finished HG job... now a miss at 2k rpm: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Dec. 26, 2011 2:08 p.m. donalson SuperDork

I just finished getting everything back together from replacing my HG on my volvo '91 945ti

now i'm getting a nasty miss right around 2k... feels like i'm bouncing off a rev limiter... if I give it a little more throttle it'll get past that and runs just fine at higher RPM or if you can manage to stay under the 2k

I skimmed the head, replaced the broken non OEM Oil separator box with an OEM replaced the exhaust manifold studs (had a few bolts instead of studs so replaced)... new bosch platinum spark plugs, the timing belt and tensioner was replaced about a while back

so anyway here is a quick vid... http://youtu.be/Y9CfXsF8xD8

anyone have any thoughts or ideas of what/where to look at?

thanks guys mark
Dec. 26, 2011 2:14 p.m. Curmudgeon SuperDork

Sorry, I know nothing about those cars.
Dec. 26, 2011 2:27 p.m. 93gsxturbo HalfDork

Are Platinums suggested? Most turbo cars run like crap with those. Toss a set of standard NGK coppers in there and see what it does.
Dec. 26, 2011 2:28 p.m. 93gsxturbo HalfDork

Otherwise, is everything hooked up? No boost leaks?
Dec. 26, 2011 2:40 p.m. HappyAndy HalfDork

I know SAABs are pretty picky about sparkplugs and always run best with the OEM NGKs. I would try a set of those first, or if your old plugs were OEM regap them to the exact spec and put them back in as a test. aiso double check your ign wires and cap & rotor. I've seen a worn out center contact cause a very similar problem.
Dec. 26, 2011 3:04 p.m. Travis_K SuperDork

Are NGK plugs OEM in volvos? If thats what you used and it doesnt run right, try a different brand. I have gotten 2 bad sets of NGK plugs before (went from barely running to running fine after replacing the brand new ngk plugs).
Dec. 26, 2011 3:06 p.m. donalson SuperDork

guess i'll order a set of plugs (didn't have the NGK's I'd been using in stock so I grabbed what they had)... the old plugs where ugly thanks to the blown HG...
Dec. 26, 2011 3:11 p.m. Ranger50 Dork

Ditto on different plugs. Same can be said with many Chryslers. Deviating from the stock POS Champions cause all sorts of misses and other problems in most vehicles.
Dec. 26, 2011 3:40 p.m. Curmudgeon SuperDork

Come to think of it, if it has an 'ion sensing' ignition system (it fires a second spark on the exhaust cycle to check combustion efficiency) then the wrong plugs can and will cause all sorts of weirdness. Isuzus with that system that had the wrong plugs would 'clunk' on downshift and the 'Check Trans' light would come on.
Dec. 27, 2011 2:03 p.m. Xceler8x SuperDork

Curmudgeon wrote:

Come to think of it, if it has an 'ion sensing' ignition system (it fires a second spark on the exhaust cycle to check combustion efficiency) then the wrong plugs can and will cause all sorts of weirdness. Isuzus with that system that had the wrong plugs would 'clunk' on downshift and the 'Check Trans' light would come on.

Plugs causing a check trans light?! WTF man. That's nuts.
Dec. 27, 2011 3:37 p.m. Curmudgeon SuperDork

Yup. Really weird. I scratched my head over that one too. It had to do with the spark plugs that were used (Champions IIRC, they were replaced with, again IIRC ND's), the ion sensing module, coils and plugs are all matched. Using anything other than the OE plug would cause it to happen, it could also cause random misfires and rough running.

One of my customers with a 2002? Rodeo wanted to replace his plugs at 30K, I told him sure it can be done but Isuzu says 100K. He wanted to know how much, the OE plugs were ~$13 apiece. He bought Bosch platinums and it ran like ASS until he put the OE plugs back in, thankfully he had saved them.