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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2007Cressida w/newly rebuilt engine suddenly developed a miss
I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was running like a clock this morning. I fired it up tonight and it displayed a severe miss. I'm getting spark from all distributor contacts to the wires, confirmed by pulling them out one at a time while the engine was running. Results of a compression test after it sat for about an hour 1 180 2 175 3 160 4 189 5 160 6 195 I put it back together and fired it up to get it up to operating temp again and did it again immediately. During this warm up, I noticed the miss was still there but less pronounced than it had been previously. 1 200 2 180 3 170 4 180 5 170 6 195 All the cylinders came up somewhat, some more than others. The shop manual lists 120 psi as the low minimum, obviously they're all over that. I squired some oil in the two low cylinders 3 & 5, 3 came up to 180, 5 came up to 200. Just for grins I put oil in the #1 cylinder, which was the high of the second test, it went to 210. I'm a bit concerned about what appears to be a fairly wide gap between the lowest and highest cylinders. Is this normal for 1200 miles out from a rebuild? Also, wondering about how some of the cyls increased up more than others when checked hot. The miss I was experiencing was as if one of the cylinders had flat quit - running rough and an obvious *pap pap pap* at the exhaust pipe where it's normally a quite, silky whoosh. Do any of these cyl pressure differences seem to be enough to cause this? It's a new engine, hasn't overheated, the lowest cyls aren't adjacent and it isn't losing any water so it would seem a head gasket isn't indicated. It certainly didn't blow a gasket sitting there in the parking lot. Not burning any oil as far as I can tell. I did the first oil change at around 1000 miles and it's still quite clear on the dipstick after 200 - 300 miles since changing. The plugs aren't new but they look okay, none of the electrodes are fried. Ran like a Swiss watch this morning and ever since the rebuild. Fired it up, and now it's got a problem. <scratch head> It seems like something that could go bad quick. Maybe an injector? Any definitive way to check with them installed? Other theories? Thanks for all input. i think those are good compression numbers. all are over 150. there is only about 15% difference between the lowest and highest. Except that the spread is almost 20%. The highest is 195, the lowest is 160. This difference is 35. 19 is 10% of the highest reading, and 38 would be 20% of the highest. The spread from highest to lowest is closer to 20% than 15%. >i think those are good compression numbers. all are over 150. there is > only about 15% difference between the lowest and highest. >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was > running like a clock this morning. I fired it up tonight and it > displayed a severe miss. Does it have hydraulic or adjustable tappets? Could well be a tight valve that's bedding in and closed up the gap, causing the valve to leak. This would explain the change when the engine temp varies. Check all the usual other suspects like injectors, injector seals on the intake and air leaks somewhere. SD > >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was > > running like a clock this morning. I fired it up tonight and it [quoted text clipped - 3 lines] > that's bedding in and closed up the gap, causing the valve to leak. This > would explain the change when the engine temp varies. After putting everything back together again, the problem has disappeared. Running silky smooth again...hmmm Wondering if maybe a spark plug boot that wasn't quite snapped on tight lifted off. The point at which the boots snap into the cover and the contacts snap onto the plugs is pretty much the same, maybe causing some upward tension. Re: the lifters, it's a DOHC, I was under the impression they're hydraulic however I know they're adjustable by way of shims and the shop manual has procedures to check and replace them. It's had a couple of head rebuilds since the car was new but I don't know for a fact whether this was checked. I think it might be worth doing anyway since the car has over 130k on it. Thanks for the suggestions. > On Dec 10, 7:13 am, "Stewart DIBBS" > <s...@pixcl.com> wrote: [quoted text clipped - 24 lines] > pretty much the same, maybe > causing some upward tension. In the past I have found my #1 wire like that after working on the engine. And then forgetting to reconnect the plug wire when done. But the engine ran fine so I doubt it. A word of warning though. If that center cover (head cover #3) the wires go thru is not water tight do not let water gets in there. The #2 and #3 plug valleys will never dry out (even if it boils) and their burried under the intake. > Re: the lifters, it's a DOHC, I was > under the impression they're [quoted text clipped - 7 lines] > it might be worth doing anyway > since the car has over 130k on it. Could have sworn someone said "I rebuilt the 7MGE in this Cressida about 1200 miles ago"!!!!!!! 8) > Thanks for the suggestions. >> and replace them. It's had a >> couple of head rebuilds since the car was new but I don't know for a [quoted text clipped - 4 lines] > 1200 > miles ago"!!!!!!! 8) 130K and a *COUPLE* of head rebuilds?!?! Whew! My Supra has 200+ and hasn't had a head rebuild yet! You must *REALLY* like this car! > > It's had a > > couple of head rebuilds since the car [quoted text clipped - 6 lines] > the 7MGE in this Cressida about 1200 > miles ago"!!!!!!! 8) I should clarify the history. The car has 133K on it. The heads were rebuilt once at around 70K when the car overheated on my dad To be more exact, he was told the engine had been rebuilt top to bottom. After I took possession of the car, I talked to the owner of the shop who told me it had been rebuilt, top to bottom, rings, pistons, bearings, turned the crank, the works. When it developed some issues the machine shop I took it to determined that there had been a fairly recent valve job but the bottom of the engine was untouched. It had factory pistons and bearings. The bore reflected what he would expect to find with the original engine. He said there was no way it only had 20 - 30k miles on it. I.e. the shop owner who was supposedly a "friend" of my parents lied and charged them for a complete rebuild. He lied to them and he lied to me. So, I had the engine gone over top to bottom by this shop, which was head job #2. When this most recent malady occurred about 25K - 30K later, the engine rebuilder I took it to felt that with that few miles since a rebuild, it would be a waste of money to do another complete head job, they advised that it looked fine, tested out fine. They resurfaced the head and did the machine work on the engine - bored the pistons, decked the block. The con rods checked out okay. They polished the crank but said there was no need to turn it. So, that's where the two head jobs occurred. >> >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was >> > running like a clock this morning. I fired it up tonight and it [quoted text clipped - 6 lines] >After putting everything back together again, the problem has >disappeared. Running silky smooth again...hmmm >Wondering if maybe a spark plug boot that wasn't quite snapped on >tight lifted off. The point at which the boots snap into the cover and >the contacts snap onto the plugs is pretty much the same, maybe >causing some upward tension. If you're not feeling a slight click when you push in the plug wire, replace your wires. >Re: the lifters, it's a DOHC, I was under the impression they're >hydraulic however I know they're adjustable by way of shims and the >shop manual has procedures to check and replace them. It's had a >couple of head rebuilds since the car was new but I don't know for a >fact whether this was checked. I think it might be worth doing anyway >since the car has over 130k on it. COUPLE? If that's true, you'd be better off just replacing the 7MGE. Surely you know a used one with under 40K can be had for less than you can buy one at a local junkyard? Google. Be amazed.  Signaturegburnore at DataBasix dot Com --------------------------------------------------------------------------- How you look depends on where you go. --------------------------------------------------------------------------- Gary L. Burnore | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ Official .sig, Accept no substitutes. | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ | ÝÛ 0 1 7 2 3 / Ý³Þ 3 7 4 9 3 0 Û³ Black Helicopter Repair Services, Ltd.| Official Proof of Purchase =========================================================================== >I rebuilt the 7MGE in this Cressida >about 1200 miles ago, it was [quoted text clipped - 92 lines] > > Thanks for all input. I don't think your compression is a problem. Or your gauge is very accurate. If you need the numbers my TSRM shows the warm engine pressure @ 156 psi. The minimum is 128 and the difference between each cylinder less than 14 psi. When you put it back together and the problem changed that is a big clue. I would assume you checked the OBD diagnostic output is "normal" right! Check the engine air intake pipes and vacuum hoses for leaks. The one from the intake pipe to the power steering is real easy to miss for example. Check the spark plug wires with a ohm meter. Measure from the terminal inside the distributor cap to the end of each wire. Maximum resistance is 25 ohms. I would check the coil wire and for intake leaks before the throttle body first. GL Dan >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was > running like a clock this morning. I fired it up tonight and it [quoted text clipped - 60 lines] > > Thanks for all input. Me thinks your motor is not well. You are way above the min. spec, but you have a very wide difference between the high and low pistons, and they are adjacent to one another. I seem to recall the spread should not exceed 10% -- your high pressure is 200, the weakest one should be at least 180. Your weakest cylinder is nearly 20% below the strongest one. That can't be good. >>I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was >> running like a clock this morning. I fired it up tonight and it [quoted text clipped - 68 lines] >weakest one should be at least 180. Your weakest cylinder is nearly 20% >below the strongest one. That can't be good. From the 7MGE Manual: The engine must be warm when performing the test. The test must be performed as quickly as possible. Meaning waiting between testing of each cyl can slew the results. Std Pressure: 156PSI or more. Min Pressure: 128PSI The important part: Difference between cyl: 14PSI So using his second test: 1 - 2 Diff 20 Bad 2 - 3 Diff 10 Ok 3 - 4 Diff 10 Ok 4 - 5 Diff 10 Ok 5 - 6 Diff 15 Barely Bad. Since adding oil to each cyl caused the test to go up fairly uniformly, it's likely that the rings are shot. Signaturegburnore at DataBasix dot Com --------------------------------------------------------------------------- How you look depends on where you go. --------------------------------------------------------------------------- Gary L. Burnore | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ Official .sig, Accept no substitutes. | ÝÛ³ºÝ³Þ³ºÝ³³Ýۺݳ޳ºÝ³Ý³Þ³ºÝ³ÝÝÛ³ | ÝÛ 0 1 7 2 3 / Ý³Þ 3 7 4 9 3 0 Û³ Black Helicopter Repair Services, Ltd.| Official Proof of Purchase =========================================================================== >>>I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was <snip> > Since adding oil to each cyl caused the test to go up fairly > uniformly, it's likely that the rings are shot. Uh, look at the last sentence above the "snip." If anything, the rings aren't SEATED yet! >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was > running like a clock this morning. I fired it up tonight and it [quoted text clipped - 60 lines] > > Thanks for all input. Most likely, one of the spark plug wires was not installed correctly. To find the miss, pull the spark plug wires one at a time until there is no change when the spark plug wire is pulled. The compression test should be performed when the engine is hot, My guess for the variance in compression figures is that the head bolts were not torqued quite right, but good enough. IOW, they could have been torqued more evenly, but they are not uneven enough to mess with. SignatureRay O (correct punctuation to reply) >I rebuilt the 7MGE in this Cressida about 1200 miles ago, it was >running like a clock this morning. I fired it up tonight and it [quoted text clipped - 60 lines] > >Thanks for all input. That compression is fine. Many things will effect readingss a little. Unburn fuel washes oil from the rings and lowers compression. Adding oil down the spark plug hole increases the effect compression ratio by occupying space. Thus even with no compression leakage whatsoever you could easily add enough oil to peg your gauge if you wanted. Don www.donsautomotive.com |
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