Help with head gasket

[merkurdriver]

The little single wire grey plug is usually dangling right by the large connector.

[James Wieler]

Hi all,

I keep thinking about this and have some experience in the past with a worn engine and oil additives. If I was there I would flush the engine with Gunk flush or BG flush to get built up sludge out, do an oil change with clean 10w30 conventional oil, add Restore additive for a 4 cylinder engine to the oil and drive it for a tank or two of gas. This will not cure the problem but it will clean the engine of sludge and confirm if the loss of compression is stuck rings or scored cylinder bores. It is a cheap way diagnose the rings/compression if that is the problem. If the cylnders are scored this will improve compression and the engine should run better. It worked for me with an old motor in the past.

cheers

Thanks for sharing that, I can see that happening.
As part of the head gasket I added an oil temp sender to the oil pan. To do this properly I removed the oil pan to drill a hole and weld in a sensor bung. So I also cleaned out the pan, was pretty good actually. It's now hard to check the oil because it's so clean I have a hard time reading the dip stick.
best
James

[James Wieler]

The little single wire grey plug is usually dangling right by the large connector.

That's what I thought, but I can't find it. Can someone send me a pic showing what it looks like and where it's located in the harness? I'm feeling really blind here!
Thanks
James

[Ed Lijewski]

20210225_130941.jpg (133.77 KiB) Viewed 3811 times

YMMV

[andyofcolumbusmerkur]

I have a feeling James is just messing with us at this point.

[James Wieler]

Thanks for the pic. How many wires do you have going into the black triangle shaped connector? I have 4. Looks like you have 3, so maybe my STI is integrated into the triangle connector? It's a white wire with a red stripe, right?
Mine is an '88, what year is your XR?

[Ed Lijewski]

''88.

20210226_144228.jpg (77.96 KiB) Viewed 3802 times

YMMV

[James Wieler]

Thanks for the pic Ed, I think I see the difference. I have 4 wires into the diagnostic connector instead of 3 so my STI is incorporated into that connector. Interesting as both our cars are 1988.
Thanks everyone!
James

[James Wieler]

Ok thanks all, that turned out to the case (the STI wire is part of the diagnostic connector). So I pulled codes and there's nothing remarkable. For KOEOff I got an IRCM module not responding and and VSS not detected (because I have an LA3 in an XR). For KOER I got EGR flow insufficient (I really do have an issue there but I'll worry about that later) and brake on off switch grounded (I think because I didn't hit the brake pedal when I was prompted).
So I purchased a fuel pressure gauge from Amazon (OTC), and I'll let you know how that goes. The car's been sitting for years so I wouldn't be surprised if the gas is all sludgy and clogging the filter/pump. ZRX250cc pointed this out early in this thread, just getting to it now however.
cheers guys
James

[James Wieler]

OK, so fuel pressure is fine (39PSI at idle, 45 psi if I disconnect the vacuum line to the fuel pressure regulator). So I replaced the fuel filter and in the process noticed the gas that spilled all over me was yellowish and tasted like water. Not literally I just mean it wasn't so toxic that it induced vomiting so clearly the gas is stale.
So I dropped the tank and replaced the fuel pump (new strainer too). I'm using a Walbro 255LPH, I did this upgrade years ago so the resistance wire has been removed so this was a simple remove and replace. I cleaned out the gas tank too (which was spotless inside so not much to do there).
Well with fresh fuel it idles much better and doesn't die as I coast to a stop but it still won't rev past 4K RPM under a load. I think it's miss firing (feels like an ignition problem). Maybe I gaped the plugs too big, will check. Spark plug wires cap and rotor are new.
I've pulled codes, I get insufficient EGR flow and a brake on off switch code (I'm using an LA3) so I don't think there's anything wrong with the EEC-IV.
Any fresh ideas
Thanks
James

[andyofcolumbusmerkur]

I think fuel can degrade roughly one octane point a month. I always try to "take her easy" when burning off last years fuel. I don't add any octane boosters or dry gas products but I know some people like to.

[thesameguy]

Samesies....and I add more, good gas as often as possible.

[andyofcolumbusmerkur]

I've also driven someone else's XR where it just would not rev past 4k or so. The cat wasn't clogged. The car ran fine and the owner commuted with it but it wouldn't boost. He said don't rev it past a certain point or it will stall. So I drove it and tried to get it to rev up to redline to figure out what was going on. It was rough like it wasn't firing on all cylinders and wouldn't quite get up to redline. Then when I shifted it stalled out. After coasting to the side of the road it started right back up again and was totally driveable. I assume the wastegate was stuck open or disconnected and that was why it wouldn't boost. But the strange rev limiter type behavior was weird. Makes me wonder about electronics breaking down more and more over time, resistors/capacitors/diodes etc. Like an old piece of audio equipment from 30 or 40 years ago that turns on and plays, but sounds distorted when turned up or in certain modes or settings. Could you swap out the ecm with another LA2/LA3 from a friends car?

[john keefe]

I'm being a dinosaur, but I'm still thinking either bad lifters, or TFI-stator, or the foil wrap around the TFI wires in the harness isn't doing its job anymore, blocking out interference. Also possiblly a weak EEC ground, or bad corrosion on the ground connected to the bottom of the battery tray (which is prone to bad corrosion just above that rain/water slough tray under the battery.

Andy, I had a similar issue with one of my XRs a long time ago. After going through all of the above, it turned out it the yellow EEC power wire in the harness above the battery was badly corroded (some other wires too). About 3x's normal diameter. I believe the issue was that that main power harness is directly above the battery, and with the turbo heat right near there, and standard (not gel-type) batteries, that heat just wicks the battery-fumes right into the harness. Obviously, haven't had that issue since relocating the battery to the trunk, but it would be on my list of things to check.

And even though he had it magnufluxed, shops sometimes do miss the small hairlines if they don't know what the "usual" suspect areas, or weak points are.

[James Wieler]

Thanks John,
The lifters are new, part of the head work and the machine shop is very thorough and knows these heads and where to look. Plus they pressure tested it as well. There's no oil in the coolant or vise versa and the hoses take 10-15 min to pressurize and do so as they get hotter. Temp gauge is rock solid. But these are all great suggestions that I'll look into.

I had significant success this weekend by replacing the fuel pressure regulator. I found fuel in the vacuum hose so clearly the diaphragm had ruptured. Just got back from a test drive and it's MUCH better but there is still a problem but I believe it is now strictly ignition related (so John's comments are particularly timely). It will now rev to red line but only if I use 10% throttle. As soon as I give it more throttle it starts missing. I checked TPS voltage and it's 0.93V at idle. Maybe I should just throw a new one in.

Questions: I'm using #104 Autolite spark plugs. I believe the 754 (or whatever they were) are no longer available. But are the 104's correct? I don't have any old plugs to compare them to for heat range.
Can roller rockers fool the knock sensor? I don't hear any clatter from them, so I'm just spit balling here. Think I'll disconnect the KS as a test.
And lastly, will a miss fire cause a trouble code?
Thanks all
James