Notapilot69 Posted July 14, 2020 Report Share Posted July 14, 2020 Hello all, These threads has been incredibly useful for the two 720s I've owned so far, so thank you everyone. I had an 82 KC 4x4 80k mile survivor i worked on a ton last year before selling. Now I have an 86 KC 4x4 with the Z24i... Bought it for $200 with a blown tranny. Replaced the tranny and all that is good and well, but having other issues. Advancing the throttle slowly allows the engine to rev to redline. If I go wide open anywhere from idle to 5k rpm+, it falls on its face like a slow rev limiter. Tach goes to zero as well until it fires again, then back to zero. Seriously like a really slowly alternating rev limiter. Things I have already checked/replaced: Plugs/cap/rotor/wires - both coils have good spark (at idle at least) and 12v on each positive. Codes: need to redo the process as I see datzenmike posted to double check everything. Without touching any pedals and key on I'm getting 11, 21, 23, 24. I'll redo the test soon and report back. Cleaned MAF Replaced fuel filter Thank you everyone in advance, can't wait to get this thing running right! Devin 1 Quote Link to comment
]2eDeYe Posted July 14, 2020 Report Share Posted July 14, 2020 Welcome. Do you have a list of what the codes mean? 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 8 hours ago, ]2eDeYe said: Welcome. Do you have a list of what the codes mean? Yes, I will get them later tonight when I redo the test the proper way. Ignition switch, throttle position, crank angle sensor, and idle switch I believe are what I got last time. Thanks for the reply Devin 2 Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 The tach going to zero is significant. It means the intake coil is not firing. 2 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 1 minute ago, datzenmike said: The tach going to zero is significant. It means the intake coil is not firing. Thank you for confirming my itial suspicion Mike. I figured it was significant but wanted to do all the simple stuff first. Both coils are both sparking strong at idle, and I'm wondering if there's a compound problem here. I understand both coils fire simultaneously, then the exhaust coil is shut off under heavy load. I disconnected the single wire plug on the distributor hoping it would keep the exhaust coil firing incase something is shutting down the intake coil. It had no effect, which makes me assume BOTH coils are shutting down under heavy load. Any ideas what could cause that? 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Maybe it's the control module inside the dizzy? If I had any parts trucks at picknpull I'd go grab a whole dizzy and swap it out. 1 Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 Ive seen the two wires on the module reversed before. The tach is on the intake coil but if it's reversed, when the exhaust coil is turned off the tach shuts off too... but it would run on the intake coil. The ignition module can't know when the throttle is floored. Can you get it to cut out without driving it??? Can you rev it up in the driveway and get it to stop working? If so check for 12v on each coil + terminal when throttle floored briefly? 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 13 minutes ago, datzenmike said: Yes sir I can, I'll try that tomorrow. Didn't get a chance to re-pull codes yet so I'll do that tomorrow as well. If I grab it by the throttle linkage on the TBI I can rev it up by hand and get to cut out just the same. I also noticed yesterday that my + terminals on both coils are jumped together. I wonder if there was another issue previously and that is a bandaid. Thank you for all the help. I owe you a six pack or two! 1 Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 The intake should be powered directly from the ignition, the exhaust from the first fuse on the left side of the fuse box. I propose that there is a loose wire or a problem with the power being supplied from the ignition. At the same time the fuse is blown so the previous owner simply jumped it to the intake. When power shuts off it shuts off both. First check if the power shuts off when revved. 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Will do. Checked fuses already and they all look alright. There's two empty slots then the first fuse, presumably for ignition. I need to make sure that's proper as well. I found your FSM supplement on 720world the other day as well so I've been looking through there for reference. Good ol Nissan wiring may be at it again. I wonder if them sharing the 12v between the two is causing issues somehow. But I can't imagine how throttle position would cause that to show itself 1 Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 No.... the first position far left <------ end of fuse box is for power to the exhaust coil. If no fuse it needs a 10a fuse. The second position is for powering the automatic choke heater, fuel cut solenoid... 15a 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Worth a relook then. Closest to the drivers seat, I have two blanks then the first fuse. The plot thickens, Mike! 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 So I have replaced the two missing fuses, which is suspicious that they werent there. Just checked voltage and both coils have 12+ volts at idle and all throttle positions, including when it is floored and cuts out. So we aren't losing spark from the coils at least 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Just rechecked codes using the proper method. 11... CAS Crank angle sensor 21...Ignition signal 23... Idle switch 24... Neutral and clutch inhibitor switch I'm shying away from this being a spark issue now that I know the coils aren't losing voltage under load, maybe TPS? Trying to check it with the multimeter but confused about the two separate plugs coming off it. 1 Quote Link to comment
Charlie69 Posted July 15, 2020 Report Share Posted July 15, 2020 You can download thw Nissan 720 Electro injection manual in pdf form. https://forums.nicoclub.com/sharing-this-1986-720-service-manual-electro-injection-supplement-t621604.html 1 Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Thanks charlie. After testing the TPS, I think it may be the issue. When I move the throttle slowly the voltage is linear per the manual. When I move it quickly to another position the voltage drops out completely. Any thoughts? 1 Quote Link to comment
Charlie69 Posted July 15, 2020 Report Share Posted July 15, 2020 Your are welcome. If you do not have that manual and plan on keeping the truck you might down load it soon, I just did so I know it is a good link. I comes up and askes you to sign up but while I was filling out my info the download popped up and asked me where I wanted to save it. I did not finish my info and closed that window after my download was finished. Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Got it downloaded. Thanks a million sir Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 41 minutes ago, Notapilot69 said: Thanks charlie. After testing the TPS, I think it may be the issue. When I move the throttle slowly the voltage is linear per the manual. When I move it quickly to another position the voltage drops out completely. Any thoughts? It needs to know if you are off the gas and coasting or idling, foot off the gas. It also needs to know if full throttle so it can ignore programed fuel map and give maximum performance. Anywhere between if warmed up and above idle there is a fuel map and timing curve for best economy. Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 Makes sense Mike, what concerned me was seeing voltage go to 0 when I moved the throttle rapidly. Really hoping it isn't the TPS since they run $100+. Not sure if this is relevant or not, but looking at the manual I realize I DO NOT have the coils pictures. I have two coils that mirror the non-tbi motors. Guessing someone hacked it together at some point and hoping it isn't related to the issue. Quote Link to comment
datzenmike Posted July 15, 2020 Report Share Posted July 15, 2020 Can or does the TPS come apart? I've seen broken ones and there are two sets of contacts one for idle and one full throttle. Maybe some have a varying resistance? If it comes apart try spraying with electrical contact cleaner. Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 I have it out if the truck now, it moves plenty smoothly, doesn't catch or anything in any spot. It appears the plastic cover may come off but it's all riveted to a metal plate. I'd upload a pic if I knew how Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 I'm going to spray it inside and out with electrical connector cleaner and see if I can get some ohm readings off it Quote Link to comment
Notapilot69 Posted July 15, 2020 Author Report Share Posted July 15, 2020 So on the sensor itself, pins two and three are used per the manual. No continuity until the sensor is rotated to max throttle, then perfect continuity. On the plug that comes off the sensor, Pins 4&5, 120 ohms as long as the throttle is at idle, comes off idle and loses continuity Pins 4&6, 10 kohms across the board Pins 5&6, 10 kohms @ idle down to 200ohms at WOT. Thoughts? Devin Quote Link to comment
datzenmike Posted July 16, 2020 Report Share Posted July 16, 2020 What happens when opened suddenly? I've seen the Z24i in the 720 and I have the 86 D21 Z24i FSM but I know they are not the same engine. Quote Link to comment
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