PCweber

I have a 92 4.0L with the common rough cold start issue that clears up when started. I ahve searched and read many diff. posts about it and most have a common theme of "yep, mine does it too, live with it". With that, is there anything that seems to work to help the rough start be as good as possible? I am noticing as things are getting colder this fall the start is getting rougher. As anf FYI, I havee stated cycling the key twice before starting. Anymore than 2 key cycles and the fuel pump will not run when the key is turned on.

Dogberri

when you say "rough start" do you mean it turns over many time before firing or it idles rough after its started?

trans_am7935

use thinner oil

lurk520

Mine does it too...by rough start I mean it takes 2-3 seconds to kick over but always starts on the first crank, and it sounds like a janky start. But once it's been started, it will fire up nice and smooth until it sits for more than a few a hours, regardless of the temperature. So my guess would be the fuel pump is a little weak. I Had a similar situation on a previous vehicle, and it turned out to be the fuel pump, except it wouldn't start on the first crank in this previous situation, but this is a different kind of vehicle we are talking about. My plan is to replace the fuel pump in the near future since my fuel gauge is F*&^ed anyway, if that doesn't work than o well, process of elimination..... first I thought it could be the fuel filter, but I already replaced that...step one of the process....

PCweber

Like lurk520 said. I searched and found 10-12 posts and many replies in the form of " mine does too, I just live with it". It is not a cranking/ starter issue. Seems like fuel system has gotten air in it. Some people say the fuel pump check valve has gone bad and is leaking down. Mine alwys starts but coughs a bit then clears right up. I was just wondering if someone has found a best practice that works for them. I ddi read to cycle the key a few times and do that but it still is a bit rough. May ned to get a wiring diagram and put a push button switch in to allow to push teh button and run the fuel pump constant to "prime" the fuel system and get all air out maybe.

dukie564

I totally agree with him. Run a 0w-30 or a 5w-30 to improve your cold starting. (the #w is the cold weight number - the lower the number the more viscosity it has when cold).

*Note* do NOT change to a SAE 20 oil. stay with SAE 30 for our engines.

djb383

It's exactly the opposite, the lower the number, the LOWER the viscosity (thinner) when cold.

dukie564

you are correct...my bad

djb383

Properly tuned/maintained, computer controlled EFI engines should run/start quickly & smooth, immediately, cold/hot/or anywhere in between.

lurk520

A few days ago I put my jeep in the shop because it randomly stalled on me while slowing down for a school zone, and then it wouldn't start again for 15 minutes. So the shop has tested everything, and they are saying they can find absolutely nothing wrong with it. But any way they are claiming my rough start when cold issue is due to dirty fuel injectors, so they are being cleaned. So I will let you guys know if it actually works when I get home....

PCweber

I fixed mine. It would lose fuel pressure instantly on the fuel rail. It is a common issue that a check valve in the pump goes out. So, instead of $240 for fuel pump I put a temporary push button switch just under dash that applies 12V to the baallast resiston on the inner fender by the brake booster. (fuel pump power). I press it for 2-3 seconds before cranking cold, starts instant.

lurk520

did this ever cause you to stall randomly?

p.s. the shop also said the fuel pump is very expensive (over 200$) but....I've found it at two different places for around 100$

PCweber

never, other than long crank on start I dont have an issue.

PCweber

get a momentart contact sitch and some wire. Hook 1 side of the switch to power in fuse box, other side to either side of the ballast resistor on the driver's side fender well. Push the button with the engine off and you should hear the fuel pump hum. Go for a drive. THat thing starts to die hit that button. If it does not help that tells you it is not the fuel pump. (assumignt he fuel pump is not intermitant. I would let it die some times too and hit that button to see if it hums right away) you also could go to Harbor Freight and get a fuel press. gauge. Hook it up and leave it on while you drive. It starts to die puull over and see what fuel pressure is up to. Keep in mind mine (and tons of these XJ's based on how many have long crank issue.) when the engine is off the fuel pressure drops to zero very fast.

PCweber

Fixed! It was the temp sensor that goes in the thermostat housing in front of engine. I had picked up a non running Cherokee and tried sensors 1 at a time, then took the truck to the U-Pull It. Got a set of 4 aluminum wheels and tires and a few other parts and got $50 more for the thing than I spent!