Rough Starting 90 No matter when

1990 4.0L AW4. Ok well I understand about the Renix thing so I realize it's not going to start right away, but this is rediculous. It doesnt take enough time to hurt the starter or anything but it probably takes 6-8 seconds. When I go to crank it no matter if it has been running a while or not(although it is easier if it has been) it will skip past and not fire. You can hear it trying and it will almost catch. The problem is whenever I take it to mechanics they don't hold it long enough and it doesnt start so then they have to recrank it. Im trying to figure out what the case is here. I have a new cap and rotor, but old wires and plugs. Would wires or plugs be causing this or would it be something else?

I would lay hands on a fuel pressure guage. Sounds like the fuel pump isn't getting up to pressure for a while. It could also be a fuel pressure regulator.

Could also be the battery or battery cables. I replaced the cables in my '90 with a heavy duty 2/0 set, and it make the starter turn significantly faster. Try jump starting with another vehicle and see if it starts any quicker.

When I jump start it, it does turn much quicker. Where did you get the heavy duty cables? I will look into that fuel pressure gauge too, thanks.

When you start it, do you wait with the key in the ON or RUN position until the fuel pump stops running before you turn the key to START? The fuel pump will run until the fuel rail has full pressure, then shut off. I have always waited for the fuel pump to stop before cranking. If you're not doing that, try it and see if it helps.

jeepguy1990 said:

When I jump start it, it does turn much quicker. Where did you get the heavy duty cables? I will look into that fuel pressure gauge too, thanks.

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I made them myself. Actually, I've got an extra set if you're interested.

Just to show how much bigger the 2/0 is:

The top cable was my stock battery cable, bottom is 2/0. :shocked:

all of the renix jeeps have a longer crank time than the newer jeeps. but back in 90 there were some fuel pump issues for bleeding back after sitting for a while. if the fuel pump has never been replaced, it could have that problem. you do need to test the fuel pressure to confirm or rule out this.

jneary said:

all of the renix jeeps have a longer crank time than the newer jeeps. but back in 90 there were some fuel pump issues for bleeding back after sitting for a while. if the fuel pump has never been replaced, it could have that problem. you do need to test the fuel pressure to confirm or rule out this.

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Yes, but it should be around 4-5 seconds, as oppsed to <2 seconds for newer engines. 6-8 seconds is too long.

ZmOz said:

Yes, but it should be around 4-5 seconds, as oppsed to <2 seconds for newer engines. 6-8 seconds is too long.

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where are the specs for crank time on the renix system.they all have a longer crank time. that was a characteristic or the system. i have been working on jeeps since 1988. i have seen the customer's complaints for this in the beginning, and everything jeep (chrysler now) told us to do, didnt improve much if at all. it is what it is. i have an 89 myself. i know what to expect and it doesnt bother me.

jneary said:

where are the specs for crank time on the renix system.they all have a longer crank time. that was a characteristic or the system. i have been working on jeeps since 1988. i have seen the customer's complaints for this in the beginning, and everything jeep (chrysler now) told us to do, didnt improve much if at all. it is what it is. i have an 89 myself. i know what to expect and it doesnt bother me.

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I have no idea what the actual spec is, but I know no jeep ever left the factory with an 8 second crank time. That is ridiculous. My '90 did take a long time to start, but it was only around 5 seconds. It was about 3-4 seconds after I put in new battery cables. It's not really a matter of time, it's a matter of revolutions. The Renix system needs something like 5 complete revolutions before it will start. If you can upgrade the battery cables, then the starter turns faster and it of course starts faster. From the factory, the cables are barely adequate, but they do the job. 14 years later, they're corroded, the battery isn't brand new, the starter is a little worn, etc and a cable upgrade is in order. Same goes for the fuel pressure, as it gets older the pump and pressure regulator wear out, and it takes longer to start. Fix those things, and it will start like new again.

so what if take 5 or 8 seconds. that is a 3 second difference. why waste the money to change these things for 3 more seconds. who is in that much of a hurry? leave the house 3 seconds sooner.

ZmOz said:

I made them myself. Actually, I've got an extra set if you're interested.

Just to show how much bigger the 2/0 is:

The top cable was my stock battery cable, bottom is 2/0. :shocked:

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Im real interested in them. Can you shoot me a price? Either PM or respond here. Thanks. I will try the fuel pump warmup thing too Eagle thanks for the tip.

jneary said:

so what if take 5 or 8 seconds. that is a 3 second difference. why waste the money to change these things for 3 more seconds. who is in that much of a hurry? leave the house 3 seconds sooner.

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Maybe you don't care, but most people do. Obviously this guy does, and so did I. If you don't want to fix your problem, that's fine, but there's nothing wrong with someone wanting a quicker crank time. Your starter and battery will both last longer anyway...

Check your PMs jeepguy.

I have a '90 and it alway started rough and took a while. I foung a like new starter at a salvage, and since mine was always noisy, I popped it in. Presto! It started about twice as fast now, and queiter and smoother. Just my experience.

Thats the other thing my starter is real noisy too. Im running an OReilly rebuilt though so that may have something to do with it.

ZmOz said:

Yes, but it should be around 4-5 seconds, as oppsed to <2 seconds for newer engines. 6-8 seconds is too long.

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4 - 5 seconds? My Renix starts usually in less than 2 seconds of crank time. On cold mornings it may take 3 or 4, but it's never longer than that. Even the ~2 seconds bothers me, especially when I look at newer vehicals and they start instantly.


Is the fuel pump original? Might want to go in for that recall or whatever it was. I was looking over the warrenty information book for my '90, and it has the fuel pump shown replaced at ~12k miles. The second one made it to ~168k miles. Go with the OME pump, I wish I did.

If none of the ignition stuff helps, it might be time to do a compression test. It is a 14 year-old vehicle after all; it may just be your rings are worn to the point that they're not holding enough compression until they're really oiled up.

By the way, my '90 cranks in about two seconds: rahr-rahr-rahr-rahr-ruuummmmm.... I don't know if each sound peak it makes while starting corresponds to a complete engine revolution or only 180.° I've also found that having the TPS properly adjusted and the PCV system functioning properly helps a lot.

:revolver

I don't think compression would cause that, and if it were a problem, it would just run poorly but start in the same time.

Here are some things based on the improvements seen after various rework over time on my 89:

Grounding is poor! This will affect sensor voltages to the computer. remove, clean, and use ox-gard on the block, battery, starter relay, and firewall connections at least. I'd also use Deoxit-D5 on all of the sensor harness connectors.

Bigger cables are good. The RENIX needs 300 rpm before it will begin operating per its manual. This means good power to a good starter and a good starter.

Once it gets good signal from the CPS, it will begin firing with cylinder 1 (or 6). You can put a noid light on the HV coil wire, have someone crank (or use a remote) and see if you start getting spark long before it actually turns over. If it does, then the computer is happy and starter, CPS, distributor, etc are OK. If not, it's not happy and it's probably electrical or sensor related.

If the computer is happy and firing, check fuel pressure. Also check the B+ relay. It's supposed to keep power on after turning the engine off for a few seconds to allow the idle stepper motor to assume the 'starting' position. Not sure if that's more open or closed than running, but you could try removing a vacuum hose, say to the CCV system, and see if that helps. Perhaps it's trying to adjust it and that takes a while because it thinks it should be ready already. The computer also energizes the EGR solenoid during start, so that may be stuck. you don't mention if it's totally dead or tries to start during the extended time...

If it's looking like a fuel/air related problem, try different pedal positions to see if that changes things. Part open should richen it, and floored will shut off the injectors during cranking (it is programmed to do that so you can clear a flooded condition).

If that doesn't help, report back on more detail, like 'does it start faster after JUST having been shut off?", "does it stumble?", "what did the above tests result in?", etc.

Good luck.