AHH Disco = NO GO

[DiscoPilot]

Alright after fixing a ton-o-crap i go to drive the disco and ....... runs like crap like barely with throttle input stumbling and sputtering but cleans up around 3k rpms. while nursing the throttle i can just barely drive it like zero power. I have been trying to track down this problem for a week or so, I've replaced some things I know needed replacing. Here is the list of whats been done:

Idle air control valve
MAF
Spark Plugs/wires

Whats weird is that the truck ran perfectly when I parked it. then it didn't

I'm thinking crank or cam angle sensors and O2's but I don't think the O2 's would cause running condtions like this. Now it could easliy be a timing / ignition related issue and creat these conditions so experts Weight in please, I'm running low in the Disco budget and its starting to cut into other projects, not to mention its really pissing me off because i want to go fourwheeling and I'm going insane please help thanks guys!!!!

[6cuda6]

Did it run alright before you changed this stuff??? How long did the truck sit for??? Will the truck idle....if so, start pulling a plug wire at a time (so you pull it off and then put it back on) and listen to how the engine changes...if each one does the same you can rule out internal engine problem..if one or more has no change start by checking the plug (s) and then go further.....

Also check for the odvious...proper firing order, nothing in the air pick up tube for the throtle body, proper distributor rotor etc....

Let me know what happens and i may be able to help you out....later, Dean

[DiscoPilot]

no it ran the same before the stuff and it now runs a little better because the stuff was actually bad. its a 98 so it has coil packs and all the wiring is correct and they all fire since it flattens out and runs right above 3k rpm and runs much better with a stab to WOT. I think I've narrowed it downto a timing issue hence my suspected crank/ cam angle problem but... who knows There really isn't hardly anything else left to check/ change. I have cleaned the entire top end less then 10k miles ago so its all clean. the stumble seems repeatable and the same at various rpms which makes me think its not some bad wire somewhere but some failing sensor. the crank/cam angle and coolant temp and air temp sensors are the only ones left. but i can't believe they would have that kind of effect even if it was stuck in cold start enrichment mode.

[6cuda6]

Something to keep in mind is most of those sensors will throw a code and put the light on if they are bad.... i think your looking at something more simple...like bad fuel etc...

[DiscoPilot]

Originally Posted by 6cuda6

Something to keep in mind is most of those sensors will throw a code and put the light on if they are bad.... i think your looking at something more simple...like bad fuel etc...

yeah I am also wondering why there hasn't been a code thrown but I cleared a bunch of random misfires codes the car hadn't set more than 2 weeks when the problem developed and now its been like 4. I'm not sure how much gas is in it but I'll look into the bad fuel idea, my only quarrel with that idea is that the stumbles seem very repetitious and not random like you would expect with adverse fueling issues be it A/F ratios or bad gas.


Does anyone know of a check procedure for the crank/cam angle sensors?

[6cuda6]

I quess you don´t have another coil pack to try do you...the random miss fires maybe a bad coil or the fuel level is to low (which both happen commonly on VW´s as well). If you have weak spark it will give those symtoms. At this point you may want to run it for a bit at idle and then pull the plugs to see what they look like, my guess is they will be black or very wet...if so you have to find another coil pack to try.....

As far as crank/cam sensors you will get a code and a light because out of tolerence or not working sensors will put the vehicle in base/limp running mode...don´t waste your time with checking them (in my opinion) if the lights not on.

[300bhp/ton]

Personally I think it's more likely something simple. Have you checked the obvious (as the list of items you say you change none would be an obvioius first place to look).

Plugs, leads, distributor, filters. Any of these would be able to cuase such problems.

Also do you think it's fuel or electrical? Often an electrical miss fire will be quite violent where as a fuel related one won't feel as harsh and be more spluttery as opposed to voilent judders. This may help locating the issue.

My TR7 used to have a miss fire in the low rpms under load (high gear low speed), it was quite a violent jolt. All it needed was new plugs/leads and it fixed the problem.


EDIT: My bad, I see you said you changed the plugs/wires , still it's worth double checking an giving the filters a once over.

[DiscoPilot]

I'm thinking eletrical since it runs well with a quick hard stab and runs smooth at zero load over 3k, seems a fueling issue would get worse as the motors demand for fuel increased, I will however check and replace my fuel filter i need to anyway.

[texasrover]

If it were fuel, really fuel you may still have problems over 3k rpms. IAC valve main function is to maintain idle. Should be disengaged and closed once the TP sensor reads you have control of the throttle.

MAF will allow the engine to start and then die after about 600 RPMs if it has failed.

As for the TP sensor failure or fault should limit your revs too. If this has failed you will not be able to throttle up to 3k rpm.

Pump would have trouble meeting the demands of high RPMs. Filter too. Filter problems would be okay at limited demand and should ease with sitting but become problematic with higher demand of fuel such as reving the engine under strain (like driving).

Camshaft sensor will give a MIL
Crankshaft sensor will not allow the engine to start.


Have you checked the battery. I was reading earlier with some post back... that weak batteries could cause hell on these things. Just a thought really!

[texasrover]

Double check all your vac lines... for starters! No cost to look them over.

[wade]

I'm not a mechanic, so take this for what it is worth. It seems reasonable to me that a failing alternator might be lower than necessary output at lower rpms and do better at higher rpms. A drive by autozone and having them check it for free wouldn't hurt.

[DiscoPilot]

Originally Posted by wade

I'm not a mechanic, so take this for what it is worth. It seems reasonable to me that a failing alternator might be lower than necessary output at lower rpms and do better at higher rpms. A drive by autozone and having them check it for free wouldn't hurt.

1000 mile old Mean Green alternator that will run all the lights and everything while misfiring electrical load has no bearing good thought though.

[6cuda6]

DiscoPilot....that truck of yours have a MAF sensor on it???? If it does....your describing a problem i had with a VW that was chipped that i was working on...same type of throtle responce but the VW had no engine light or codes.....worth a shot if you have one to swap......

[DiscoPilot]

Originally Posted by 6cuda6

DiscoPilot....that truck of yours have a MAF sensor on it???? If it does....your describing a problem i had with a VW that was chipped that i was working on...same type of throtle responce but the VW had no engine light or codes.....worth a shot if you have one to swap......

MAF and IACV were the first 2 things I swapped

[bruinlad]

My old 7 series bimmer behaved exactly like that on a bad 02 sensor. Where the heck is Beezel??? You can chime in anytime.