Fuel delivery/circut questions...HELP!!!

Okay, using the search I did on this topic I was able to diagnose my no start condition as a faulty resistor. When I bypass this resistor the jeep starts and runs fine. My questions is, I am currently at work and don't have another way home! How long can I run with the resistor bypassed w/o frying my pump or other components? THanks, CHris.

My 87 never had one, I think it's more for noise than anything else.

Hey, thanks for the fast response, at least now I can go home! What a day-mare. The thing would run with the key in the Start position but not in run. I'd turn it to start, bump it over w/o letting it start, turn it back to run, check the schroder (sp?) valve and it would spit just a drop of fuel out. If I'd let it start then die, there'd be no fuel at the rail. The jumper seems to have fixed it though. Also, while I did the search I noticed that you seemed to know quite a bit about this system. I have had a problem since I purchased this jeep that I would call a "slow" start. THe motor must turn over 5,6 7... times before starting. It seems to have spark from the moment I turn the key. I figured it's prolly a fuel preasure regulator not holding the preasure in the system, but letting it leak by back into the tank. WHat are your thoughts? Thanks again for your help! CHris.

cnflxj said:

Hey, thanks for the fast response, at least now I can go home! What a day-mare. The thing would run with the key in the Start position but not in run. I'd turn it to start, bump it over w/o letting it start, turn it back to run, check the schroder (sp?) valve and it would spit just a drop of fuel out. If I'd let it start then die, there'd be no fuel at the rail. The jumper seems to have fixed it though. Also, while I did the search I noticed that you seemed to know quite a bit about this system. I have had a problem since I purchased this jeep that I would call a "slow" start. THe motor must turn over 5,6 7... times before starting. It seems to have spark from the moment I turn the key. I figured it's prolly a fuel preasure regulator not holding the preasure in the system, but letting it leak by back into the tank. WHat are your thoughts? Thanks again for your help! CHris.

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It could be the regulator, the pump or a leaking injector, my guess would be a bad pump.
Your problem now may still be a bad pump, jumping the resistor only sends more power to it.

The 4.0L takes more "turn overs" to start than most EFI engines. This is due to how the ECM initialy determines where the crank is; don't think it's "6/7" times, though.
I've replaced my 4.0 with a Cheby, so my memory has faded with regard to how many turn-overs before starting. There are specs on the leak down rate of the fuel rail pressure after shut down. If the check valve in the fuel pump is not holding pressure, the symptom will be too many cranks before starting; the fuel rail leak down test will confirm this.

If it's the ballast resistor, it was put in the 1987 as a "voluntary recall" and added to the 88-up for NVH (Noise, Vibration, Harmonics) issues.

The ballast resistor is there as a current-limited device for the fuel pump, to keep the pump's operating noise down. I've taken it out on my 87 and my 88 because I actually like a little noise - reminds me that everything's running. I also tend to base a lot of my troubleshooting on noises - so it's additional input for me.

The ballast resistors on my two 89's are still in place, since my wife regularly drives them. She's a little more sensitive to noises while driving than I am (which is really odd, since I hear better than she does...)

You can theoretically have no ballast resistor in there indefinitely - just put a bit of wire in and leave it at that. Make sure that the terminals can't hit sheetmetal, you don't want to short out the circuit!

The ballast in my 87 wasn't there when I got it (circa 1996) and I haven't had any trouble. The ballast in my 88 came out about five years ago.

As far as the "long crank," that's a known quirk of RENIX. The ECM looks for two things before it sends out ignition and FI signals - 300rpm crankshaft speed, and a valid SYNC pulse from the distributor. It will start without the SYNC pulse if it has to - but it prefers to have the signal. Just get a high-torque starter next time, and you're good - that's what I do.

5-90

The ballast resistor was a "cure" for noise, as 5-90 said. I'm using the stock XJ pump to feed my "Cheby" multi-port FI--and I'm not using the resistor. I've run the engine many hours that way without a problem.