Any problems with Bosch..

...spark plugs or wires on the 4.0. I just replaced my old ones with Bosch, and now the truck seems to be running rough?

Could this be related?

Make sure you got on the wires on in the correct order.

A lot of people would say stick to Champion Plugs. I know when I put new plugs in after I bought it. Ran like new.









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'91 XJ, Laredo, stock.

check to see that the plugs are gapped correctly

i always use bosch plugs. never had a problem. never used their wire though.

I have used a blue bazillion Bosch plugs in Volkswagens..only seen a few bad ones...You could have the gap too tight...or maybe cracked a insulator when you installed 'em....

You didn't say which version plug...conventional, dual or quad electrode. IMHO stick with the conventional plugs...the multi electrode plugs shroud themselves...there are two brands I personally recommend...NGK and Motorcraft..whichever brand is available at the time, they are just as good.

.02
Bosch plugs have their place. Bosch "super" plugs suck. I first experienced this when I put them in a 350sb and couldnt figure out what was making it run bad. Almost took the engine apart convinced something was seriously wrong. Just experienced the curse of bosch supers again when I almost had to reposses a car that a customer thought was bad because they took it to firestone for a tune up. I told my customer about my experience with bosch supers and replaced them with delco's(gm car) and the car ran much better. He took the plugs back to firestone and complained until he got his $126(thats how much they charged him to install 6 plugs in a fwd v6 regal.) returned.
I do enjoy the performance of bosch platinums. Cant go wrong with the platinums.

In a word, yes. Do not use them in anything as far as i am concerned. Have been the subject of many auto manfacturers TSBs for misfiring issues. Modified programs have been needed in many German vehicles to combat ck engine lights due to misfiring codes being set. Especially do not use platinum plugs in anything not designed for them. The only benefit to platinum is that it does not wear as fast- they do not otherwise perform as well as standard plugs. Darned 'ole cheapo Champions work great in these 4.0s. I am considering NGK irridium (sp) plugs maybe next time maybe however just to see.

Had some serious cross-fire issues in a, new to me 88 4.0. Pulled the Bosch multi electrode plugs, replaced with stock Champions and 60-70% of the missfire disappeared. Noticed a long time ago, the plugs the vehicle was set up for, in the original design, generally work best, with computer controlled vehicles.
Also noticed the inside plugs (middle cylinders) were burning leaner than the ends. After changing to stock plugs, the plugs mostly, burned a light grey and equally. Thought it was a fuel issue, now it seems it was a resistance issue, with the Bosch plugs.
I´ve used Bosch and NGK in vehicles designed to run these plugs, last well, work well. Believe the design parameters of these plugs, is figured into the ECM, on vehicles designed to run these plugs. Same with the Jeep and Champions.

heat range is for the plugs is the big thing to watch for.

Cottontail said:

...spark plugs or wires on the 4.0. I just replaced my old ones with Bosch, and now the truck seems to be running rough?

Could this be related?

Click to expand...

I used champion and bosch plugs in my 94 and never noticed a lick of difference.

I would make sure the order is correct (as said) and also make sure to not get any dirt or grim in the plug holes. That makes a big difference and can ruin a motor.

Bosch Single or Multi Electrode Plugs

I had perfect behaviour and long life from the single-electrode Bosch Platinum plugs in my 1990 4.0 I have read a lot of concerns over the multi-electrode types- different animal from the single electrode (conventional) plugs with a platinum tip. Currently running NGK standard plugs, and I can't tell the difference: both perform beautifully in mine. 4xBob

Judd W. VA said:

In a word, yes. Do not use them in anything as far as i am concerned. Have been the subject of many auto manfacturers TSBs for misfiring issues. Modified programs have been needed in many German vehicles to combat ck engine lights due to misfiring codes being set. Especially do not use platinum plugs in anything not designed for them. The only benefit to platinum is that it does not wear as fast- they do not otherwise perform as well as standard plugs. Darned 'ole cheapo Champions work great in these 4.0s. I am considering NGK irridium (sp) plugs maybe next time maybe however just to see.

Click to expand...

This advice is right on the money. Check the TSBs. The platinum plugs can cause misfire and check engine lights in some vehicles. It messes up the computer control in some vehicles. I experienced it with my van (ended up changing plugs in the middle of vacation, no fun in a front wheel drive van). Rule of thumb. If it didn't come with platinums oem don't use them.