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1990 740 B234 Revival!

3wagons

3wagons

Active member
Joined
Jul 3, 2019
Location
NW GA
Scored this jewel today. 2 owner car with 88k miles. Was parked when it started running rough. Previous owner said it will run if you give it gas. Look likes it will clean up good. Seats are almost perfect.

Checked the timing belt and it looked great. It's been done at some point, but no clue when so it will be on the list. Added some gas and a hot battery and it does try to run. Main pump is priming for about 20 seconds with the key on for some reason, and I don't think the intank pump is working. The HP pump also stays on even if you cycle the key off. Swapped fuel pump relays and it behaves the same. Intake gasket is definitely shot as it's blown out in a couple places. Will check it out more Friday.

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Had some time today to start digging into this one. Evicted some ants that had taken up residence in the trunk and got some of the loose stuff off it with the shop vac.

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I couldn't get the fuel line loose from the fuel rail without risking damaging the rail, so I disconnected the line at the firewall and used a section of 240 fuel line to make an adapter. Fuel pressure was 46 psi and retained over 20 psi after an hour.
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Next up was investigating the hard misfires while trying to run. The valve cover gasket was leaking in several places, including into the plug wells. Over 2 inches of oil in 1 and 2, and almost an inch in 3.
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I have a new gasket as well as plugs and wires coming tomorrow hopefully.
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Also tested the ECT sensor today. 2800 ohms at about 70 degrees. Nice that on the B234 the sensor is behind the thermostat.
 
Thanks to all for the encouragement!

Finally had time to work on this one a little. First valve cover gasket was a bust from roackauto. Wasn't a kit as described and was brittle.
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Quick and easy refund on it and ordered an elring kit. Worked great. Unfortunately, no change in the rough running and no idle. Did a quick compression test and all cylinders were 190-200 psi.

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Just ordered an intake gasket from IPD. Hopefully it gets here this week.
 
Did a little digging today. Found a jumper wire the fuel pump relay. Confirms at least one issue with the ECU.
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It is nice being able to pull the fuse box out on these 7/9 series.


Also, considering I've been in and out of this car several times over the last couple weeks, I was surprised to have overlooked this.
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Well, may not have been my best call, but it did work out ok.

Settled on the Ecu being bad and not having a spare 16v ecu laying around, decided to toss in a 8 valve 2.4 Ecu and see if the fuel pump prime would work properly after removing the ground wire splice. It worked as intended, priming for 2 seconds or so. Then of course I had to try and crank it. It started fine and held an idle. Very obvious the fueling was off but it did confirm the ECU issue. Guess I'll be tracking down a -571 or -928 ECU now.
 
3wagons said:
Well, may not have been my best call, but it did work out ok.

Settled on the Ecu being bad and not having a spare 16v ecu laying around, decided to toss in a 8 valve 2.4 Ecu and see if the fuel pump prime would work properly after removing the ground wire splice. It worked as intended, priming for 2 seconds or so. Then of course I had to try and crank it. It started fine and held an idle. Very obvious the fueling was off but it did confirm the ECU issue. Guess I'll be tracking down a -571 or -928 ECU now.
Click to expand...
Hey, I might have a 16 valve ecu! I'll check tomorrow
 
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