Hans4real

Quick question. Never replaced or cleaned the injectors in my '98 4.0. Last week it started to run poorly at start up but only for a few seconds. Once I drove 20 feet or so or put some RPM to it she cleared right up and ran and idled like a champ. If I shut it down and then start it right back up, no issues. If I let it sit for 30 seconds or so, then it goes through the whole running like crap until I rev it or drive a few feet. Is it leaking injector(s)?

Stabsthedrama

I would say it's easy enough to pull the fuel rail off and just put a sheet of cardboard down under the line of injectors, prime the fuel pump and see if any of them leak (don't crank it over, just put it to ON position) - but A) it's not a 100% fool proof check, and B) at that point you might as well just swap out the injectors, since 1/3 of the work is already done taking out the injectors anyway. A refurbed set of Bosch type III 4 port injectors will only run you 60-100$ anyway. The only thing you need to do after taking the rail off is removing the fuel lines (and replacing the o-rings and spacers or clips or whatever on the send and return), swapping out the injectors, which will come with new o-rings if refurbed, and then throwing an o-ring in the FPR (same o-ring as the injectors each have, can be found in the Dorman section of any auto store) - and then re-assembled. Sounds like a lot, but IMO if you're going to be pulling the fuel rail anyway, you might as well just swap out the injectors for upgraded ones anyway. You can also clean out the injector ports.

Disclaimer - this comment does NOT mean that this is even your problem, just advice if injectors are what you decide is the problem or what you want to tackle first.

I would maybe look into seeing if your MAP tube is ok, and possibly even cleaning out the IAC.

Checking fuel pressure should probably be your first step if you don't want to get too deep into it, because you can see if the pressure drops off slowly or quickly while injectors are still in and you turn the truck off, which can tell you if injectors are leaking (but again may be hard to interpret for sure.)

Hans4real

Awesome information and thank you. To make sure I check the correct tube, where exactly is the MAP tube and what does it go into. And do you have a links to the seller of the Bosch injector parts?

Fred/N0AZZ

Sounds like a good time to upgrade to a 4 hole injector that has been cleaned and rebuilt a cheap upgrade from "programo" here on the forum.


Mine looked like brand new and made a noticeable difference to my engine.

Stabsthedrama

MAP sensor - http://imgur.com/oew5mQR

https://i.imgur.com/JiL9wm5.jpg

The line will be part larger rubber hose, part hard line that goes into your TB. Just check the line for any visible cracks. With the engine running, you can take it off from the connection shown in that picture - it will either completely shut the engine down (it does on mine) or run even worse. I would guess that if it doesn't change at all, you may have a vacuum leak or the sensor itself is bad, you can google how to check the sensor. It's a long shot, but just make sure to check the hose.

It's also good to know this since it's very easy to accidently snap that hard MAP tube when doing the injectors/removing the fuel rail (ask me how I know) - you are supposed to replace it with hard line since it cannot have low spots in the line (moisture will gather) but if you do a straight enough line of rubber vacuum hose with no low spots/sagging spots I'm sure it's fine (it's what I changed mine out for) - actually the plastic nipple on my TB grommet also snapped so I bored it out a bit and shoved a plastic vacuum line connector into it and the rubber vacuum hose right onto that, and just a rubber hose all the way up to the MAP sensor.

Hans4real

I'm on it tomorrow to check the lines for cracks. I have another complete throttle body with all the connections for a complete swap without removing any sensors. Swapped it out and no difference. Thanks for the replies. Stay tuned if you would and add input whenever.

Firehawk068

On the '98 the MAP sensor is mounted right next to the throttle body, with just a small rubber elbow connecting it , directly underneath it.

DFlintstone

96 or so the MAP moved from the firewall to right on the TB. No more brittle little tube to break. This one idem alone, is the one, sole improvement over the pre 91 Renix Jeeps. (my new map line is solid molybdenum).

I might go ahead and check the fuel pressure, and for codes.

Stabsthedrama

Huh.... learned something new today. I had a 96 but never had to deal with the MAP or take notice of it. I wouldn't even say it's all that much of an improvement, I mean maybe over stock - but for like $2 you can just replace the hose once in a lifetime on a Renix.