been a while; takes about 15 minutes to change it out on an 88.

I you have access to a fuel pressure gauge, check pressure at the fuel rail. For an 88, you should have 31 psi at idle, then it should jump to 39 psi when you remove the vacuum line to the fuel pressure regulator. Needs to be around that 31 psi range FOR the engine to start.

The ballast resistor could be jumpered to remove that from the equation, but this doesn't sound like a B.R Normally when they fail, the engine will start when the key is in the full START position, (the B.R is bypassed in this position), but the engine will die as soon as you let off the key and the key returns to the ON position.

But don't rule out the pump...............

Get a fuel pressure gauge, and test the fuel pressure at the rail. It should pump up to at least 31 PSI before cranking, and hold steady before cranking, after the buzzing stops.

CPS (CPK), and Ballast resistor are not the cause. You need to check and see if the fuel injectors are opening while cranking. A noid light and remote crank will work, or use a stethoscope tool (long screw drive also works) to listen for clicking fuel injectors. FSM shows how to use a multi meter (volt/ohms) to check the fuel injector firing signal.

Check the oil for signs of gasoline!!!


Last 2 times I thought the fuel pump had died on my 87 and 89, it was poor grounds and poor connections at the >20 year old QC and ground connections near the gas tank.

Thanks for all your quick replies ... here's what I found and did over the past couple of days ... encountered a couple of surprises (at least to me) along the way.

Surprise #1:
regardless this is an '87XJ and the manual link that I included in my first post is for 87-90 Renix, there is:
A) no ballast resistor on the driver's side engine compartment (yes, the aux-fan relay and EGR solenoid are there), and,
B) no connector point of any kind on this '87XJ Starter Relay for a fuel pump ballast resister (the other 3 push-on connector points shown in the manual's Figure 19 are on this '87XJ Starter Relay).

Surprise #2:
the manual's Figure 28 shows 4 relays ... and yes, there are 4 relays in that location on this '87 ... but ... when I removed each relay one-at-a-time then the engine started and ran A-OK ... so ... I'm a bit confused as to whether or not there is a fuel-pump relay in the electric ciruits for this '87 ... at least it looks like 1 of those 4 relays in NOT in-series with the fuel pump.

Here's what I did:
since I was in there, for the 4 relays I sprayed electronic cleaner into the 16 connection slots and cleaned-off the relays male connectors along with putting a light wipe of bulb-grease on those connectors.

I also spray-cleaned the Starter Relay's 3 push-on connectors and then wiped-on JB Ox-Gard to those terminals ... also ... added some sliced length-wise vacuum tubing over the Starter Relay's ignition wire where it traveled-over the metal-bracket (for the 4-relays cover) ... and added some vacuum tubing over the Starter Relay's Starter Solenoid female connector (for whatever reason did not have an insulator cover on that connector and it was only a few millimeters away from the large Battery Terminal connector ... more so since a number of years ago I had run 6ga cable from the alternator to that point terminating with a large lug on the end of that 6ga cable).

I then shot electronic cleaner into the steering wheel housing's slides (somewhat easy since part of the steering wheel bottm-side cover fell off few years ago) ... with the idea that at least part of the ignition-switch connectors would be hit with the cleaner run-down ... followed by shooting some silicon spray into the same locations (after the quick-drying cleaner dried).

Along with doing the above, at each step I would attempt to start the vehicle and ... also surprising ... regardless whether the fuel-pump sound was "weak" or "strong" the engine would start and run (except for when any of the Starter Relay's 3 push-on connectors were removed) ... in other words: all of the more than dozen attempts to start were successful (which is the usual 100% success rate, except for this past Friday night when the success-rate was near-0).

Last step for this weekend: added 2+ gallons gasoline to get to a half-full tank level (13.5 gallon tank) along with added 3+ ounces Lucas Oil Fuel System Cleaner (I have a large bottle of that stuff that I use infrequently on the family vehicles) ... then took it for a test-drive for ~ 25 miles and I have to say that acceleration feels a bit more zippy than prior.

The thought I had about adding in the Lucas Oil Fuel System Cleaner (instead of SeaFoam) was for possibly lubing both the fuel-pressure regulator and fuel-pump internals.

I had changed the fuel filter about a month after the fuel pump was changed couple of years ago (~ 20K miles ago).

My plan now is to drive the '87XJ only locally for a week or 2 (which should include a higher amount of shut-downs and start-ups since it will be for local stuff) ... I'll see what happens.

If there are any failures-to-start that occur again within the next couple of weeks, then I dig some more and post-back what I find.

87s did not have the ballast resistor. I know the 89s did.

One of those 4 relays is the fuel pump relay on my 87!!!! So you either have a short bypassing the fuel pump relay, or a deliberate bypass, custom wired bypass of the FP relay!!!!

Going from the front of the jeep to the back, Relay #2 is the FP relay:

http://www.lunghd.com/Downloads_and_Links/Jeep_Renix_Fuel_Injection_manual.pdf

See page 69.

Yes ... agreed ... could be a short in the wiring under the base of what should be the fuel-pump relay ... I had a similar very interesting (at least I thought so) situation with the wiring under the aux-fan relay base that I had reported back on during April 2010 .... here's the link to the aux-fan relay situation:
http://www.naxja.org/forum/showthread.php?t=1020865

So ... I'll put it on the to-do list to look at the wiring under the base of the fuel-pump relay (regardless whether or not the recent failure-to-start problem occurs again).

Been a while since I reported-back on this ... here goes:

Without doubt, the fuel-pump is not pushing any gasoline int the fuel filter
- so,
I need to buy another pump.

What I remember from reading other posts over the years:
there have been some posts that say to stay away from the Airtex pumps.

Which leaves these choices via RockAuto (for '87 XJ 4.0L):
Omix-Ada #177090, $110, 3-yr warranty;
Bosch turbine #69302, $81, 1-yr warranty;
Carter #P74057 with Walbro OE pump, $72, 1-yr warranty;
Carter #P74155 with Bosch OE pump, $74, 1-yr warranty.

Are there any recommendations for a reliable fuel pump for a Renix XJ ?

This '87 XJ has the 13.5 gallon tank.

I am looking at warranty periods since the current failed pump was installed only ~ 27 months ago along with a new filter shortly after (currently with ~ 20,000 miles on it) ... yes, the failed pump is not under warranty ... was locally bought by a local repair shop and no on remembers what the brand was.

Regarding how the fuel pump is being powered without going thru the passenger-side #2 relay under the hood:
turns out I've been driving this '87 XJ for the past ~ 200K miles where someone prior had run a speaker-wire from the 7.5 Amp "gauges" fuse from the drivers-side foot-well fuse-bank,
then under the rugs to under the rear-seat and twist-tied (not even crimp-connected) that speaker-wire line into the red line (that then feeds into the OE weather-pak connection that then feeds into the fuel pump).

When I pull the speaker-wire out from being jammed-into between the ATC blade-fuse and the fuse receptacle, there is no power to the pump (similar to a "kill switch" for the pump).

Yes, I am going to correct that power-feed into the pump after the pump is replaced.

Have you tried running a 14 ga wire set from the battery to the fuel pump directly?

I would try that first, and test the fuel pressure. If it runs but no, or too little pressure, then drop the tank and see if it is a hose inside the tank problem, before you buy anything.

Before the test that showed no flow from the pump,
I had cut-out the twisted-together wire connections along the speaker-wire
and replaced with a single tube-connector crimp covered with shrink-tubing
- the speaker-wire looks like it nets to at least 14-ga diameter.

I then charged-up the battery 100% followed by testing with a multi-meter:
there was 12.5 volts at the battery terminals;
there was 12.0 volts at the rear under-the-vehicle OE weather-pak connector for the fuel pump.

The pump was humming and whirring loudly
during the flow-test that showed absolutely no gasoline flow
(zero flow ... not 1 drop) from the pump
via dis-connecting the pump output-hose that goes into the fuel filter.

The reason that I am suspecting pump failure
is when the ignition switch is 1st turned-on the pump sounds very weak
and then over ~ 30 seconds the humming and whirring sound gradually gets louder.

And when I think about how the original problem temporarily corrected itself
(pump noise changed from a humming-whirring to a tick-tick-tick ... see my 1st 05/28/2011 post)
I am currently suspecting the pump's internal impeller either has come loose or is blocked
rather than suspecting the inside-the-tank connector-hose has come loose.

Note: I had changed the fuel-filter ~ 20,000 miles ago ... ~ 2 months after this pump was installed.

Sounds more likethe hose inside the tank came loose, and it is just circulating gas inside the tank. You need to pull the pump assy anyway. Why do it first, before buying a pump you may not need?

I think I will go with the Omix-Ada #1770909 ... regardless a bit more expensive.

I did some brief searching (all that I have time for right now)
- what I found was interesting:
some repeating stories from different people regarding 2-year-old replacement fuel pumps failing (which is near-exact where this '87 XJ is right now):

http://www.naxja.org/forum/showthread.php?t=1047880&highlight=fuel+pump
11/2010 posts:
"... Maybe yes, maybe no. 87-93 (Renix and HO) all can use a Bosch 69302 pump ..."
"... Funny you mention that bosch 69302. The one I am about to take out is the second 69302 since 2006 that went bad. The original pump lasts 20 years and I cant make these aftermarkets last 2. ..."

http://www.naxja.org/forum/showthread.php?t=977956&highlight=fuel+pump
12/2008 posts:
"... So my 2 year old Bosch pump died...."
"... The Bosch p/n 69302 pump that I replaced in my post #7 with another 69302 is dying on me just like the last one did.
Two years on the first replacement Bosch 69302, and one year and one month lifespan on this one. ..."

I specifically seek out Bosch pumps. They are the best in the business.

Not sure, but I thought Omix-ada was an Airtex pump?

I wonder if a lack of a ballast resistor, or poor wire connections in the jeep, is causing the pump to get the wrong voltage, and damaging the pumps?

Ecomike said:

Not sure, but I thought Omix-ada was an Airtex pump?

I wonder if a lack of a ballast resistor, or poor wire connections in the jeep, is causing the pump to get the wrong voltage, and damaging the pumps?

Click to expand...

the ballast resistor was added to quiet the pump due to soccer moms complaining of the noise. The pump will run at 14V and be quite happy about it.

Poor wiring would cause the pump to not work, but should not damage it. A fuel pump is a pretty stout/simple electric piece.

I would pull the pump, see if it really is bad or if it's just sucking air from a failed pickup tube. If it is really bad, then replace te internal pump with a piece of hose and mount a new pump on the frame rail protected by the trans cross member. You can use the ford e2000 pump, or the aeromotive pump I used for my fuel cell. At least then it's easily serviced, and iut's also behind the fuel filter, so it's less likely to eat crap and die. Just make sure you change the filter regularly, as a restriction on the suction side of the pump will more easily damage it than a restriction on the pressure side.

This:
http://www.summitracing.com/parts/AEI-11109/

is the pump I've been using with my stock Renix fuel system. no problems in 2 years, but it's just a trail rig, maybe 50 hours of actual run time? Anyway it's properly sized to do the job and doesn't run excessive pressures before the regulator. It is not quiet, so if you are averse to the pump hum don't use it.

re: immediate-prior thought
"I wonder if a lack of a ballast resistor ... is causing the pump to get the wrong voltage, and damaging the pumps? "
- I was thinking exactly the same thing while driving home last night in the '94 Bonneville.

That is:
especially since the '87 XJs do not have an OE ballast.

Which might be another reason to go with Omix-Ada ... since Omix-Ada may take that '87XJ no-ballast OE configuration into account ... whereas the other pump manufacturers may not.

I was assuming the new, cheapo-china pumps may be more sensitive to operating voltage, and spikes.

But I have read many posts here, where the hoses came loose in the fuel tank, and lost pressure, but the pump was still OK!

Also, FWIW, these pumps depend on the gas in the tank to cool the pumps, so running the tanks empty all the time in peak summer heat, heavy traffic, may shorten the life for newer marginal pump designs. Add a little overvoltage (perhaps?)....

I think the ballast resistors were added so that when the engine was cranking, and battery voltage drops to 10 volts, the fuel pump would get full power (10 V), then once running they wanted to hold the fuel pump voltage lower (10-12V?) versus 14.5 volts.

I wonder if we have fuel pump OEM engineers running loose here?

Is the Renix pump a diaphragm or centrifugal turbine design? Anybody ever dissected one?

Ecomike said:

I was assuming the new, cheapo-china pumps may be more sensitive to operating voltage, and spikes.

But I have read many posts here, where the hoses came loose in the fuel tank, and lost pressure, but the pump was still OK!

Also, FWIW, these pumps depend on the gas in the tank to cool the pumps, so running the tanks empty all the time in peak summer heat, heavy traffic, may shorten the life for newer marginal pump designs. Add a little overvoltage (perhaps?)....

I think the ballast resistors were added so that when the engine was cranking, and battery voltage drops to 10 volts, the fuel pump would get full power (10 V), then once running they wanted to hold the fuel pump voltage lower (10-12V?) versus 14.5 volts.

I wonder if we have fuel pump OEM engineers running loose here?

Is the Renix pump a diaphragm or centrifugal turbine design? Anybody ever dissected one?

Click to expand...

x2 on the rubber hose in the tank coming off. My 89 did that at 300,000mi.

So I took out fuel pump assy. and saw rubber fuel line was half way off and put it back right.

Then after installing it back it didn't run. Seems the connectors were jacked up a little, fixed that and my stock pump is still pumping at 397,000mi.


I got a back pump from the JY out of an old 88 xj, I trust the old OEM Bosch over any new stuff.:gee:

OK:
just called up RockAuto Customer Service ... as good luck would have it, the rep who talked to me has a 99 'XJ and he recently had to replace the fuel pump on that vehicle ... which he used the entire set-up SPECTRA PREMIUM Part # SP7121M.

Regardless ... here is the focus:
I asked him 2 questions:
#1:
can I return to RockAuto an un-used new fuel pump (should it be the case that I order a new pump from RockAuto and then return it due to the current problem actually being a loose hose);
#2:
which fuel pump brands on the RockAuto site are more reliable than others (in terms of what he knows regarding customer returns due to failed pumps).

To question #1, his answer was:
you have 30 days to return the unused new pump to RockAuto where you pay for the return ship but there is no re-stock penalty fee within those 30 days;

To question #2, his answer was:
RockAuto closely reviews returns due to product failure and when the return % goes above 2% to 3% of unit sales for the product, then RockAuto removes the product from it's site ... therefore: all the fuel pumps currently listed on RockAuto are currently seen (by RockAuto mgmt) as being reliable.

The reason that I am buying the pump now (whichever brand ... now I am thinking maybe Denso instead of Omix-Ada) is because as is my normal mode of operation I need to fit doing 10 pounds of stuff into the weekly 7 pound bucket (which is why I couldn't get to doing the pump flow test until this past weekend) ... and, I lined-up a local repair place for sometime next week to do the labor on this job.

The additional reason that I am currently believing that the pump has failed is 2-fold (as I had written yesterday):

- currently when I turn the ignition-switch on the pump starts out sounding very week and takes ~ 30 seconds to start making the louder buzzing-whirring noise (and yet, pumps no gasoline);

- when the problem started on 05/28/2011, this '87 XJ would not start while the pump was making the buzzing-whirring noise ... and then as the battery was about to go down to totally-drained then the pump "all of a sudden" kicked-in to making a tick-tick-tick noise and with the last battery energy it slowly cranked-over and immediately started and I then drove the ~ 37 miles home at mostly hi-way speeds without any problem whatsoever
(which I just can not see as being a loose hose, given the question as to what would have caused the hose to tighten-up and why did I have no problem driving home the 37 miles at ~ 60 MPH).