94 Grand Cherokee Missing/stumbling at 80kmh - bad gas, please help!

[Sinoed]

I have a 94 grand cherokee with about 200K on it. Since the mileage was getting up there I decided to do a tune-up on it. I replaced the cap, rotor, wires, plugs, pcv valve, air filter & changed the oil. I also replaced the rad and lower hose at the same time since it was gone. I drove it around for about a week - and the truck was running fantastic - so I was very happy. Unfortunately it didn't last that long. I was heading up to a concert on Friday night and picked up a tank of some really foul gas. The truck ran well for about a minute after I left the station - long enough for the gas to make it through the lines before it was barely driveable. I limped to the next exit, filled the rest of the tank with Premium and added some methyl hydrate to try and displace the water. Its an automatic but I two footed it home, since it was stalling at idle through town. I managed to get it home where I added a new bottle of injector cleaner. I tried driving it around to run out the bad gas, this is now the second tank of premium I've added and its still running rough.

I discovered that the water burning through the lines superheated the muffler and cat & I had them replaced. I've also changed the fuel filter and cleaned out the egr valve. I replaced the plugs (again). Each thing seems to have improved the truck but I'm getting a really bad miss under highway speed (around 80-90 km). It doesn't seem to be bad driving in town (around 30-40). It seems to be running lean on cyl 2 & 4? I don't know whether to suspect something like a couple of injectors or an ECM..? Any help is GREATLY appreciated - I'm running out of ideas.

[JDPascal]

Is your check engine lite on??

Have you checked for codes???

You didn't mention what engine you have or I missed that info????

Let us know what you got for these questions.


JD

[Sinoed]

Whoops! Ok - let me clarify. It has the 5.2L engine, the check engine light is not on. I checked for codes by cycling the key and the only one that came up was battery disconnected (from when I replaced the rad) - so I don't have any codes set.

[JDPascal]

Are you basing your suspected lean condition at #2 and #4 on a plug read??

It would seem with all you have replaced that the only things left are the injectors and the PCM.... and with the onset of the problem beginning with the bad gas, it may be that the gas/water and methylhydrate combo seized an injector or two....

The best read on plugs is after a high speed run at full temp with as little idle and low speed operation as possible.

If another plug read still shows lean on those cylinders, it might be worth it to try a couple of injectors in those cylinders.. $80usd a piece would be the approx. cost for new ones.....

Questions:

Does it miss at equivelent rpm for 80 kph?

Is the miss different under load than no load?

Is the miss detectable at engine idle?

JD

[Sinoed]

I've tried two sets of plugs now with similar results. I'm not sure exactly what is going on with it, but it seems like its possibly worse today. It does miss at engine idle and almost feels like its going to stall, although it doesn't seem *different* under load than no load (as in type) but much harsher at highway speeds. When idling at about 700rpm it does miss. I'm suspicious of an injector/fuel rail now because its started rattling on the left hand side. I think I might take it in to a friend of mine who is excellent with tracking this kind of stuff down..

[Sinoed]

So anyways, the wonderful folks at the last garage who wanted to charge a bunch of fees for wasting my time left the cap unscrewed (problem #1). The wires were arcing so the new ones are bad (problem #2). The coil was breaking down under load and causing a misfire (problem #3). So fixed all of that, and now its started stalling - there is more yet to be found..

[dksob81]

Originally Posted by Sinoed

So anyways, the wonderful folks at the last garage who wanted to charge a bunch of fees for wasting my time left the cap unscrewed (problem #1). The wires were arcing so the new ones are bad (problem #2). The coil was breaking down under load and causing a misfire (problem #3). So fixed all of that, and now its started stalling - there is more yet to be found..

I suspect the loose Distr. Cap caused both the wires and Ignition Coil to go bad. I had this same problem on my 94 5.2, I had a bad wire which arced real bad and while playing around in the snow and it overheated my Ignition coil, replaced it with another one from Autozone (WELLS BRAND) last about 30 minutes died again, went to another local part store and got another put it in fire up then died about 2 mintes later, well got it home did some troubleshooting (with engine running) played with the wires (making sure non of them were loose from the plugs or distr. cap) and got jolted, one of my plug wires got stuck on my exhaust manifold a few weeks earlier and melted it little bit causing it to arc (especially under heavy load/higher RPM's) and eventually overheating my Ignition Coil.

Story about the manifold.... I replaced my exhaust manifold gasket a few weeks before and right after that ran up the street to the store and when I came out restarted it and it had a rough idle. Took it home and seen the problem with the plug wire on the manifold, removed it put the heat sheild back on and forgot to replace the wire, well it bit me in the a$$ a few weeks later when this problem occur.

STALLING....
Does your check engine light come on?
Does it stall under throttle pressure?

[Sinoed]

Ok, finally solved this disaster on wheels! Something didn't seem right, so I pulled the cap & rotor off again to double check since my tune-up buddy just fastened it back down. Frankly I'm suprised it ran - the new cap & rotor failed hard. The cap wasn't too bad aside from the burn marks & scratch on the inside - but the metal tab on the rotor broke off. The spark was jumping from the center post to the points and essentially liquified the plastic rotor. I'd never seen a rotor melt down until now.. needless to say I'm not going back to the shop that tried to charge the diagnosing fees because they unscrewed the cap! I can think of a few choice words for that piece of work because I wouldn't have made it home tonight for sure. Thank you very much for helping me out!