giacomo.m

Hi all,
1990 XJ 4.0L automatic to which I replaced the injectors with Bosch 280155746
during disassembly I broke the vacuum tube that goes from the throttle body to the map sensor and at engine start I now have rough idle-sputtering / misfire
before replacing the injectors the engine ran well with low idle and high fuel consumption
is it just a problem with the vacuum hoses or could there be something else ?
thank you

Giacomo

Roler

You'd have to repair that vacuum
other than that, check the work that has been done again. Check the new injectors are seated properly and ensure you hooked the connectors back up correctly.

lawsoncl

Yeah, it's going to run like crap until you fix that line to the map sensor. It's easy to get the injector plugs swapped too, but you can compare wire colors to the FSM to double-check them.

ajpulley

First, use punctuation so we don't have to decipher a paragraph.

Second, replace the plastic tube with a new hard plastic tube. Or, use 3/16-inch brake line bent to match the original shape if you can't find the original. Do not use vacuum hose alone as it is too pliable for the MAP sensor to give the ECU precise voltages. The broken tube throws off what the ECU sees as manifold vacuum. The ECU needs this input while in open-loop and closed-loop operation. The broken tube also creates a vacuum leak on the intake manifold side of the throttle plate.

cruiser54

CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY TO MAP SENSOR HOSE FIX

JANUARY 23, 2016 CRUISER54 43 COMMENTS EDITThe Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase.

The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause major starting and driveability issues.

There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket ( Napa FPG 60742 ), a vacuum fitting (Napa 05703-B102), two vacuum elbows (Napa CRB2670), and a length of new plastic piping (Napa CRB2672).



Remove the throttle body and take it to the workbench.

Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body where the old fitting was plugged in. Don’t go too deep. These are pipe threads.

Flush the hole with carb cleaner and inspect for any left over cuttings.
This is an excellent time to do a complete throttle body and IAC cleaning. See Tip 11.
Take the vacuum fitting (05703-B102 ) and apply a LITTLE bit of thread sealer on the threads only. I prefer Permatex #2 but almost anything is fine.

.

Carefully screw the fitting in until snug.

Install one of the vacuum elbows on the MAP sensor so it points toward the throttle body, and the other vacuum elbow on your new throttle body fitting so it points up to the MAP sensor.
Cut a length of the new plastic tubing (approximately 13 inches) to fit between the vacuum elbows and install it making sure there is enough slack for some engine movement. Route it according to the photo. We don’t want any rubbing or chafing with engine movement. Not a bad idea to use some contact cement or Gasga-Cinch sparingly on the tubing to elbow connectors.

cruiser54

giacomo.m

Thank you cruiser54
but the top hole must be open or closed ?

Giacomo

cruiser54

The top isn't a hole. It's just a deal to hold the fitting on better.
Off to work for me. What time is it in Italy? It's 7 am here.

giacomo.m

Hi
at this time in Italy it is 21:15

Giacomo

giacomo.m

Hi,

injectors replaced, but now the engine idle has gone to 800/900 rpm,
is this normal or do you need to make some adjustments ?
thank you

Giacomo

cruiser54

Drives okay?
Go drive it. Make sure you got that line to MAP sensor perfect.
Make sure your intake manifold bolts are tight.

giacomo.m

Drive ok
the vacuum line to MAP sensor is not perfect, I still have to make the change you recommend,and I have to check the intake manifold bolts......
thank you

Giacomo

cruiser54

That hose/pipe can have NO LEAKS. If it does leak, the MAP sensor thinks the engine is under a load and the ECU adds gas.
You don't have to do the complete fix in my Tips. Just get something on there that doesn't leak.

giacomo.m

Thank you
but I want to do a correct and final job and in this regard I was wondering if you can fit a barbed 90 degree vacuum fitting,when mounted on the throttle body can it be operated with the wrench ?

Giacomo

cruiser54

I'm not sure. the throttle body has to be removed anyway to tap the hole for the fitting.